Java tutorial
/* * Copyright (c) 1994, 2019, 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 java.lang; import java.util.Arrays; import jdk.internal.HotSpotIntrinsicCandidate; /** * A thread-safe, mutable sequence of characters. * A string buffer is like a {@link String}, but can be modified. At any * point in time it contains some particular sequence of characters, but * the length and content of the sequence can be changed through certain * method calls. * <p> * String buffers are safe for use by multiple threads. The methods * are synchronized where necessary so that all the operations on any * particular instance behave as if they occur in some serial order * that is consistent with the order of the method calls made by each of * the individual threads involved. * <p> * The principal operations on a {@code StringBuffer} are the * {@code append} and {@code insert} methods, which are * overloaded so as to accept data of any type. Each effectively * converts a given datum to a string and then appends or inserts the * characters of that string to the string buffer. The * {@code append} method always adds these characters at the end * of the buffer; the {@code insert} method adds the characters at * a specified point. * <p> * For example, if {@code z} refers to a string buffer object * whose current contents are {@code "start"}, then * the method call {@code z.append("le")} would cause the string * buffer to contain {@code "startle"}, whereas * {@code z.insert(4, "le")} would alter the string buffer to * contain {@code "starlet"}. * <p> * In general, if sb refers to an instance of a {@code StringBuffer}, * then {@code sb.append(x)} has the same effect as * {@code sb.insert(sb.length(), x)}. * <p> * Whenever an operation occurs involving a source sequence (such as * appending or inserting from a source sequence), this class synchronizes * only on the string buffer performing the operation, not on the source. * Note that while {@code StringBuffer} is designed to be safe to use * concurrently from multiple threads, if the constructor or the * {@code append} or {@code insert} operation is passed a source sequence * that is shared across threads, the calling code must ensure * that the operation has a consistent and unchanging view of the source * sequence for the duration of the operation. * This could be satisfied by the caller holding a lock during the * operation's call, by using an immutable source sequence, or by not * sharing the source sequence across threads. * <p> * Every string buffer has a capacity. As long as the length of the * character sequence contained in the string buffer does not exceed * the capacity, it is not necessary to allocate a new internal * buffer array. If the internal buffer overflows, it is * automatically made larger. * <p> * Unless otherwise noted, passing a {@code null} argument to a constructor * or method in this class will cause a {@link NullPointerException} to be * thrown. * <p> * As of release JDK 5, this class has been supplemented with an equivalent * class designed for use by a single thread, {@link StringBuilder}. The * {@code StringBuilder} class should generally be used in preference to * this one, as it supports all of the same operations but it is faster, as * it performs no synchronization. * * @apiNote * {@code StringBuffer} implements {@code Comparable} but does not override * {@link Object#equals equals}. Thus, the natural ordering of {@code StringBuffer} * is inconsistent with equals. Care should be exercised if {@code StringBuffer} * objects are used as keys in a {@code SortedMap} or elements in a {@code SortedSet}. * See {@link Comparable}, {@link java.util.SortedMap SortedMap}, or * {@link java.util.SortedSet SortedSet} for more information. * * @author Arthur van Hoff * @see java.lang.StringBuilder * @see java.lang.String * @since 1.0 */ public final class StringBuffer extends AbstractStringBuilder implements java.io.Serializable, Comparable<StringBuffer>, CharSequence { /** * A cache of the last value returned by toString. Cleared * whenever the StringBuffer is modified. */ private transient String toStringCache; /** use serialVersionUID from JDK 1.0.2 for interoperability */ static final long serialVersionUID = 3388685877147921107L; /** * Constructs a string buffer with no characters in it and an * initial capacity of 16 characters. */ @HotSpotIntrinsicCandidate public StringBuffer() { super(16); } /** * Constructs a string buffer with no characters in it and * the specified initial capacity. * * @param capacity the initial capacity. * @throws NegativeArraySizeException if the {@code capacity} * argument is less than {@code 0}. */ @HotSpotIntrinsicCandidate public StringBuffer(int capacity) { super(capacity); } /** * Constructs a string buffer initialized to the contents of the * specified string. The initial capacity of the string buffer is * {@code 16} plus the length of the string argument. * * @param str the initial contents of the buffer. */ @HotSpotIntrinsicCandidate public StringBuffer(String str) { super(str); } /** * Constructs a string buffer that contains the same characters * as the specified {@code CharSequence}. The initial capacity of * the string buffer is {@code 16} plus the length of the * {@code CharSequence} argument. * * @param seq the sequence to copy. * @since 1.5 */ public StringBuffer(CharSequence seq) { super(seq); } /** * Compares two {@code StringBuffer} instances lexicographically. This method * follows the same rules for lexicographical comparison as defined in the * {@linkplain java.lang.CharSequence#compare(java.lang.CharSequence, * java.lang.CharSequence) CharSequence.compare(this, another)} method. * * <p> * For finer-grained, locale-sensitive String comparison, refer to * {@link java.text.Collator}. * * @implNote * This method synchronizes on {@code this}, the current object, but not * {@code StringBuffer another} with which {@code this StringBuffer} is compared. * * @param another the {@code StringBuffer} to be compared with * * @return the value {@code 0} if this {@code StringBuffer} contains the same * character sequence as that of the argument {@code StringBuffer}; a negative integer * if this {@code StringBuffer} is lexicographically less than the * {@code StringBuffer} argument; or a positive integer if this {@code StringBuffer} * is lexicographically greater than the {@code StringBuffer} argument. * * @since 11 */ @Override public synchronized int compareTo(StringBuffer another) { return super.compareTo(another); } @Override public synchronized int length() { return count; } @Override public synchronized int capacity() { return super.capacity(); } @Override public synchronized void ensureCapacity(int minimumCapacity) { super.ensureCapacity(minimumCapacity); } /** * @since 1.5 */ @Override public synchronized void trimToSize() { super.trimToSize(); } /** * @throws IndexOutOfBoundsException {@inheritDoc} * @see #length() */ @Override public synchronized void setLength(int newLength) { toStringCache = null; super.setLength(newLength); } /** * @throws IndexOutOfBoundsException {@inheritDoc} * @see #length() */ @Override public synchronized char charAt(int index) { return super.charAt(index); } /** * @throws IndexOutOfBoundsException {@inheritDoc} * @since 1.5 */ @Override public synchronized int codePointAt(int index) { return super.codePointAt(index); } /** * @throws IndexOutOfBoundsException {@inheritDoc} * @since 1.5 */ @Override public synchronized int codePointBefore(int index) { return super.codePointBefore(index); } /** * @throws IndexOutOfBoundsException {@inheritDoc} * @since 1.5 */ @Override public synchronized int codePointCount(int beginIndex, int endIndex) { return super.codePointCount(beginIndex, endIndex); } /** * @throws IndexOutOfBoundsException {@inheritDoc} * @since 1.5 */ @Override public synchronized int offsetByCodePoints(int index, int codePointOffset) { return super.offsetByCodePoints(index, codePointOffset); } /** * @throws IndexOutOfBoundsException {@inheritDoc} */ @Override public synchronized void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin) { super.getChars(srcBegin, srcEnd, dst, dstBegin); } /** * @throws IndexOutOfBoundsException {@inheritDoc} * @see #length() */ @Override public synchronized void setCharAt(int index, char ch) { toStringCache = null; super.setCharAt(index, ch); } @Override public synchronized StringBuffer append(Object obj) { toStringCache = null; super.append(String.valueOf(obj)); return this; } @Override @HotSpotIntrinsicCandidate public synchronized StringBuffer append(String str) { toStringCache = null; super.append(str); return this; } /** * Appends the specified {@code StringBuffer} to this sequence. * <p> * The characters of the {@code StringBuffer} argument are appended, * in order, to the contents of this {@code StringBuffer}, increasing the * length of this {@code StringBuffer} by the length of the argument. * If {@code sb} is {@code null}, then the four characters * {@code "null"} are appended to this {@code StringBuffer}. * <p> * Let <i>n</i> be the length of the old character sequence, the one * contained in the {@code StringBuffer} just prior to execution of the * {@code append} method. Then the character at index <i>k</i> in * the new character sequence is equal to the character at index <i>k</i> * in the old character sequence, if <i>k</i> is less than <i>n</i>; * otherwise, it is equal to the character at index <i>k-n</i> in the * argument {@code sb}. * <p> * This method synchronizes on {@code this}, the destination * object, but does not synchronize on the source ({@code sb}). * * @param sb the {@code StringBuffer} to append. * @return a reference to this object. * @since 1.4 */ public synchronized StringBuffer append(StringBuffer sb) { toStringCache = null; super.append(sb); return this; } /** * @since 1.8 */ @Override synchronized StringBuffer append(AbstractStringBuilder asb) { toStringCache = null; super.append(asb); return this; } /** * Appends the specified {@code CharSequence} to this * sequence. * <p> * The characters of the {@code CharSequence} argument are appended, * in order, increasing the length of this sequence by the length of the * argument. * * <p>The result of this method is exactly the same as if it were an * invocation of this.append(s, 0, s.length()); * * <p>This method synchronizes on {@code this}, the destination * object, but does not synchronize on the source ({@code s}). * * <p>If {@code s} is {@code null}, then the four characters * {@code "null"} are appended. * * @param s the {@code CharSequence} to append. * @return a reference to this object. * @since 1.5 */ @Override public synchronized StringBuffer append(CharSequence s) { toStringCache = null; super.append(s); return this; } /** * @throws IndexOutOfBoundsException {@inheritDoc} * @since 1.5 */ @Override public synchronized StringBuffer append(CharSequence s, int start, int end) { toStringCache = null; super.append(s, start, end); return this; } @Override public synchronized StringBuffer append(char[] str) { toStringCache = null; super.append(str); return this; } /** * @throws IndexOutOfBoundsException {@inheritDoc} */ @Override public synchronized StringBuffer append(char[] str, int offset, int len) { toStringCache = null; super.append(str, offset, len); return this; } @Override public synchronized StringBuffer append(boolean b) { toStringCache = null; super.append(b); return this; } @Override @HotSpotIntrinsicCandidate public synchronized StringBuffer append(char c) { toStringCache = null; super.append(c); return this; } @Override @HotSpotIntrinsicCandidate public synchronized StringBuffer append(int i) { toStringCache = null; super.append(i); return this; } /** * @since 1.5 */ @Override public synchronized StringBuffer appendCodePoint(int codePoint) { toStringCache = null; super.appendCodePoint(codePoint); return this; } @Override public synchronized StringBuffer append(long lng) { toStringCache = null; super.append(lng); return this; } @Override public synchronized StringBuffer append(float f) { toStringCache = null; super.append(f); return this; } @Override public synchronized StringBuffer append(double d) { toStringCache = null; super.append(d); return this; } /** * @throws StringIndexOutOfBoundsException {@inheritDoc} * @since 1.2 */ @Override public synchronized StringBuffer delete(int start, int end) { toStringCache = null; super.delete(start, end); return this; } /** * @throws StringIndexOutOfBoundsException {@inheritDoc} * @since 1.2 */ @Override public synchronized StringBuffer deleteCharAt(int index) { toStringCache = null; super.deleteCharAt(index); return this; } /** * @throws StringIndexOutOfBoundsException {@inheritDoc} * @since 1.2 */ @Override public synchronized StringBuffer replace(int start, int end, String str) { toStringCache = null; super.replace(start, end, str); return this; } /** * @throws StringIndexOutOfBoundsException {@inheritDoc} * @since 1.2 */ @Override public synchronized String substring(int start) { return substring(start, count); } /** * @throws IndexOutOfBoundsException {@inheritDoc} * @since 1.4 */ @Override public synchronized CharSequence subSequence(int start, int end) { return super.substring(start, end); } /** * @throws StringIndexOutOfBoundsException {@inheritDoc} * @since 1.2 */ @Override public synchronized String substring(int start, int end) { return super.substring(start, end); } /** * @throws StringIndexOutOfBoundsException {@inheritDoc} * @since 1.2 */ @Override public synchronized StringBuffer insert(int index, char[] str, int offset, int len) { toStringCache = null; super.insert(index, str, offset, len); return this; } /** * @throws StringIndexOutOfBoundsException {@inheritDoc} */ @Override public synchronized StringBuffer insert(int offset, Object obj) { toStringCache = null; super.insert(offset, String.valueOf(obj)); return this; } /** * @throws StringIndexOutOfBoundsException {@inheritDoc} */ @Override public synchronized StringBuffer insert(int offset, String str) { toStringCache = null; super.insert(offset, str); return this; } /** * @throws StringIndexOutOfBoundsException {@inheritDoc} */ @Override public synchronized StringBuffer insert(int offset, char[] str) { toStringCache = null; super.insert(offset, str); return this; } /** * @throws IndexOutOfBoundsException {@inheritDoc} * @since 1.5 */ @Override public StringBuffer insert(int dstOffset, CharSequence s) { // Note, synchronization achieved via invocations of other StringBuffer methods // after narrowing of s to specific type // Ditto for toStringCache clearing super.insert(dstOffset, s); return this; } /** * @throws IndexOutOfBoundsException {@inheritDoc} * @since 1.5 */ @Override public synchronized StringBuffer insert(int dstOffset, CharSequence s, int start, int end) { toStringCache = null; super.insert(dstOffset, s, start, end); return this; } /** * @throws StringIndexOutOfBoundsException {@inheritDoc} */ @Override public StringBuffer insert(int offset, boolean b) { // Note, synchronization achieved via invocation of StringBuffer insert(int, String) // after conversion of b to String by super class method // Ditto for toStringCache clearing super.insert(offset, b); return this; } /** * @throws IndexOutOfBoundsException {@inheritDoc} */ @Override public synchronized StringBuffer insert(int offset, char c) { toStringCache = null; super.insert(offset, c); return this; } /** * @throws StringIndexOutOfBoundsException {@inheritDoc} */ @Override public StringBuffer insert(int offset, int i) { // Note, synchronization achieved via invocation of StringBuffer insert(int, String) // after conversion of i to String by super class method // Ditto for toStringCache clearing super.insert(offset, i); return this; } /** * @throws StringIndexOutOfBoundsException {@inheritDoc} */ @Override public StringBuffer insert(int offset, long l) { // Note, synchronization achieved via invocation of StringBuffer insert(int, String) // after conversion of l to String by super class method // Ditto for toStringCache clearing super.insert(offset, l); return this; } /** * @throws StringIndexOutOfBoundsException {@inheritDoc} */ @Override public StringBuffer insert(int offset, float f) { // Note, synchronization achieved via invocation of StringBuffer insert(int, String) // after conversion of f to String by super class method // Ditto for toStringCache clearing super.insert(offset, f); return this; } /** * @throws StringIndexOutOfBoundsException {@inheritDoc} */ @Override public StringBuffer insert(int offset, double d) { // Note, synchronization achieved via invocation of StringBuffer insert(int, String) // after conversion of d to String by super class method // Ditto for toStringCache clearing super.insert(offset, d); return this; } /** * @since 1.4 */ @Override public int indexOf(String str) { // Note, synchronization achieved via invocations of other StringBuffer methods return super.indexOf(str); } /** * @since 1.4 */ @Override public synchronized int indexOf(String str, int fromIndex) { return super.indexOf(str, fromIndex); } /** * @since 1.4 */ @Override public int lastIndexOf(String str) { // Note, synchronization achieved via invocations of other StringBuffer methods return lastIndexOf(str, count); } /** * @since 1.4 */ @Override public synchronized int lastIndexOf(String str, int fromIndex) { return super.lastIndexOf(str, fromIndex); } /** * @since 1.0.2 */ @Override public synchronized StringBuffer reverse() { toStringCache = null; super.reverse(); return this; } @Override @HotSpotIntrinsicCandidate public synchronized String toString() { if (toStringCache == null) { return toStringCache = isLatin1() ? StringLatin1.newString(value, 0, count) : StringUTF16.newString(value, 0, count); } return new String(toStringCache); } /** * Serializable fields for StringBuffer. * * @serialField value char[] * The backing character array of this StringBuffer. * @serialField count int * The number of characters in this StringBuffer. * @serialField shared boolean * A flag indicating whether the backing array is shared. * The value is ignored upon deserialization. */ private static final java.io.ObjectStreamField[] serialPersistentFields = { new java.io.ObjectStreamField("value", char[].class), new java.io.ObjectStreamField("count", Integer.TYPE), new java.io.ObjectStreamField("shared", Boolean.TYPE), }; /** * readObject is called to restore the state of the StringBuffer from * a stream. */ private synchronized void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException { java.io.ObjectOutputStream.PutField fields = s.putFields(); char[] val = new char[capacity()]; if (isLatin1()) { StringLatin1.getChars(value, 0, count, val, 0); } else { StringUTF16.getChars(value, 0, count, val, 0); } fields.put("value", val); fields.put("count", count); fields.put("shared", false); s.writeFields(); } /** * readObject is called to restore the state of the StringBuffer from * a stream. */ private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException { java.io.ObjectInputStream.GetField fields = s.readFields(); char[] val = (char[]) fields.get("value", null); initBytes(val, 0, val.length); count = fields.get("count", 0); } synchronized void getBytes(byte dst[], int dstBegin, byte coder) { super.getBytes(dst, dstBegin, coder); } }