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 /*

  * Copyright (c) 1999, 2006, 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.util;

 import java.lang.reflect.Array;

 import java.util.ArrayList;

 import java.util.Collection;

 import java.util.Collections;

 import java.util.Iterator;

 import java.util.AbstractCollection;

 import java.util.ListIterator;

 import java.util.NoSuchElementException;

 /** A class for generic linked lists. Links are supposed to be

  *  immutable, the only exception being the incremental construction of

  *  lists via ListBuffers.  List is the main container class in

  *  GJC. Most data structures and algorthms in GJC use lists rather

  *  than arrays.

  *

  *  <p>Lists are always trailed by a sentinel element, whose head and tail

  *  are both null.

  *

  *  <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 List<A> extends AbstractCollection<A> implements java.util.List<A> {

     /** The first element of the list, supposed to be immutable.

      */

     public A head;

     /** The remainder of the list except for its first element, supposed

      *  to be immutable.

      */

     //@Deprecated

     public List<A> tail;

     /** Construct a list given its head and tail.

      */

     List(A head, List<A> tail) {

         this.tail = tail;

         this.head = head;

     }

     /** Construct an empty list.

      */

     @SuppressWarnings("unchecked")

     public static <A> List<A> nil() {

         return (List<A>)EMPTY_LIST;

     }

     private static List<?> EMPTY_LIST = new List<Object>(null,null) {

         public List<Object> setTail(List<Object> tail) {

             throw new UnsupportedOperationException();

         }

         public boolean isEmpty() {

             return true;

         }

     };

     /** Construct a list consisting of given element.

      */

     public static <A> List<A> of(A x1) {

         return new List<A>(x1, List.<A>nil());

     }

     /** Construct a list consisting of given elements.

      */

     public static <A> List<A> of(A x1, A x2) {

         return new List<A>(x1, of(x2));

     }

     /** Construct a list consisting of given elements.

      */

     public static <A> List<A> of(A x1, A x2, A x3) {

         return new List<A>(x1, of(x2, x3));

     }

     /** Construct a list consisting of given elements.

      */

     @SuppressWarnings("varargs")

     public static <A> List<A> of(A x1, A x2, A x3, A... rest) {

         return new List<A>(x1, new List<A>(x2, new List<A>(x3, from(rest))));

     }

     /**

      * Construct a list consisting all elements of given array.

      * @param array an array; if {@code null} return an empty list

      */

     public static <A> List<A> from(A[] array) {

         List<A> xs = nil();

         if (array != null)

             for (int i = array.length - 1; i >= 0; i--)

                 xs = new List<A>(array[i], xs);

         return xs;

     }

     /** Construct a list consisting of a given number of identical elements.

      *  @param len    The number of elements in the list.

      *  @param init   The value of each element.

      */

     @Deprecated

     public static <A> List<A> fill(int len, A init) {

         List<A> l = nil();

         for (int i = 0; i < len; i++) l = new List<A>(init, l);

         return l;

     }

     /** Does list have no elements?

      */

     @Override

     public boolean isEmpty() {

         return tail == null;

     }

     /** Does list have elements?

      */

     //@Deprecated

     public boolean nonEmpty() {

         return tail != null;

     }

     /** Return the number of elements in this list.

      */

     //@Deprecated

     public int length() {

         List<A> l = this;

         int len = 0;

         while (l.tail != null) {

             l = l.tail;

             len++;

         }

         return len;

     }

     @Override

     public int size() {

         return length();

     }

     public List<A> setTail(List<A> tail) {

         this.tail = tail;

         return tail;

     }

     /** Prepend given element to front of list, forming and returning

      *  a new list.

      */

     public List<A> prepend(A x) {

         return new List<A>(x, this);

     }

     /** Prepend given list of elements to front of list, forming and returning

      *  a new list.

      */

     public List<A> prependList(List<A> xs) {

         if (this.isEmpty()) return xs;

         if (xs.isEmpty()) return this;

         if (xs.tail.isEmpty()) return prepend(xs.head);

         // return this.prependList(xs.tail).prepend(xs.head);

         List<A> result = this;

         List<A> rev = xs.reverse();

         assert rev != xs;

         // since xs.reverse() returned a new list, we can reuse the

         // individual List objects, instead of allocating new ones.

         while (rev.nonEmpty()) {

             List<A> h = rev;

             rev = rev.tail;

             h.setTail(result);

             result = h;

         }

         return result;

     }

     /** Reverse list.

      * If the list is empty or a singleton, then the same list is returned.

      * Otherwise a new list is formed.

      */

     public List<A> reverse() {

         // if it is empty or a singleton, return itself

         if (isEmpty() || tail.isEmpty())

             return this;

         List<A> rev = nil();

         for (List<A> l = this; l.nonEmpty(); l = l.tail)

             rev = new List<A>(l.head, rev);

         return rev;

     }

     /** Append given element at length, forming and returning

      *  a new list.

      */

     public List<A> append(A x) {

         return of(x).prependList(this);

     }

     /** Append given list at length, forming and returning

      *  a new list.

      */

     public List<A> appendList(List<A> x) {

         return x.prependList(this);

     }

     /**

      * Append given list buffer at length, forming and returning a new

      * list.

      */

     public List<A> appendList(ListBuffer<A> x) {

         return appendList(x.toList());

     }

     /** Copy successive elements of this list into given vector until

      *  list is exhausted or end of vector is reached.

      */

     @Override @SuppressWarnings("unchecked")

     public <T> T[] toArray(T[] vec) {

         int i = 0;

         List<A> l = this;

         Object[] dest = vec;

         while (l.nonEmpty() && i < vec.length) {

             dest[i] = l.head;

             l = l.tail;

             i++;

         }

         if (l.isEmpty()) {

             if (i < vec.length)

                 vec[i] = null;

             return vec;

         }

         vec = (T[])Array.newInstance(vec.getClass().getComponentType(), size());

         return toArray(vec);

     }

     public Object[] toArray() {

         return toArray(new Object[size()]);

     }

     /** Form a string listing all elements with given separator character.

      */

     public String toString(String sep) {

         if (isEmpty()) {

             return "";

         } else {

             StringBuffer buf = new StringBuffer();

             buf.append(head);

             for (List<A> l = tail; l.nonEmpty(); l = l.tail) {

                 buf.append(sep);

                 buf.append(l.head);

             }

             return buf.toString();

         }

     }

     /** Form a string listing all elements with comma as the separator character.

      */

     @Override

     public String toString() {

         return toString(",");

     }

     /** Compute a hash code, overrides Object

      *  @see java.util.List#hashCode

      */

     @Override

     public int hashCode() {

         List<A> l = this;

         int h = 1;

         while (l.tail != null) {

             h = h * 31 + (l.head == null ? 0 : l.head.hashCode());

             l = l.tail;

         }

         return h;

     }

     /** Is this list the same as other list?

      *  @see java.util.List#equals

      */

     @Override

     public boolean equals(Object other) {

         if (other instanceof List<?>)

             return equals(this, (List<?>)other);

         if (other instanceof java.util.List<?>) {

             List<A> t = this;

             Iterator<?> oIter = ((java.util.List<?>) other).iterator();

             while (t.tail != null && oIter.hasNext()) {

                 Object o = oIter.next();

                 if ( !(t.head == null ? o == null : t.head.equals(o)))

                     return false;

                 t = t.tail;

             }

             return (t.isEmpty() && !oIter.hasNext());

         }

         return false;

     }

     /** Are the two lists the same?

      */

     public static boolean equals(List<?> xs, List<?> ys) {

         while (xs.tail != null && ys.tail != null) {

             if (xs.head == null) {

                 if (ys.head != null) return false;

             } else {

                 if (!xs.head.equals(ys.head)) return false;

             }

             xs = xs.tail;

             ys = ys.tail;

         }

         return xs.tail == null && ys.tail == null;

     }

     /** Does the list contain the specified element?

      */

     @Override

     public boolean contains(Object x) {

         List<A> l = this;

         while (l.tail != null) {

             if (x == null) {

                 if (l.head == null) return true;

             } else {

                 if (l.head.equals(x)) return true;

             }

             l = l.tail;

         }

         return false;

     }

     /** The last element in the list, if any, or null.

      */

     public A last() {

         A last = null;

         List<A> t = this;

         while (t.tail != null) {

             last = t.head;

             t = t.tail;

         }

         return last;

     }

     @SuppressWarnings("unchecked")

     public static <T> List<T> convert(Class<T> klass, List<?> list) {

         if (list == null)

             return null;

         for (Object o : list)

             klass.cast(o);

         return (List<T>)list;

     }

     private static Iterator<?> EMPTYITERATOR = new Iterator<Object>() {

             public boolean hasNext() {

                 return false;

             }

             public Object next() {

                 throw new java.util.NoSuchElementException();

             }

             public void remove() {

                 throw new UnsupportedOperationException();

             }

         };

     @SuppressWarnings("unchecked")

     private static <A> Iterator<A> emptyIterator() {

         return (Iterator<A>)EMPTYITERATOR;

     }

     @Override

     public Iterator<A> iterator() {

         if (tail == null)

             return emptyIterator();

         return new Iterator<A>() {

             List<A> elems = List.this;

             public boolean hasNext() {

                 return elems.tail != null;

             }

             public A next() {

                 if (elems.tail == null)

                     throw new NoSuchElementException();

                 A result = elems.head;

                 elems = elems.tail;

                 return result;

             }

             public void remove() {

                 throw new UnsupportedOperationException();

             }

         };

     }

     public A get(int index) {

         if (index < 0)

             throw new IndexOutOfBoundsException(String.valueOf(index));

         List<A> l = this;

         for (int i = index; i-- > 0 && !l.isEmpty(); l = l.tail)

             ;

         if (l.isEmpty())

             throw new IndexOutOfBoundsException("Index: " + index + ", " +

                                                 "Size: " + size());

         return l.head;

     }

     public boolean addAll(int index, Collection<? extends A> c) {

         if (c.isEmpty())

             return false;

         throw new UnsupportedOperationException();

     }

     public A set(int index, A element) {

         throw new UnsupportedOperationException();

     }

     public void add(int index, A element) {

         throw new UnsupportedOperationException();

     }

     public A remove(int index) {

         throw new UnsupportedOperationException();

     }

     public int indexOf(Object o) {

         int i = 0;

         for (List<A> l = this; l.tail != null; l = l.tail, i++) {

             if (l.head == null ? o == null : l.head.equals(o))

                 return i;

         }

         return -1;

     }

     public int lastIndexOf(Object o) {

         int last = -1;

         int i = 0;

         for (List<A> l = this; l.tail != null; l = l.tail, i++) {

             if (l.head == null ? o == null : l.head.equals(o))

                 last = i;

         }

         return last;

     }

     public ListIterator<A> listIterator() {

         return Collections.unmodifiableList(new ArrayList<A>(this)).listIterator();

     }

     public ListIterator<A> listIterator(int index) {

         return Collections.unmodifiableList(new ArrayList<A>(this)).listIterator(index);

     }

     public java.util.List<A> subList(int fromIndex, int toIndex) {

         if  (fromIndex < 0 || toIndex > size() || fromIndex > toIndex)

             throw new IllegalArgumentException();

         ArrayList<A> a = new ArrayList<A>(toIndex - fromIndex);

         int i = 0;

         for (List<A> l = this; l.tail != null; l = l.tail, i++) {

             if (i == toIndex)

                 break;

             if (i >= fromIndex)

                 a.add(l.head);

         }

         return Collections.unmodifiableList(a);

     }

 }