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src/jdk/nashorn/internal/runtime/ConsString.java@abea4ba28901 (annotated)

src/jdk/nashorn/internal/runtime/ConsString.java

Mon, 11 Feb 2013 21:26:06 +0530

author

sundar

date

Mon, 11 Feb 2013 21:26:06 +0530

changeset 82

abea4ba28901

parent 7

5a1b0714df0e

child 663

98bab0cdd7bf

permissions

-rw-r--r--

8007915: Nashorn IR, codegen, parser packages and Context instance should be inaccessible to user code
Reviewed-by: lagergren, jlaskey, attila

jlaskey@3	1	/*
jlaskey@7	2	* Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved.
jlaskey@3	3	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
jlaskey@3	4	*
jlaskey@3	5	* This code is free software; you can redistribute it and/or modify it
jlaskey@3	6	* under the terms of the GNU General Public License version 2 only, as
jlaskey@3	7	* published by the Free Software Foundation. Oracle designates this
jlaskey@3	8	* particular file as subject to the "Classpath" exception as provided
jlaskey@3	9	* by Oracle in the LICENSE file that accompanied this code.
jlaskey@3	10	*
jlaskey@3	11	* This code is distributed in the hope that it will be useful, but WITHOUT
jlaskey@3	12	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
jlaskey@3	13	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
jlaskey@3	14	* version 2 for more details (a copy is included in the LICENSE file that
jlaskey@3	15	* accompanied this code).
jlaskey@3	16	*
jlaskey@3	17	* You should have received a copy of the GNU General Public License version
jlaskey@3	18	* 2 along with this work; if not, write to the Free Software Foundation,
jlaskey@3	19	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
jlaskey@3	20	*
jlaskey@3	21	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
jlaskey@3	22	* or visit www.oracle.com if you need additional information or have any
jlaskey@3	23	* questions.
jlaskey@3	24	*/
jlaskey@3	25
jlaskey@3	26	package jdk.nashorn.internal.runtime;
jlaskey@3	27
jlaskey@3	28	import java.util.ArrayDeque;
jlaskey@3	29	import java.util.Deque;
jlaskey@3	30
jlaskey@3	31	/**
jlaskey@3	32	* This class represents a string composed of two parts which may themselves be
jlaskey@3	33	* instances of <tt>ConsString</tt> or {@link String}. Copying of characters to
jlaskey@3	34	* a proper string is delayed until it becomes necessary.
jlaskey@3	35	*/
sundar@82	36	public final class ConsString implements CharSequence {
jlaskey@3	37
jlaskey@3	38	private CharSequence left, right;
jlaskey@3	39	final private int length;
jlaskey@3	40	private boolean flat = false;
jlaskey@3	41
jlaskey@3	42	/**
jlaskey@3	43	* Constructor
jlaskey@3	44	*
jlaskey@3	45	* Takes two {@link CharSequence} instances that, concatenated, forms this {@code ConsString}
jlaskey@3	46	*
jlaskey@3	47	* @param left left char sequence
jlaskey@3	48	* @param right right char sequence
jlaskey@3	49	*/
jlaskey@3	50	public ConsString(final CharSequence left, final CharSequence right) {
jlaskey@3	51	assert left instanceof String || left instanceof ConsString;
jlaskey@3	52	assert right instanceof String || right instanceof ConsString;
jlaskey@3	53	this.left = left;
jlaskey@3	54	this.right = right;
jlaskey@3	55	length = left.length() + right.length();
jlaskey@3	56	}
jlaskey@3	57
jlaskey@3	58	@Override
jlaskey@3	59	public String toString() {
jlaskey@3	60	if (!flat) {
jlaskey@3	61	flatten();
jlaskey@3	62	}
jlaskey@3	63	return (String) left;
jlaskey@3	64	}
jlaskey@3	65
jlaskey@3	66	@Override
jlaskey@3	67	public int length() {
jlaskey@3	68	return length;
jlaskey@3	69	}
jlaskey@3	70
jlaskey@3	71	@Override
jlaskey@3	72	public char charAt(final int index) {
jlaskey@3	73	if (!flat) {
jlaskey@3	74	flatten();
jlaskey@3	75	}
jlaskey@3	76	return left.charAt(index);
jlaskey@3	77	}
jlaskey@3	78
jlaskey@3	79	@Override
jlaskey@3	80	public CharSequence subSequence(final int start, final int end) {
jlaskey@3	81	if (!flat) {
jlaskey@3	82	flatten();
jlaskey@3	83	}
jlaskey@3	84	return left.subSequence(start, end);
jlaskey@3	85	}
jlaskey@3	86
jlaskey@3	87	private void flatten() {
jlaskey@3	88	// We use iterative traversal as recursion may exceed the stack size limit.
jlaskey@3	89	final char[] chars = new char[length];
jlaskey@3	90	int pos = length;
jlaskey@3	91	// Strings are most often composed by appending to the end, which causes ConsStrings
jlaskey@3	92	// to be very unbalanced, with mostly single string elements on the right and a long
jlaskey@3	93	// linear list on the left. Traversing from right to left helps to keep the stack small
jlaskey@3	94	// in this scenario.
jlaskey@3	95	final Deque<CharSequence> stack = new ArrayDeque<>();
jlaskey@3	96	stack.addFirst(left);
jlaskey@3	97	CharSequence cs = right;
jlaskey@3	98
jlaskey@3	99	do {
jlaskey@3	100	if (cs instanceof ConsString) {
jlaskey@3	101	final ConsString cons = (ConsString) cs;
jlaskey@3	102	stack.addFirst(cons.left);
jlaskey@3	103	cs = cons.right;
jlaskey@3	104	} else {
jlaskey@3	105	final String str = (String) cs;
jlaskey@3	106	pos -= str.length();
jlaskey@3	107	str.getChars(0, str.length(), chars, pos);
jlaskey@3	108	cs = stack.isEmpty() ? null : stack.pollFirst();
jlaskey@3	109	}
jlaskey@3	110	} while (cs != null);
jlaskey@3	111
jlaskey@3	112	left = new String(chars);
jlaskey@3	113	right = "";
jlaskey@3	114	flat = true;
jlaskey@3	115	}
jlaskey@3	116
jlaskey@3	117	}