string.java

已经移植好的java虚拟机

/*
 * Copyright 1994-2002 Sun Microsystems, Inc. All Rights Reserved.
 *
 * This software is the proprietary information of Sun Microsystems, Inc.
 * Use is subject to license terms.
 *
 */

package java.lang;

import java.io.UnsupportedEncodingException;
import com.sun.cldc.i18n.*;

/**
 * The <code>String</code> class represents character strings. All
 * string literals in Java programs, such as <code>"abc"</code>, are
 * implemented as instances of this class.
 * <p>
 * Strings are constant; their values cannot be changed after they
 * are created. String buffers support mutable strings.
 * Because String objects are immutable they can be shared. For example:
 * <p><blockquote><pre>
 *     String str = "abc";
 * </pre></blockquote><p>
 * is equivalent to:
 * <p><blockquote><pre>
 *     char data[] = {'a', 'b', 'c'};
 *     String str = new String(data);
 * </pre></blockquote><p>
 * Here are some more examples of how strings can be used:
 * <p><blockquote><pre>
 *     System.out.println("abc");
 *     String cde = "cde";
 *     System.out.println("abc" + cde);
 *     String c = "abc".substring(2,3);
 *     String d = cde.substring(1, 2);
 * </pre></blockquote>
 * <p>
 * The class <code>String</code> includes methods for examining
 * individual characters of the sequence, for comparing strings, for
 * searching strings, for extracting substrings, and for creating a
 * copy of a string with all characters translated to uppercase or to
 * lowercase.
 * <p>
 * The Java language provides special support for the string
 * concatenation operator (&nbsp;+&nbsp;), and for conversion of
 * other objects to strings. String concatenation is implemented
 * through the <code>StringBuffer</code> class and its
 * <code>append</code> method.
 * String conversions are implemented through the method
 * <code>toString</code>, defined by <code>Object</code> and
 * inherited by all classes in Java. For additional information on
 * string concatenation and conversion, see Gosling, Joy, and Steele,
 * <i>The Java Language Specification</i>.
 *
 * @author  Lee Boynton
 * @author  Arthur van Hoff
 * @version 1.121, 10/06/99 (CLDC 1.0, Spring 2000)
 * @see     java.lang.Object#toString()
 * @see     java.lang.StringBuffer
 * @see     java.lang.StringBuffer#append(boolean)
 * @see     java.lang.StringBuffer#append(char)
 * @see     java.lang.StringBuffer#append(char[])
 * @see     java.lang.StringBuffer#append(char[], int, int)
 * @see     java.lang.StringBuffer#append(int)
 * @see     java.lang.StringBuffer#append(long)
 * @see     java.lang.StringBuffer#append(java.lang.Object)
 * @see     java.lang.StringBuffer#append(java.lang.String)
 * @since   JDK1.0, CLDC 1.0
 */
public final
class String {

    /** The value is used for character storage. */
    private char value[];

    /** The offset is the first index of the storage that is used. */
    private int offset;

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

    /**
     * Initializes a newly created <code>String</code> object so that it
     * represents an empty character sequence.
     */
    public String() {
        value = new char[0];
    }

    /**
     * Initializes a newly created <code>String</code> object so that it
     * represents the same sequence of characters as the argument; in other
     * words, the newly created string is a copy of the argument string.
     *
     * @param   value   a <code>String</code>.
     */
    public String(String value) {
        count = value.length();
        this.value = new char[count];
        value.getChars(0, count, this.value, 0);
    }

    /**
     * Allocates a new <code>String</code> so that it represents the
     * sequence of characters currently contained in the character array
     * argument. The contents of the character array are copied; subsequent
     * modification of the character array does not affect the newly created
     * string.
     *
     * @param  value   the initial value of the string.
     * @throws NullPointerException if <code>value</code> is <code>null</code>.
     */
    public String(char value[]) {
        this.count = value.length;
        this.value = new char[count];
        System.arraycopy(value, 0, this.value, 0, count);
    }

    /**
     * Allocates a new <code>String</code> that contains characters from
     * a subarray of the character array argument. The <code>offset</code>
     * argument is the index of the first character of the subarray and
     * the <code>count</code> argument specifies the length of the
     * subarray. The contents of the subarray are copied; subsequent
     * modification of the character array does not affect the newly
     * created string.
     *
     * @param      value    array that is the source of characters.
     * @param      offset   the initial offset.
     * @param      count    the length.
     * @exception  IndexOutOfBoundsException  if the <code>offset</code>
     *               and <code>count</code> arguments index characters outside
     *               the bounds of the <code>value</code> array.
     * @exception NullPointerException if <code>value</code> is
     *               <code>null</code>.
     */
    public String(char value[], int offset, int count) {
        if (offset < 0) {
            throw new StringIndexOutOfBoundsException(offset);
        }
        if (count < 0) {
            throw new StringIndexOutOfBoundsException(count);
        }
        // Note: offset or count might be near -1>>>1.
        if (offset > value.length - count) {
            throw new StringIndexOutOfBoundsException(offset + count);
        }

        this.value = new char[count];
        this.count = count;
        System.arraycopy(value, offset, this.value, 0, count);
    }

    /**
     * Construct a new <code>String</code> by converting the specified
     * subarray of bytes using the specified character encoding.  The length of
     * the new <code>String</code> is a function of the encoding, and hence may
     * not be equal to the length of the subarray.
     *
     * @param  bytes   The bytes to be converted into characters
     * @param  off     Index of the first byte to convert
     * @param  len     Number of bytes to convert
     * @param  enc     The name of a character encoding
     *
     * @exception  UnsupportedEncodingException
     *             If the named encoding is not supported
     * @since      JDK1.1
     */
    public String(byte bytes[], int off, int len, String enc)
        throws UnsupportedEncodingException
    {
        this(Helper.byteToCharArray(bytes, off, len, enc));
    }

    /**
     * Construct a new <code>String</code> by converting the specified array
     * of bytes using the specified character encoding.  The length of the new
     * <code>String</code> is a function of the encoding, and hence may not be
     * equal to the length of the byte array.
     *
     * @param  bytes   The bytes to be converted into characters
     * @param  enc     The name of a supported character encoding
     *
     * @exception  UnsupportedEncodingException
     *             If the named encoding is not supported
     * @since      JDK1.1
     */
    public String(byte bytes[], String enc)
        throws UnsupportedEncodingException
    {
        this(bytes, 0, bytes.length, enc);
    }

    /**
     * Construct a new <code>String</code> by converting the specified
     * subarray of bytes using the platform's default character encoding.  The
     * length of the new <code>String</code> is a function of the encoding, and
     * hence may not be equal to the length of the subarray.
     *
     * @param  bytes   The bytes to be converted into characters
     * @param  off     Index of the first byte to convert
     * @param  len     Number of bytes to convert
     * @since  JDK1.1
     */
    public String(byte bytes[], int off, int len) {
        this(Helper.byteToCharArray(bytes, off, len));
    }

    /**
     * Construct a new <code>String</code> by converting the specified array
     * of bytes using the platform's default character encoding.  The length of
     * the new <code>String</code> is a function of the encoding, and hence may
     * not be equal to the length of the byte array.
     *
     * @param  bytes   The bytes to be converted into characters
     * @since  JDK1.1
     */
    public String(byte bytes[]) {
        this(bytes, 0, bytes.length);
    }

    /**
     * Allocates a new string that contains the sequence of characters
     * currently contained in the string buffer argument. The contents of
     * the string buffer are copied; subsequent modification of the string
     * buffer does not affect the newly created string.
     *
     * @param   buffer   a <code>StringBuffer</code>.
     * @throws NullPointerException If <code>buffer</code> is
     * <code>null</code>.
     */
    public String (StringBuffer buffer) {
        synchronized(buffer) {
            buffer.setShared();
            this.value = buffer.getValue();
            this.offset = 0;
            this.count = buffer.length();
        }
    }

    // Package private constructor which shares value array for speed.
    String(int offset, int count, char value[]) {
        this.value = value;
        this.offset = offset;
        this.count = count;
    }

    /**
     * Returns the length of this string.
     * The length is equal to the number of 16-bit
     * Unicode characters in the string.
     *
     * @return  the length of the sequence of characters represented by this
     *          object.
     */
    public int length() {
        return count;
    }

    /**
     * Returns the character at the specified index. An index ranges
     * from <code>0</code> to <code>length() - 1</code>. The first character
     * of the sequence is at index <code>0</code>, the next at index
     * <code>1</code>, and so on, as for array indexing.
     *
     * @param      index   the index of the character.
     * @return     the character at the specified index of this string.
     *             The first character is at index <code>0</code>.
     * @exception  IndexOutOfBoundsException  if the <code>index</code>
     *             argument is negative or not less than the length of this
     *             string.
     */
    public native char charAt(int index);
 /******
  * public char charAt(int index) {
  *     if ((index < 0) || (index >= count)) {
  *         throw new StringIndexOutOfBoundsException(index);
  *     }
  *     return value[index + offset];
  * }
  *****/

    /**
     * Copies characters from this string into the destination character
     * array.
     * <p>
     * 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>
     * (thus 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   index of the first character in the string
     *                        to copy.
     * @param      srcEnd     index after the last character in the string
     *                        to copy.
     * @param      dst        the destination array.
     * @param      dstBegin   the start offset in the destination array.
     * @exception IndexOutOfBoundsException If any of the following
     *            is true:
     *            <ul><li><code>srcBegin</code> is negative.
     *            <li><code>srcBegin</code> is greater than <code>srcEnd</code>
     *            <li><code>srcEnd</code> is greater than the length of this
     *                string
     *            <li><code>dstBegin</code> is negative
     *            <li><code>dstBegin+(srcEnd-srcBegin)</code> is larger than
     *                <code>dst.length</code></ul>
     * @exception NullPointerException if <code>dst</code> is <code>null</code>
     */
    public void getChars(int srcBegin, int srcEnd, char dst[], int dstBegin) {
        if (srcBegin < 0) {
            throw new StringIndexOutOfBoundsException(srcBegin);