jdk8-mips64-public/langtools: src/share/classes/com/sun/tools/javac/comp/DeferredAttr.java@ca5783d9a597 (annotated)

src/share/classes/com/sun/tools/javac/comp/DeferredAttr.java@ca5783d9a597 (annotated)

src/share/classes/com/sun/tools/javac/comp/DeferredAttr.java

Mon, 16 Oct 2017 16:07:48 +0800

author: aoqi
date: Mon, 16 Oct 2017 16:07:48 +0800
changeset 2893: ca5783d9a597
parent 2811: 610ec7dcf431
parent 2702: 9ca8d8713094
permissions: -rw-r--r--

merge

 /*
  * Copyright (c) 2012, 2015, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 only, as
  * published by the Free Software Foundation.  Oracle designates this
  * particular file as subject to the "Classpath" exception as provided
  * by Oracle in the LICENSE file that accompanied this code.
  *
  * This code is distributed in the hope that it will be useful, but WITHOUT
  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  * version 2 for more details (a copy is included in the LICENSE file that
  * accompanied this code).
  *
  * You should have received a copy of the GNU General Public License version
  * 2 along with this work; if not, write to the Free Software Foundation,
  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  *
  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  * or visit www.oracle.com if you need additional information or have any
  * questions.
  */
 package com.sun.tools.javac.comp;
 import com.sun.source.tree.LambdaExpressionTree.BodyKind;
 import com.sun.tools.javac.code.*;
 import com.sun.tools.javac.tree.*;
 import com.sun.tools.javac.util.*;
 import com.sun.tools.javac.util.JCDiagnostic.DiagnosticPosition;
 import com.sun.tools.javac.code.Symbol.*;
 import com.sun.tools.javac.code.Type.*;
 import com.sun.tools.javac.comp.Attr.ResultInfo;
 import com.sun.tools.javac.comp.Infer.InferenceContext;
 import com.sun.tools.javac.comp.Resolve.MethodResolutionPhase;
 import com.sun.tools.javac.tree.JCTree.*;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.EnumSet;
 import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
 import java.util.Map;
 import java.util.Set;
 import java.util.WeakHashMap;
 import static com.sun.tools.javac.code.Kinds.VAL;
 import static com.sun.tools.javac.code.TypeTag.*;
 import static com.sun.tools.javac.tree.JCTree.Tag.*;
 /**
  * This is an helper class that is used to perform deferred type-analysis.
  * Each time a poly expression occurs in argument position, javac attributes it
  * with a temporary 'deferred type' that is checked (possibly multiple times)
  * against an expected formal type.
  *
  *  <p><b>This is NOT part of any supported API.
  *  If you write code that depends on this, you do so at your own risk.
  *  This code and its internal interfaces are subject to change or
  *  deletion without notice.</b>
  */
 public class DeferredAttr extends JCTree.Visitor {
     protected static final Context.Key<DeferredAttr> deferredAttrKey =
         new Context.Key<DeferredAttr>();
     final Attr attr;
     final Check chk;
     final JCDiagnostic.Factory diags;
     final Enter enter;
     final Infer infer;
     final Resolve rs;
     final Log log;
     final Symtab syms;
     final TreeMaker make;
     final Types types;
     final Flow flow;
     final Names names;
     final TypeEnvs typeEnvs;
     public static DeferredAttr instance(Context context) {
         DeferredAttr instance = context.get(deferredAttrKey);
         if (instance == null)
             instance = new DeferredAttr(context);
         return instance;
     }
     protected DeferredAttr(Context context) {
         context.put(deferredAttrKey, this);
         attr = Attr.instance(context);
         chk = Check.instance(context);
         diags = JCDiagnostic.Factory.instance(context);
         enter = Enter.instance(context);
         infer = Infer.instance(context);
         rs = Resolve.instance(context);
         log = Log.instance(context);
         syms = Symtab.instance(context);
         make = TreeMaker.instance(context);
         types = Types.instance(context);
         flow = Flow.instance(context);
         names = Names.instance(context);
         stuckTree = make.Ident(names.empty).setType(Type.stuckType);
         typeEnvs = TypeEnvs.instance(context);
         emptyDeferredAttrContext =
             new DeferredAttrContext(AttrMode.CHECK, null, MethodResolutionPhase.BOX, infer.emptyContext, null, null) {
                 @Override
                 void addDeferredAttrNode(DeferredType dt, ResultInfo ri, DeferredStuckPolicy deferredStuckPolicy) {
                     Assert.error("Empty deferred context!");
                 }
                 @Override
                 void complete() {
                     Assert.error("Empty deferred context!");
                 }
                 @Override
                 public String toString() {
                     return "Empty deferred context!";
                 }
             };
     }
     /** shared tree for stuck expressions */
     final JCTree stuckTree;
     /**
      * This type represents a deferred type. A deferred type starts off with
      * no information on the underlying expression type. Such info needs to be
      * discovered through type-checking the deferred type against a target-type.
      * Every deferred type keeps a pointer to the AST node from which it originated.
      */
     public class DeferredType extends Type {
         public JCExpression tree;
         Env<AttrContext> env;
         AttrMode mode;
         SpeculativeCache speculativeCache;
         DeferredType(JCExpression tree, Env<AttrContext> env) {
             super(null);
             this.tree = tree;
             this.env = attr.copyEnv(env);
             this.speculativeCache = new SpeculativeCache();
         }
         @Override
         public TypeTag getTag() {
             return DEFERRED;
         }
         @Override
         public String toString() {
             return "DeferredType";
         }
         /**
          * A speculative cache is used to keep track of all overload resolution rounds
          * that triggered speculative attribution on a given deferred type. Each entry
          * stores a pointer to the speculative tree and the resolution phase in which the entry
          * has been added.
          */
         class SpeculativeCache {
             private Map<Symbol, List<Entry>> cache =
                     new WeakHashMap<Symbol, List<Entry>>();
             class Entry {
                 JCTree speculativeTree;
                 ResultInfo resultInfo;
                 public Entry(JCTree speculativeTree, ResultInfo resultInfo) {
                     this.speculativeTree = speculativeTree;
                     this.resultInfo = resultInfo;
                 }
                 boolean matches(MethodResolutionPhase phase) {
                     return resultInfo.checkContext.deferredAttrContext().phase == phase;
                 }
             }
             /**
              * Retrieve a speculative cache entry corresponding to given symbol
              * and resolution phase
              */
             Entry get(Symbol msym, MethodResolutionPhase phase) {
                 List<Entry> entries = cache.get(msym);
                 if (entries == null) return null;
                 for (Entry e : entries) {
                     if (e.matches(phase)) return e;
                 }
                 return null;
             }
             /**
              * Stores a speculative cache entry corresponding to given symbol
              * and resolution phase
              */
             void put(JCTree speculativeTree, ResultInfo resultInfo) {
                 Symbol msym = resultInfo.checkContext.deferredAttrContext().msym;
                 List<Entry> entries = cache.get(msym);
                 if (entries == null) {
                     entries = List.nil();
                 }
                 cache.put(msym, entries.prepend(new Entry(speculativeTree, resultInfo)));
             }
         }
         /**
          * Get the type that has been computed during a speculative attribution round
          */
         Type speculativeType(Symbol msym, MethodResolutionPhase phase) {
             SpeculativeCache.Entry e = speculativeCache.get(msym, phase);
             return e != null ? e.speculativeTree.type : Type.noType;
         }
         /**
          * Check a deferred type against a potential target-type. Depending on
          * the current attribution mode, a normal vs. speculative attribution
          * round is performed on the underlying AST node. There can be only one
          * speculative round for a given target method symbol; moreover, a normal
          * attribution round must follow one or more speculative rounds.
          */
         Type check(ResultInfo resultInfo) {
             DeferredStuckPolicy deferredStuckPolicy;
             if (resultInfo.pt.hasTag(NONE) || resultInfo.pt.isErroneous()) {
                 deferredStuckPolicy = dummyStuckPolicy;
             } else if (resultInfo.checkContext.deferredAttrContext().mode == AttrMode.SPECULATIVE ||
                     resultInfo.checkContext.deferredAttrContext().insideOverloadPhase()) {
                 deferredStuckPolicy = new OverloadStuckPolicy(resultInfo, this);
             } else {
                 deferredStuckPolicy = new CheckStuckPolicy(resultInfo, this);
             }
             return check(resultInfo, deferredStuckPolicy, basicCompleter);
         }
         private Type check(ResultInfo resultInfo, DeferredStuckPolicy deferredStuckPolicy,
                 DeferredTypeCompleter deferredTypeCompleter) {
             DeferredAttrContext deferredAttrContext =
                     resultInfo.checkContext.deferredAttrContext();
             Assert.check(deferredAttrContext != emptyDeferredAttrContext);
             if (deferredStuckPolicy.isStuck()) {
                 deferredAttrContext.addDeferredAttrNode(this, resultInfo, deferredStuckPolicy);
                 return Type.noType;
             } else {
                 try {
                     return deferredTypeCompleter.complete(this, resultInfo, deferredAttrContext);
                 } finally {
                     mode = deferredAttrContext.mode;
                 }
             }
         }
     }
     /**
      * A completer for deferred types. Defines an entry point for type-checking
      * a deferred type.
      */
     interface DeferredTypeCompleter {
         /**
          * Entry point for type-checking a deferred type. Depending on the
          * circumstances, type-checking could amount to full attribution
          * or partial structural check (aka potential applicability).
          */
         Type complete(DeferredType dt, ResultInfo resultInfo, DeferredAttrContext deferredAttrContext);
     }
     /**
      * A basic completer for deferred types. This completer type-checks a deferred type
      * using attribution; depending on the attribution mode, this could be either standard
      * or speculative attribution.
      */
     DeferredTypeCompleter basicCompleter = new DeferredTypeCompleter() {
         public Type complete(DeferredType dt, ResultInfo resultInfo, DeferredAttrContext deferredAttrContext) {
             switch (deferredAttrContext.mode) {
                 case SPECULATIVE:
                     //Note: if a symbol is imported twice we might do two identical
                     //speculative rounds...
                     Assert.check(dt.mode == null || dt.mode == AttrMode.SPECULATIVE);
                     JCTree speculativeTree = attribSpeculative(dt.tree, dt.env, resultInfo);
                     dt.speculativeCache.put(speculativeTree, resultInfo);
                     return speculativeTree.type;
                 case CHECK:
                     Assert.check(dt.mode != null);
                     return attr.attribTree(dt.tree, dt.env, resultInfo);
             }
             Assert.error();
             return null;
         }
     };
     DeferredTypeCompleter dummyCompleter = new DeferredTypeCompleter() {
         public Type complete(DeferredType dt, ResultInfo resultInfo, DeferredAttrContext deferredAttrContext) {
             Assert.check(deferredAttrContext.mode == AttrMode.CHECK);
             return dt.tree.type = Type.stuckType;
         }
     };
     /**
      * Policy for detecting stuck expressions. Different criteria might cause
      * an expression to be judged as stuck, depending on whether the check
      * is performed during overload resolution or after most specific.
      */
     interface DeferredStuckPolicy {
         /**
          * Has the policy detected that a given expression should be considered stuck?
          */
         boolean isStuck();
         /**
          * Get the set of inference variables a given expression depends upon.
          */
         Set<Type> stuckVars();
         /**
          * Get the set of inference variables which might get new constraints
          * if a given expression is being type-checked.
          */
         Set<Type> depVars();
     }
     /**
      * Basic stuck policy; an expression is never considered to be stuck.
      */
     DeferredStuckPolicy dummyStuckPolicy = new DeferredStuckPolicy() {
         @Override
         public boolean isStuck() {
             return false;
         }
         @Override
         public Set<Type> stuckVars() {
             return Collections.emptySet();
         }
         @Override
         public Set<Type> depVars() {
             return Collections.emptySet();
         }
     };
     /**
      * The 'mode' in which the deferred type is to be type-checked
      */
     public enum AttrMode {
         /**
          * A speculative type-checking round is used during overload resolution
          * mainly to generate constraints on inference variables. Side-effects
          * arising from type-checking the expression associated with the deferred
          * type are reversed after the speculative round finishes. This means the
          * expression tree will be left in a blank state.
          */
         SPECULATIVE,
         /**
          * This is the plain type-checking mode. Produces side-effects on the underlying AST node
          */
         CHECK;
     }
     /**
      * Routine that performs speculative type-checking; the input AST node is
      * cloned (to avoid side-effects cause by Attr) and compiler state is
      * restored after type-checking. All diagnostics (but critical ones) are
      * disabled during speculative type-checking.
      */
     JCTree attribSpeculative(JCTree tree, Env<AttrContext> env, ResultInfo resultInfo) {
         final JCTree newTree = new TreeCopier<Object>(make).copy(tree);
         Env<AttrContext> speculativeEnv = env.dup(newTree, env.info.dup(env.info.scope.dupUnshared()));
         speculativeEnv.info.scope.owner = env.info.scope.owner;
         Log.DeferredDiagnosticHandler deferredDiagnosticHandler =
                 new Log.DeferredDiagnosticHandler(log, new Filter<JCDiagnostic>() {
             public boolean accepts(final JCDiagnostic d) {
                 class PosScanner extends TreeScanner {
                     boolean found = false;
                     @Override
                     public void scan(JCTree tree) {
                         if (tree != null &&
                                 tree.pos() == d.getDiagnosticPosition()) {
                             found = true;
                         }
                         super.scan(tree);
                     }
                 };
                 PosScanner posScanner = new PosScanner();
                 posScanner.scan(newTree);
                 return posScanner.found;
             }
         });
         try {
             attr.attribTree(newTree, speculativeEnv, resultInfo);
             unenterScanner.scan(newTree);
             return newTree;
         } finally {
             unenterScanner.scan(newTree);
             log.popDiagnosticHandler(deferredDiagnosticHandler);
         }
     }
     //where
         protected UnenterScanner unenterScanner = new UnenterScanner();
         class UnenterScanner extends TreeScanner {
             @Override
             public void visitClassDef(JCClassDecl tree) {
                 ClassSymbol csym = tree.sym;
                 //if something went wrong during method applicability check
                 //it is possible that nested expressions inside argument expression
                 //are left unchecked - in such cases there's nothing to clean up.
                 if (csym == null) return;
                 typeEnvs.remove(csym);
                 chk.compiled.remove(csym.flatname);
                 syms.classes.remove(csym.flatname);
                 super.visitClassDef(tree);
             }
         }
     /**
      * A deferred context is created on each method check. A deferred context is
      * used to keep track of information associated with the method check, such as
      * the symbol of the method being checked, the overload resolution phase,
      * the kind of attribution mode to be applied to deferred types and so forth.
      * As deferred types are processed (by the method check routine) stuck AST nodes
      * are added (as new deferred attribution nodes) to this context. The complete()
      * routine makes sure that all pending nodes are properly processed, by
      * progressively instantiating all inference variables on which one or more
      * deferred attribution node is stuck.
      */
     class DeferredAttrContext {
         /** attribution mode */
         final AttrMode mode;
         /** symbol of the method being checked */
         final Symbol msym;
         /** method resolution step */
         final Resolve.MethodResolutionPhase phase;
         /** inference context */
         final InferenceContext inferenceContext;
         /** parent deferred context */
         final DeferredAttrContext parent;
         /** Warner object to report warnings */
         final Warner warn;
         /** list of deferred attribution nodes to be processed */
         ArrayList<DeferredAttrNode> deferredAttrNodes = new ArrayList<DeferredAttrNode>();
         DeferredAttrContext(AttrMode mode, Symbol msym, MethodResolutionPhase phase,
                 InferenceContext inferenceContext, DeferredAttrContext parent, Warner warn) {
             this.mode = mode;
             this.msym = msym;
             this.phase = phase;
             this.parent = parent;
             this.warn = warn;
             this.inferenceContext = inferenceContext;
         }
         /**
          * Adds a node to the list of deferred attribution nodes - used by Resolve.rawCheckArgumentsApplicable
          * Nodes added this way act as 'roots' for the out-of-order method checking process.
          */
         void addDeferredAttrNode(final DeferredType dt, ResultInfo resultInfo,
                 DeferredStuckPolicy deferredStuckPolicy) {
             deferredAttrNodes.add(new DeferredAttrNode(dt, resultInfo, deferredStuckPolicy));
         }
         /**
          * Incrementally process all nodes, by skipping 'stuck' nodes and attributing
          * 'unstuck' ones. If at any point no progress can be made (no 'unstuck' nodes)
          * some inference variable might get eagerly instantiated so that all nodes
          * can be type-checked.
          */
         void complete() {
             while (!deferredAttrNodes.isEmpty()) {
                 Map<Type, Set<Type>> depVarsMap = new LinkedHashMap<Type, Set<Type>>();
                 List<Type> stuckVars = List.nil();
                 boolean progress = false;
                 //scan a defensive copy of the node list - this is because a deferred
                 //attribution round can add new nodes to the list
                 for (DeferredAttrNode deferredAttrNode : List.from(deferredAttrNodes)) {
                     if (!deferredAttrNode.process(this)) {
                         List<Type> restStuckVars =
                                 List.from(deferredAttrNode.deferredStuckPolicy.stuckVars())
                                 .intersect(inferenceContext.restvars());
                         stuckVars = stuckVars.prependList(restStuckVars);
                         //update dependency map
                         for (Type t : List.from(deferredAttrNode.deferredStuckPolicy.depVars())
                                 .intersect(inferenceContext.restvars())) {
                             Set<Type> prevDeps = depVarsMap.get(t);
                             if (prevDeps == null) {
                                 prevDeps = new LinkedHashSet<Type>();
                                 depVarsMap.put(t, prevDeps);
                             }
                             prevDeps.addAll(restStuckVars);
                         }
                     } else {
                         deferredAttrNodes.remove(deferredAttrNode);
                         progress = true;
                     }
                 }
                 if (!progress) {
                     if (insideOverloadPhase()) {
                         for (DeferredAttrNode deferredNode: deferredAttrNodes) {
                             deferredNode.dt.tree.type = Type.noType;
                         }
                         return;
                     }
                     //remove all variables that have already been instantiated
                     //from the list of stuck variables
                     try {
                         inferenceContext.solveAny(stuckVars, depVarsMap, warn);
                         inferenceContext.notifyChange();
                     } catch (Infer.GraphStrategy.NodeNotFoundException ex) {
                         //this means that we are in speculative mode and the
                         //set of contraints are too tight for progess to be made.
                         //Just leave the remaining expressions as stuck.
                         break;
                     }
                 }
             }
         }
         private boolean insideOverloadPhase() {
             DeferredAttrContext dac = this;
             if (dac == emptyDeferredAttrContext) {
                 return false;
             }
             if (dac.mode == AttrMode.SPECULATIVE) {
                 return true;
             }
             return dac.parent.insideOverloadPhase();
         }
     }
     /**
      * Class representing a deferred attribution node. It keeps track of
      * a deferred type, along with the expected target type information.
      */
     class DeferredAttrNode {
         /** underlying deferred type */
         DeferredType dt;
         /** underlying target type information */
         ResultInfo resultInfo;
         /** stuck policy associated with this node */
         DeferredStuckPolicy deferredStuckPolicy;
         DeferredAttrNode(DeferredType dt, ResultInfo resultInfo, DeferredStuckPolicy deferredStuckPolicy) {
             this.dt = dt;
             this.resultInfo = resultInfo;
             this.deferredStuckPolicy = deferredStuckPolicy;
         }
         /**
          * Process a deferred attribution node.
          * Invariant: a stuck node cannot be processed.
          */
         @SuppressWarnings("fallthrough")
         boolean process(final DeferredAttrContext deferredAttrContext) {
             switch (deferredAttrContext.mode) {
                 case SPECULATIVE:
                     if (deferredStuckPolicy.isStuck()) {
                         dt.check(resultInfo, dummyStuckPolicy, new StructuralStuckChecker());
                         return true;
                     } else {
                         Assert.error("Cannot get here");
                     }
                 case CHECK:
                     if (deferredStuckPolicy.isStuck()) {
                         //stuck expression - see if we can propagate
                         if (deferredAttrContext.parent != emptyDeferredAttrContext &&
                                 Type.containsAny(deferredAttrContext.parent.inferenceContext.inferencevars,
                                         List.from(deferredStuckPolicy.stuckVars()))) {
                             deferredAttrContext.parent.addDeferredAttrNode(dt,
                                     resultInfo.dup(new Check.NestedCheckContext(resultInfo.checkContext) {
                                 @Override
                                 public InferenceContext inferenceContext() {
                                     return deferredAttrContext.parent.inferenceContext;
                                 }
                                 @Override
                                 public DeferredAttrContext deferredAttrContext() {
                                     return deferredAttrContext.parent;
                                 }
                             }), deferredStuckPolicy);
                             dt.tree.type = Type.stuckType;
                             return true;
                         } else {
                             return false;
                         }
                     } else {
                         Assert.check(!deferredAttrContext.insideOverloadPhase(),
                                 "attribution shouldn't be happening here");
                         ResultInfo instResultInfo =
                                 resultInfo.dup(deferredAttrContext.inferenceContext.asInstType(resultInfo.pt));
                         dt.check(instResultInfo, dummyStuckPolicy, basicCompleter);
                         return true;
                     }
                 default:
                     throw new AssertionError("Bad mode");
             }
         }
         /**
          * Structural checker for stuck expressions
          */
         class StructuralStuckChecker extends TreeScanner implements DeferredTypeCompleter {
             ResultInfo resultInfo;
             InferenceContext inferenceContext;
             Env<AttrContext> env;
             public Type complete(DeferredType dt, ResultInfo resultInfo, DeferredAttrContext deferredAttrContext) {
                 this.resultInfo = resultInfo;
                 this.inferenceContext = deferredAttrContext.inferenceContext;
                 this.env = dt.env;
                 dt.tree.accept(this);
                 dt.speculativeCache.put(stuckTree, resultInfo);
                 return Type.noType;
             }
             @Override
             public void visitLambda(JCLambda tree) {
                 Check.CheckContext checkContext = resultInfo.checkContext;
                 Type pt = resultInfo.pt;
                 if (!inferenceContext.inferencevars.contains(pt)) {
                     //must be a functional descriptor
                     Type descriptorType = null;
                     try {
                         descriptorType = types.findDescriptorType(pt);
                     } catch (Types.FunctionDescriptorLookupError ex) {
                         checkContext.report(null, ex.getDiagnostic());
                     }
                     if (descriptorType.getParameterTypes().length() != tree.params.length()) {
                         checkContext.report(tree,
                                 diags.fragment("incompatible.arg.types.in.lambda"));
                     }
                     Type currentReturnType = descriptorType.getReturnType();
                     boolean returnTypeIsVoid = currentReturnType.hasTag(VOID);
                     if (tree.getBodyKind() == BodyKind.EXPRESSION) {
                         boolean isExpressionCompatible = !returnTypeIsVoid ||
                             TreeInfo.isExpressionStatement((JCExpression)tree.getBody());
                         if (!isExpressionCompatible) {
                             resultInfo.checkContext.report(tree.pos(),
                                 diags.fragment("incompatible.ret.type.in.lambda",
                                     diags.fragment("missing.ret.val", currentReturnType)));
                         }
                     } else {
                         LambdaBodyStructChecker lambdaBodyChecker =
                                 new LambdaBodyStructChecker();
                         tree.body.accept(lambdaBodyChecker);
                         boolean isVoidCompatible = lambdaBodyChecker.isVoidCompatible;
                         if (returnTypeIsVoid) {
                             if (!isVoidCompatible) {
                                 resultInfo.checkContext.report(tree.pos(),
                                     diags.fragment("unexpected.ret.val"));
                             }
                         } else {
                             boolean isValueCompatible = lambdaBodyChecker.isPotentiallyValueCompatible
                                 && !canLambdaBodyCompleteNormally(tree);
                             if (!isValueCompatible && !isVoidCompatible) {
                                 log.error(tree.body.pos(),
                                     "lambda.body.neither.value.nor.void.compatible");
                             }
                             if (!isValueCompatible) {
                                 resultInfo.checkContext.report(tree.pos(),
                                     diags.fragment("incompatible.ret.type.in.lambda",
                                         diags.fragment("missing.ret.val", currentReturnType)));
                             }
                         }
                     }
                 }
             }
             boolean canLambdaBodyCompleteNormally(JCLambda tree) {
                 JCLambda newTree = new TreeCopier<>(make).copy(tree);
                 /* attr.lambdaEnv will create a meaningful env for the
                  * lambda expression. This is specially useful when the
                  * lambda is used as the init of a field. But we need to
                  * remove any added symbol.
                  */
                 Env<AttrContext> localEnv = attr.lambdaEnv(newTree, env);
                 try {
                     List<JCVariableDecl> tmpParams = newTree.params;
                     while (tmpParams.nonEmpty()) {
                         tmpParams.head.vartype = make.at(tmpParams.head).Type(syms.errType);
                         tmpParams = tmpParams.tail;
                     }
                     attr.attribStats(newTree.params, localEnv);
                     /* set pt to Type.noType to avoid generating any bound
                      * which may happen if lambda's return type is an
                      * inference variable
                      */
                     Attr.ResultInfo bodyResultInfo = attr.new ResultInfo(VAL, Type.noType);
                     localEnv.info.returnResult = bodyResultInfo;
                     // discard any log output
                     Log.DiagnosticHandler diagHandler = new Log.DiscardDiagnosticHandler(log);
                     try {
                         JCBlock body = (JCBlock)newTree.body;
                         /* we need to attribute the lambda body before
                          * doing the aliveness analysis. This is because
                          * constant folding occurs during attribution
                          * and the reachability of some statements depends
                          * on constant values, for example:
                          *
                          *     while (true) {...}
                          */
                         attr.attribStats(body.stats, localEnv);
                         attr.preFlow(newTree);
                         /* make an aliveness / reachability analysis of the lambda
                          * to determine if it can complete normally
                          */
                         flow.analyzeLambda(localEnv, newTree, make, true);
                     } finally {
                         log.popDiagnosticHandler(diagHandler);
                     }
                     return newTree.canCompleteNormally;
                 } finally {
                     JCBlock body = (JCBlock)newTree.body;
                     unenterScanner.scan(body.stats);
                     localEnv.info.scope.leave();
                 }
             }
             @Override
             public void visitNewClass(JCNewClass tree) {
                 //do nothing
             }
             @Override
             public void visitApply(JCMethodInvocation tree) {
                 //do nothing
             }
             @Override
             public void visitReference(JCMemberReference tree) {
                 Check.CheckContext checkContext = resultInfo.checkContext;
                 Type pt = resultInfo.pt;
                 if (!inferenceContext.inferencevars.contains(pt)) {
                     try {
                         types.findDescriptorType(pt);
                     } catch (Types.FunctionDescriptorLookupError ex) {
                         checkContext.report(null, ex.getDiagnostic());
                     }
                     Env<AttrContext> localEnv = env.dup(tree);
                     JCExpression exprTree = (JCExpression)attribSpeculative(tree.getQualifierExpression(), localEnv,
                             attr.memberReferenceQualifierResult(tree));
                     ListBuffer<Type> argtypes = new ListBuffer<>();
                     for (Type t : types.findDescriptorType(pt).getParameterTypes()) {
                         argtypes.append(Type.noType);
                     }
                     JCMemberReference mref2 = new TreeCopier<Void>(make).copy(tree);
                     mref2.expr = exprTree;
                     Symbol lookupSym =
                             rs.resolveMemberReferenceByArity(localEnv, mref2, exprTree.type,
                                 tree.name, argtypes.toList(), inferenceContext);
                     switch (lookupSym.kind) {
                         //note: as argtypes are erroneous types, type-errors must
                         //have been caused by arity mismatch
                         case Kinds.ABSENT_MTH:
                         case Kinds.WRONG_MTH:
                         case Kinds.WRONG_MTHS:
                         case Kinds.WRONG_STATICNESS:
                            checkContext.report(tree, diags.fragment("incompatible.arg.types.in.mref"));
                     }
                 }
             }
         }
         /* This visitor looks for return statements, its analysis will determine if
          * a lambda body is void or value compatible. We must analyze return
          * statements contained in the lambda body only, thus any return statement
          * contained in an inner class or inner lambda body, should be ignored.
          */
         class LambdaBodyStructChecker extends TreeScanner {
             boolean isVoidCompatible = true;
             boolean isPotentiallyValueCompatible = true;
             @Override
             public void visitClassDef(JCClassDecl tree) {
                 // do nothing
             }
             @Override
             public void visitLambda(JCLambda tree) {
                 // do nothing
             }
             @Override
             public void visitNewClass(JCNewClass tree) {
                 // do nothing
             }
             @Override
             public void visitReturn(JCReturn tree) {
                 if (tree.expr != null) {
                     isVoidCompatible = false;
                 } else {
                     isPotentiallyValueCompatible = false;
                 }
             }
         }
     }
     /** an empty deferred attribution context - all methods throw exceptions */
     final DeferredAttrContext emptyDeferredAttrContext;
     /**
      * Map a list of types possibly containing one or more deferred types
      * into a list of ordinary types. Each deferred type D is mapped into a type T,
      * where T is computed by retrieving the type that has already been
      * computed for D during a previous deferred attribution round of the given kind.
      */
     class DeferredTypeMap extends Type.Mapping {
         DeferredAttrContext deferredAttrContext;
         protected DeferredTypeMap(AttrMode mode, Symbol msym, MethodResolutionPhase phase) {
             super(String.format("deferredTypeMap[%s]", mode));
             this.deferredAttrContext = new DeferredAttrContext(mode, msym, phase,
                     infer.emptyContext, emptyDeferredAttrContext, types.noWarnings);
         }
         @Override
         public Type apply(Type t) {
             if (!t.hasTag(DEFERRED)) {
                 return t.map(this);
             } else {
                 DeferredType dt = (DeferredType)t;
                 return typeOf(dt);
             }
         }
         protected Type typeOf(DeferredType dt) {
             switch (deferredAttrContext.mode) {
                 case CHECK:
                     return dt.tree.type == null ? Type.noType : dt.tree.type;
                 case SPECULATIVE:
                     return dt.speculativeType(deferredAttrContext.msym, deferredAttrContext.phase);
             }
             Assert.error();
             return null;
         }
     }
     /**
      * Specialized recovery deferred mapping.
      * Each deferred type D is mapped into a type T, where T is computed either by
      * (i) retrieving the type that has already been computed for D during a previous
      * attribution round (as before), or (ii) by synthesizing a new type R for D
      * (the latter step is useful in a recovery scenario).
      */
     public class RecoveryDeferredTypeMap extends DeferredTypeMap {
         public RecoveryDeferredTypeMap(AttrMode mode, Symbol msym, MethodResolutionPhase phase) {
             super(mode, msym, phase != null ? phase : MethodResolutionPhase.BOX);
         }
         @Override
         protected Type typeOf(DeferredType dt) {
             Type owntype = super.typeOf(dt);
             return owntype == Type.noType ?
                         recover(dt) : owntype;
         }
         /**
          * Synthesize a type for a deferred type that hasn't been previously
          * reduced to an ordinary type. Functional deferred types and conditionals
          * are mapped to themselves, in order to have a richer diagnostic
          * representation. Remaining deferred types are attributed using
          * a default expected type (j.l.Object).
          */
         private Type recover(DeferredType dt) {
             dt.check(attr.new RecoveryInfo(deferredAttrContext) {
                 @Override
                 protected Type check(DiagnosticPosition pos, Type found) {
                     return chk.checkNonVoid(pos, super.check(pos, found));
                 }
             });
             return super.apply(dt);
         }
     }
     /**
      * A special tree scanner that would only visit portions of a given tree.
      * The set of nodes visited by the scanner can be customized at construction-time.
      */
     abstract static class FilterScanner extends TreeScanner {
         final Filter<JCTree> treeFilter;
         FilterScanner(final Set<JCTree.Tag> validTags) {
             this.treeFilter = new Filter<JCTree>() {
                 public boolean accepts(JCTree t) {
                     return validTags.contains(t.getTag());
                 }
             };
         }
         @Override
         public void scan(JCTree tree) {
             if (tree != null) {
                 if (treeFilter.accepts(tree)) {
                     super.scan(tree);
                 } else {
                     skip(tree);
                 }
             }
         }
         /**
          * handler that is executed when a node has been discarded
          */
         void skip(JCTree tree) {}
     }
     /**
      * A tree scanner suitable for visiting the target-type dependent nodes of
      * a given argument expression.
      */
     static class PolyScanner extends FilterScanner {
         PolyScanner() {
             super(EnumSet.of(CONDEXPR, PARENS, LAMBDA, REFERENCE));
         }
     }
     /**
      * A tree scanner suitable for visiting the target-type dependent nodes nested
      * within a lambda expression body.
      */
     static class LambdaReturnScanner extends FilterScanner {
         LambdaReturnScanner() {
             super(EnumSet.of(BLOCK, CASE, CATCH, DOLOOP, FOREACHLOOP,
                     FORLOOP, IF, RETURN, SYNCHRONIZED, SWITCH, TRY, WHILELOOP));
         }
     }
     /**
      * This visitor is used to check that structural expressions conform
      * to their target - this step is required as inference could end up
      * inferring types that make some of the nested expressions incompatible
      * with their corresponding instantiated target
      */
     class CheckStuckPolicy extends PolyScanner implements DeferredStuckPolicy, Infer.FreeTypeListener {
         Type pt;
         Infer.InferenceContext inferenceContext;
         Set<Type> stuckVars = new LinkedHashSet<Type>();
         Set<Type> depVars = new LinkedHashSet<Type>();
         @Override
         public boolean isStuck() {
             return !stuckVars.isEmpty();
         }
         @Override
         public Set<Type> stuckVars() {
             return stuckVars;
         }
         @Override
         public Set<Type> depVars() {
             return depVars;
         }
         public CheckStuckPolicy(ResultInfo resultInfo, DeferredType dt) {
             this.pt = resultInfo.pt;
             this.inferenceContext = resultInfo.checkContext.inferenceContext();
             scan(dt.tree);
             if (!stuckVars.isEmpty()) {
                 resultInfo.checkContext.inferenceContext()
                         .addFreeTypeListener(List.from(stuckVars), this);
             }
         }
         @Override
         public void typesInferred(InferenceContext inferenceContext) {
             stuckVars.clear();
         }
         @Override
         public void visitLambda(JCLambda tree) {
             if (inferenceContext.inferenceVars().contains(pt)) {
                 stuckVars.add(pt);
             }
             if (!types.isFunctionalInterface(pt)) {
                 return;
             }
             Type descType = types.findDescriptorType(pt);
             List<Type> freeArgVars = inferenceContext.freeVarsIn(descType.getParameterTypes());
             if (tree.paramKind == JCLambda.ParameterKind.IMPLICIT &&
                     freeArgVars.nonEmpty()) {
                 stuckVars.addAll(freeArgVars);
                 depVars.addAll(inferenceContext.freeVarsIn(descType.getReturnType()));
             }
             scanLambdaBody(tree, descType.getReturnType());
         }
         @Override
         public void visitReference(JCMemberReference tree) {
             scan(tree.expr);
             if (inferenceContext.inferenceVars().contains(pt)) {
                 stuckVars.add(pt);
                 return;
             }
             if (!types.isFunctionalInterface(pt)) {
                 return;
             }
             Type descType = types.findDescriptorType(pt);
             List<Type> freeArgVars = inferenceContext.freeVarsIn(descType.getParameterTypes());
             if (freeArgVars.nonEmpty() &&
                     tree.overloadKind == JCMemberReference.OverloadKind.OVERLOADED) {
                 stuckVars.addAll(freeArgVars);
                 depVars.addAll(inferenceContext.freeVarsIn(descType.getReturnType()));
             }
         }
         void scanLambdaBody(JCLambda lambda, final Type pt) {
             if (lambda.getBodyKind() == JCTree.JCLambda.BodyKind.EXPRESSION) {
                 Type prevPt = this.pt;
                 try {
                     this.pt = pt;
                     scan(lambda.body);
                 } finally {
                     this.pt = prevPt;
                 }
             } else {
                 LambdaReturnScanner lambdaScanner = new LambdaReturnScanner() {
                     @Override
                     public void visitReturn(JCReturn tree) {
                         if (tree.expr != null) {
                             Type prevPt = CheckStuckPolicy.this.pt;
                             try {
                                 CheckStuckPolicy.this.pt = pt;
                                 CheckStuckPolicy.this.scan(tree.expr);
                             } finally {
                                 CheckStuckPolicy.this.pt = prevPt;
                             }
                         }
                     }
                 };
                 lambdaScanner.scan(lambda.body);
             }
         }
     }
     /**
      * This visitor is used to check that structural expressions conform
      * to their target - this step is required as inference could end up
      * inferring types that make some of the nested expressions incompatible
      * with their corresponding instantiated target
      */
     class OverloadStuckPolicy extends CheckStuckPolicy implements DeferredStuckPolicy {
         boolean stuck;
         @Override
         public boolean isStuck() {
             return super.isStuck() || stuck;
         }
         public OverloadStuckPolicy(ResultInfo resultInfo, DeferredType dt) {
             super(resultInfo, dt);
         }
         @Override
         public void visitLambda(JCLambda tree) {
             super.visitLambda(tree);
             if (tree.paramKind == JCLambda.ParameterKind.IMPLICIT) {
                 stuck = true;
             }
         }
         @Override
         public void visitReference(JCMemberReference tree) {
             super.visitReference(tree);
             if (tree.overloadKind == JCMemberReference.OverloadKind.OVERLOADED) {
                 stuck = true;
             }
         }
     }
     /**
      * Does the argument expression {@code expr} need speculative type-checking?
      */
     boolean isDeferred(Env<AttrContext> env, JCExpression expr) {
         DeferredChecker dc = new DeferredChecker(env);
         dc.scan(expr);
         return dc.result.isPoly();
     }
     /**
      * The kind of an argument expression. This is used by the analysis that
      * determines as to whether speculative attribution is necessary.
      */
     enum ArgumentExpressionKind {
         /** kind that denotes poly argument expression */
         POLY,
         /** kind that denotes a standalone expression */
         NO_POLY,
         /** kind that denotes a primitive/boxed standalone expression */
         PRIMITIVE;
         /**
          * Does this kind denote a poly argument expression
          */
         public final boolean isPoly() {
             return this == POLY;
         }
         /**
          * Does this kind denote a primitive standalone expression
          */
         public final boolean isPrimitive() {
             return this == PRIMITIVE;
         }
         /**
          * Compute the kind of a standalone expression of a given type
          */
         static ArgumentExpressionKind standaloneKind(Type type, Types types) {
             return types.unboxedTypeOrType(type).isPrimitive() ?
                     ArgumentExpressionKind.PRIMITIVE :
                     ArgumentExpressionKind.NO_POLY;
         }
         /**
          * Compute the kind of a method argument expression given its symbol
          */
         static ArgumentExpressionKind methodKind(Symbol sym, Types types) {
             Type restype = sym.type.getReturnType();
             if (sym.type.hasTag(FORALL) &&
                     restype.containsAny(((ForAll)sym.type).tvars)) {
                 return ArgumentExpressionKind.POLY;
             } else {
                 return ArgumentExpressionKind.standaloneKind(restype, types);
             }
         }
     }
     /**
      * Tree scanner used for checking as to whether an argument expression
      * requires speculative attribution
      */
     final class DeferredChecker extends FilterScanner {
         Env<AttrContext> env;
         ArgumentExpressionKind result;
         public DeferredChecker(Env<AttrContext> env) {
             super(deferredCheckerTags);
             this.env = env;
         }
         @Override
         public void visitLambda(JCLambda tree) {
             //a lambda is always a poly expression
             result = ArgumentExpressionKind.POLY;
         }
         @Override
         public void visitReference(JCMemberReference tree) {
             //perform arity-based check
             Env<AttrContext> localEnv = env.dup(tree);
             JCExpression exprTree = (JCExpression)attribSpeculative(tree.getQualifierExpression(), localEnv,
                     attr.memberReferenceQualifierResult(tree));
             JCMemberReference mref2 = new TreeCopier<Void>(make).copy(tree);
             mref2.expr = exprTree;
             Symbol res =
                     rs.getMemberReference(tree, localEnv, mref2,
                         exprTree.type, tree.name);
             tree.sym = res;
             if (res.kind >= Kinds.ERRONEOUS ||
                     res.type.hasTag(FORALL) ||
                     (res.flags() & Flags.VARARGS) != 0 ||
                     (TreeInfo.isStaticSelector(exprTree, tree.name.table.names) &&
                     exprTree.type.isRaw())) {
                 tree.overloadKind = JCMemberReference.OverloadKind.OVERLOADED;
             } else {
                 tree.overloadKind = JCMemberReference.OverloadKind.UNOVERLOADED;
             }
             //a method reference is always a poly expression
             result = ArgumentExpressionKind.POLY;
         }
         @Override
         public void visitTypeCast(JCTypeCast tree) {
             //a cast is always a standalone expression
             result = ArgumentExpressionKind.NO_POLY;
         }
         @Override
         public void visitConditional(JCConditional tree) {
             scan(tree.truepart);
             if (!result.isPrimitive()) {
                 result = ArgumentExpressionKind.POLY;
                 return;
             }
             scan(tree.falsepart);
             result = reduce(ArgumentExpressionKind.PRIMITIVE);
         }
         @Override
         public void visitNewClass(JCNewClass tree) {
             result = (TreeInfo.isDiamond(tree) || attr.findDiamonds) ?
                     ArgumentExpressionKind.POLY : ArgumentExpressionKind.NO_POLY;
         }
         @Override
         public void visitApply(JCMethodInvocation tree) {
             Name name = TreeInfo.name(tree.meth);
             //fast path
             if (tree.typeargs.nonEmpty() ||
                     name == name.table.names._this ||
                     name == name.table.names._super) {
                 result = ArgumentExpressionKind.NO_POLY;
                 return;
             }
             //slow path
             Symbol sym = quicklyResolveMethod(env, tree);
             if (sym == null) {
                 result = ArgumentExpressionKind.POLY;
                 return;
             }
             result = analyzeCandidateMethods(sym, ArgumentExpressionKind.PRIMITIVE,
                     argumentKindAnalyzer);
         }
         //where
             private boolean isSimpleReceiver(JCTree rec) {
                 switch (rec.getTag()) {
                     case IDENT:
                         return true;
                     case SELECT:
                         return isSimpleReceiver(((JCFieldAccess)rec).selected);
                     case TYPEAPPLY:
                     case TYPEARRAY:
                         return true;
                     case ANNOTATED_TYPE:
                         return isSimpleReceiver(((JCAnnotatedType)rec).underlyingType);
                     case APPLY:
                         return true;
                     case NEWCLASS:
                         JCNewClass nc = (JCNewClass) rec;
                         return nc.encl == null && nc.def == null && !TreeInfo.isDiamond(nc);
                     default:
                         return false;
                 }
             }
             private ArgumentExpressionKind reduce(ArgumentExpressionKind kind) {
                 return argumentKindAnalyzer.reduce(result, kind);
             }
             MethodAnalyzer<ArgumentExpressionKind> argumentKindAnalyzer =
                     new MethodAnalyzer<ArgumentExpressionKind>() {
                 @Override
                 public ArgumentExpressionKind process(MethodSymbol ms) {
                     return ArgumentExpressionKind.methodKind(ms, types);
                 }
                 @Override
                 public ArgumentExpressionKind reduce(ArgumentExpressionKind kind1,
                                                      ArgumentExpressionKind kind2) {
                     switch (kind1) {
                         case PRIMITIVE: return kind2;
                         case NO_POLY: return kind2.isPoly() ? kind2 : kind1;
                         case POLY: return kind1;
                         default:
                             Assert.error();
                             return null;
                     }
                 }
                 @Override
                 public boolean shouldStop(ArgumentExpressionKind result) {
                     return result.isPoly();
                 }
             };
         @Override
         public void visitLiteral(JCLiteral tree) {
             Type litType = attr.litType(tree.typetag);
             result = ArgumentExpressionKind.standaloneKind(litType, types);
         }
         @Override
         void skip(JCTree tree) {
             result = ArgumentExpressionKind.NO_POLY;
         }
         private Symbol quicklyResolveMethod(Env<AttrContext> env, final JCMethodInvocation tree) {
             final JCExpression rec = tree.meth.hasTag(SELECT) ?
                     ((JCFieldAccess)tree.meth).selected :
                     null;
             if (rec != null && !isSimpleReceiver(rec)) {
                 return null;
             }
             Type site;
             if (rec != null) {
                 switch (rec.getTag()) {
                     case APPLY:
                         Symbol recSym = quicklyResolveMethod(env, (JCMethodInvocation) rec);
                         if (recSym == null)
                             return null;
                         Symbol resolvedReturnType =
                                 analyzeCandidateMethods(recSym, syms.errSymbol, returnSymbolAnalyzer);
                         if (resolvedReturnType == null)
                             return null;
                         site = resolvedReturnType.type;
                         break;
                     case NEWCLASS:
                         JCNewClass nc = (JCNewClass) rec;
                         site = attribSpeculative(nc.clazz, env, attr.unknownTypeExprInfo).type;
                         break;
                     default:
                         site = attribSpeculative(rec, env, attr.unknownTypeExprInfo).type;
                         break;
                 }
             } else {
                 site = env.enclClass.sym.type;
             }
             while (site.hasTag(TYPEVAR)) {
                 site = site.getUpperBound();
             }
             site = types.capture(site);
             List<Type> args = rs.dummyArgs(tree.args.length());
             Name name = TreeInfo.name(tree.meth);
             Resolve.LookupHelper lh = rs.new LookupHelper(name, site, args, List.<Type>nil(), MethodResolutionPhase.VARARITY) {
                 @Override
                 Symbol lookup(Env<AttrContext> env, MethodResolutionPhase phase) {
                     return rec == null ?
                         rs.findFun(env, name, argtypes, typeargtypes, phase.isBoxingRequired(), phase.isVarargsRequired()) :
                         rs.findMethod(env, site, name, argtypes, typeargtypes, phase.isBoxingRequired(), phase.isVarargsRequired(), false);
                 }
                 @Override
                 Symbol access(Env<AttrContext> env, DiagnosticPosition pos, Symbol location, Symbol sym) {
                     return sym;
                 }
             };
             return rs.lookupMethod(env, tree, site.tsym, rs.arityMethodCheck, lh);
         }
         //where:
             MethodAnalyzer<Symbol> returnSymbolAnalyzer = new MethodAnalyzer<Symbol>() {
                 @Override
                 public Symbol process(MethodSymbol ms) {
                     ArgumentExpressionKind kind = ArgumentExpressionKind.methodKind(ms, types);
                     if (kind == ArgumentExpressionKind.POLY || ms.getReturnType().hasTag(TYPEVAR))
                         return null;
                     return ms.getReturnType().tsym;
                 }
                 @Override
                 public Symbol reduce(Symbol s1, Symbol s2) {
                     return s1 == syms.errSymbol ? s2 : s1 == s2 ? s1 : null;
                 }
                 @Override
                 public boolean shouldStop(Symbol result) {
                     return result == null;
                 }
             };
         /**
          * Process the result of Resolve.lookupMethod. If sym is a method symbol, the result of
          * MethodAnalyzer.process is returned. If sym is an ambiguous symbol, all the candidate
          * methods are inspected one by one, using MethodAnalyzer.process. The outcomes are
          * reduced using MethodAnalyzer.reduce (using defaultValue as the first value over which
          * the reduction runs). MethodAnalyzer.shouldStop can be used to stop the inspection early.
          */
         <E> E analyzeCandidateMethods(Symbol sym, E defaultValue, MethodAnalyzer<E> analyzer) {
             switch (sym.kind) {
                 case Kinds.MTH:
                     return analyzer.process((MethodSymbol) sym);
                 case Kinds.AMBIGUOUS:
                     Resolve.AmbiguityError err = (Resolve.AmbiguityError)sym.baseSymbol();
                     E res = defaultValue;
                     for (Symbol s : err.ambiguousSyms) {
                         if (s.kind == Kinds.MTH) {
                             res = analyzer.reduce(res, analyzer.process((MethodSymbol) s));
                             if (analyzer.shouldStop(res))
                                 return res;
                         }
                     }
                     return res;
                 default:
                     return defaultValue;
             }
         }
     }
     /** Analyzer for methods - used by analyzeCandidateMethods. */
     interface MethodAnalyzer<E> {
         E process(MethodSymbol ms);
         E reduce(E e1, E e2);
         boolean shouldStop(E result);
     }
     //where
     private EnumSet<JCTree.Tag> deferredCheckerTags =
             EnumSet.of(LAMBDA, REFERENCE, PARENS, TYPECAST,
                     CONDEXPR, NEWCLASS, APPLY, LITERAL);
 }

Mercurial > jdk8-mips64-public > langtools / annotate

src/share/classes/com/sun/tools/javac/comp/DeferredAttr.java@ca5783d9a597 (annotated)

src/share/classes/com/sun/tools/javac/comp/DeferredAttr.java