stringbuffer.java

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/*
 * @(#)StringBuffer.java	1.36 98/10/28
 *
 * Copyright 1995-1998 by Sun Microsystems, Inc.,
 * 901 San Antonio Road, Palo Alto, California, 94303, U.S.A.
 * All rights reserved.
 *
 * This software is the confidential and proprietary information
 * of Sun Microsystems, Inc. ("Confidential Information").  You
 * shall not disclose such Confidential Information and shall use
 * it only in accordance with the terms of the license agreement
 * you entered into with Sun.
 */

package java.lang;

/**
 * A string buffer implements a mutable sequence of characters.
 * <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.
 * <p>
 * String buffers are used by the compiler to implement the binary
 * string concatenation operator <code>+</code>. For example, the code:
 * <p><blockquote><pre>
 *     x = "a" + 4 + "c"
 * </pre></blockquote><p>
 * is compiled to the equivalent of:
 * <p><blockquote><pre>
 *     x = new StringBuffer().append("a").append(4).append("c")
 *                           .toString()
 * </pre></blockquote><p>
 * The principal operations on a <code>StringBuffer</code> are the
 * <code>append</code> and <code>insert</code> 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</code> method always adds these characters at the end
 * of the buffer; the <code>insert</code> method adds the characters at
 * a specified point.
 * <p>
 * For example, if <code>z</code> refers to a string buffer object
 * whose current contents are "<code>start</code>", then
 * the method call <code>z.append("le")</code> would cause the string
 * buffer to contain "<code>startle</code>", whereas
 * <code>z.insert(4, "le")</code> would alter the string buffer to
 * contain "<code>starlet</code>".
 * <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.
 *
 * @author	Arthur van Hoff
 * @version 	1.36, 10/28/98
 * @see     java.io.ByteArrayOutputStream
 * @see     java.lang.String
 * @since   JDK1.0
 */

public final class StringBuffer implements java.io.Serializable {
    /** The value is used for character storage. */
    private char value[];

    /** The count is the number of characters in the buffer. */
    private int count;

    /** A flag indicating whether the buffer is shared */
    private boolean shared;

    /** 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.
     *
     * @since   JDK1.0
     */
    public StringBuffer() {
	this(16);
    }

    /**
     * Constructs a string buffer with no characters in it and an
     * initial capacity specified by the <code>length</code> argument.
     *
     * @param      length   the initial capacity.
     * @exception  NegativeArraySizeException  if the <code>length</code>
     *               argument is less than <code>0</code>.
     * @since      JDK1.0
     */
    public StringBuffer(int length) {
	value = new char[length];
	shared = false;
    }

    /**
     * Constructs a string buffer so that it represents the same
     * sequence of characters as the string argument. The initial
     * capacity of the string buffer is <code>16</code> plus the length
     * of the string argument.
     *
     * @param   str   the initial contents of the buffer.
     * @since   JDK1.0
     */
    public StringBuffer(String str) {
	this(str.length() + 16);
	append(str);
    }

    /**
     * Returns the length (character count) of this string buffer.
     *
     * @return  the number of characters in this string buffer.
     * @since   JDK1.0
     */
    public int length() {
	return count;
    }

    /**
     * Returns the current capacity of the String buffer. The capacity
     * is the amount of storage available for newly inserted
     * characters; beyond which an allocation will occur.
     *
     * @return  the current capacity of this string buffer.
     * @since   JDK1.0
     */
    public int capacity() {
	return value.length;
    }

    /**
     * Copies the buffer value.  This is normally only called when shared
     * is true.  It should only be called from a synchronized method.
     */
    private final void copy() {
	char newValue[] = new char[value.length];
	System.arraycopy(value, 0, newValue, 0, count);
	value = newValue;
	shared = false;
    }

    /**
     * Ensures that the capacity of the buffer is at least equal to the
     * specified minimum.
     * If the current capacity of this string buffer is less than the
     * argument, then a new internal buffer is allocated with greater
     * capacity. The new capacity is the larger of:
     * <ul>
     * <li>The <code>minimumCapacity</code> argument.
     * <li>Twice the old capacity, plus <code>2</code>.
     * </ul>
     * If the <code>minimumCapacity</code> argument is nonpositive, this
     * method takes no action and simply returns.
     *
     * @param   minimumCapacity   the minimum desired capacity.
     * @since   JDK1.0
     */
    public synchronized void ensureCapacity(int minimumCapacity) {
	if (minimumCapacity > value.length) {
	    expandCapacity(minimumCapacity);
	}
    }

    /**
     * This implements the expansion semantics of ensureCapacity but is
     * unsynchronized for use internally by methods which are already
     * synchronized.
     *
     * @see java.lang.StringBuffer#ensureCapacity(int)
     */
    private void expandCapacity(int minimumCapacity) {
	int newCapacity = (value.length + 1) * 2;
	if (minimumCapacity > newCapacity) {
	    newCapacity = minimumCapacity;
	}

	char newValue[] = new char[newCapacity];
	System.arraycopy(value, 0, newValue, 0, count);
	value = newValue;
	shared = false;
    }

    /**
     * Sets the length of this String buffer.
     * If the <code>newLength</code> argument is less than the current
     * length of the string buffer, the string buffer is truncated to
     * contain exactly the number of characters given by the
     * <code>newLength</code> argument.
     * <p>
     * If the <code>newLength</code> argument is greater than or equal
     * to the current length, sufficient null characters
     * (<code>'&#92;u0000'</code>) are appended to the string buffer so that
     * length becomes the <code>newLength</code> argument.
     * <p>
     * The <code>newLength</code> argument must be greater than or equal
     * to <code>0</code>.
     *
     * @param      newLength   the new length of the buffer.
     * @exception  StringIndexOutOfBoundsException  if the
     *               <code>newLength</code> argument is invalid.
     * @see        java.lang.StringBuffer#length()
     * @since      JDK1.0
     */
    public synchronized void setLength(int newLength) {
	if (newLength < 0) {
	    throw new StringIndexOutOfBoundsException(newLength);
	}

	if (newLength > value.length) {
	    expandCapacity(newLength);
	}

	if (count < newLength) {
	    if (shared) copy();
	    for (; count < newLength; count++) {
		value[count] = '\0';
	    }
	} else {
            count = newLength;
            if (shared) copy();
        }
    }

    /**
     * Returns the character at a specific index in this string buffer.
     * <p>
     * The first character of a string buffer is at index
     * <code>0</code>, the next at index <code>1</code>, and so on, for
     * array indexing.
     * <p>
     * The index argument must be greater than or equal to
     * <code>0</code>, and less than the length of this string buffer.
     *
     * @param      index   the index of the desired character.
     * @return     the character at the specified index of this string buffer.
     * @exception  StringIndexOutOfBoundsException  if the index is invalid.
     * @see        java.lang.StringBuffer#length()
     * @since      JDK1.0
     */
    public synchronized char charAt(int index) {
	if ((index < 0) || (index >= count)) {
	    throw new StringIndexOutOfBoundsException(index);
	}
	return value[index];
    }

    /**
     * Characters are copied from this string buffer into the
     * destination character array <code>dst</code>. The first character to
     * be copied is at index <code>srcBegin</code>; the last character to
     * be copied is at index <code>srcEnd-1.</code> The total number of
     * characters to be copied is <code>srcEnd-srcBegin</code>. The
     * characters are copied into the subarray of <code>dst</code> starting
     * at index <code>dstBegin</code> and ending at index:
     * <p><blockquote><pre>
     *     dstbegin + (srcEnd-srcBegin) - 1
     * </pre></blockquote>
     *
     * @param      srcBegin   start copying at this offset in the string buffer.
     * @param      srcEnd     stop copying at this offset in the string buffer.
     * @param      dst        the array to copy the data into.
     * @param      dstBegin   offset into <code>dst</code>.
     * @exception  StringIndexOutOfBoundsException  if there is an invalid
     *               index into the buffer.
     * @since      JDK1.0
     */
    public synchronized void getChars(int srcBegin, int srcEnd, char dst[], int dstBegin) {
	if ((srcBegin < 0) || (srcBegin >= count)) {
	    throw new StringIndexOutOfBoundsException(srcBegin);
	}
	if ((srcEnd < 0) || (srcEnd > count)) {
	    throw new StringIndexOutOfBoundsException(srcEnd);
	}
	if (srcBegin < srcEnd) {
	    System.arraycopy(value, srcBegin, dst, dstBegin, srcEnd - srcBegin);
	}
    }

    /**
     * The character at the specified index of this string buffer is set
     * to <code>ch</code>.
     * <p>
     * The offset argument must be greater than or equal to
     * <code>0</code>, and less than the length of this string buffer.
     *
     * @param      index   the index of the character to modify.
     * @param      ch      the new character.
     * @exception  StringIndexOutOfBoundsException  if the index is invalid.
     * @see        java.lang.StringBuffer#length()
     * @since      JDK1.0
     */
    public synchronized void setCharAt(int index, char ch) {
	if ((index < 0) || (index >= count)) {
	    throw new StringIndexOutOfBoundsException(index);
	}
	if (shared) copy();
	value[index] = ch;
    }

    /**
     * Appends the string representation of the <code>Object</code>
     * argument to this string buffer.
     * <p>
     * The argument is converted to a string as if by the method
     * <code>String.valueOf</code>, and the characters of that
     * string are then appended to this string buffer.
     *
     * @param   obj   an <code>Object</code>.
     * @return  this string buffer.
     * @see     java.lang.String#valueOf(java.lang.Object)
     * @see     java.lang.StringBuffer#append(java.lang.String)
     * @since   JDK1.0
     */
    public synchronized StringBuffer append(Object obj) {
	return append(String.valueOf(obj));
    }

    /**
     * Appends the string to this string buffer.
     * <p>
     * The characters of the <code>String</code> argument are appended, in
     * order, to the contents of this string buffer, increasing the
     * length of this string buffer by the length of the argument.
     *
     * @param   str   a string.
     * @return  this string buffer.
     * @since   JDK1.0
     */
    public synchronized StringBuffer append(String str) {
	if (str == null) {
	    str = String.valueOf(str);
	}

	int len = str.length();
	int newcount = count + len;
	if (newcount > value.length)
	    expandCapacity(newcount);
	str.getChars(0, len, value, count);
	count = newcount;
	return this;
    }

    /**
     * Appends the string representation of the <code>char</code> array
     * argument to this string buffer.
     * <p>
     * The characters of the array argument are appended, in order, to
     * the contents of this string buffer. The length of this string
     * buffer increases by the length of the argument.
     *
     * @param   str   the characters to be appended.
     * @return  this string buffer.
     * @since   JDK1.0
     */
    public synchronized StringBuffer append(char str[]) {
	int len = str.length;
	int newcount = count + len;
	if (newcount > value.length)
	    expandCapacity(newcount);
	System.arraycopy(str, 0, value, count, len);
	count = newcount;
	return this;
    }

    /**
     * Appends the string representation of a subarray of the
     * <code>char</code> array argument to this string buffer.
     * <p>
     * Characters of the character array <code>str</code>, starting at
     * index <code>offset</code>, are appended, in order, to the contents
     * of this string buffer. The length of this string buffer increases
     * by the value of <code>len</code>.
     *
     * @param   str      the characters to be appended.
     * @param   offset   the index of the first character to append.
     * @param   len      the number of characters to append.
     * @return  this string buffer.
     * @since   JDK1.0
     */
    public synchronized StringBuffer append(char str[], int offset, int len) {
        int newcount = count + len;
	if (newcount > value.length)
	    expandCapacity(newcount);
	System.arraycopy(str, offset, value, count, len);
	count = newcount;
	return this;
    }

    /**
     * Appends the string representation of the <code>boolean</code>
     * argument to the string buffer.
     * <p>
     * The argument is converted to a string as if by the method
     * <code>String.valueOf</code>, and the characters of that
     * string are then appended to this string buffer.
     *
     * @param   b   a <code>boolean</code>.
     * @return  this string buffer.