StringBuffer类详解

StringBuffer类详解

package com.zp.demo2;public class Test1 {public static void main(String[] args) {// TODO Auto-generated method stub   StringBuffer sb1 = new StringBuffer();//构造一个其中不带字符的字符串缓冲区(底层是数组存储)，初始容量为 16 个字符          StringBuffer sb2 = new StringBuffer("abc"); /*构造一个初始化为内容的字符串缓冲区指定字符串。 字符串缓冲区的初始容量是16加上字符串参数的长度。*/     StringBuffer sb3 = new StringBuffer('a');//当为字符时相当于数字 /*构造一个没有字符的字符串缓冲区.指定的初始容量。*/   StringBuffer sb4 = new StringBuffer(13);//13指定初始缓冲区大小 /*构造一个没有字符的字符串缓冲区.指定的初始容量。*/  }}

StringBuffer类构造方法：

  /**     * Constructs a string buffer with no characters in it and an     * initial capacity of 16 characters.     */    public StringBuffer() {        super(16);    }

    /**     * Constructs a string buffer initialized to the contents of the     * specified string. 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.     * @exception NullPointerException if <code>str</code> is <code>null</code>     */    public StringBuffer(String str) {        super(str.length() + 16);        append(str);    }

    /**     * Constructs a string buffer with no characters in it and     * the specified initial capacity.     *     * @param      capacity  the initial capacity.     * @exception  NegativeArraySizeException  if the <code>capacity</code>     *               argument is less than <code>0</code>.     */    public StringBuffer(int capacity) {        super(capacity);    }

    /**     * Constructs a string buffer that contains the same characters     * as the specified <code>CharSequence</code>. The initial capacity of     * the string buffer is <code>16</code> plus the length of the     * <code>CharSequence</code> argument.     * <p>     * If the length of the specified <code>CharSequence</code> is     * less than or equal to zero, then an empty buffer of capacity     * <code>16</code> is returned.     *     * @param      seq   the sequence to copy.     * @exception NullPointerException if <code>seq</code> is <code>null</code>     * @since 1.5     */    public StringBuffer(CharSequence seq) {        this(seq.length() + 16);        append(seq);    }

         

        以上为StringBuffer类的四个构造方法。当不带参数时，构造一个其中不带字符的字符串缓冲区(底层是数组存储)，初始容量为 16 个字符。当参数为String类型为，字符串缓冲区的初始容量是16加上字符串参数的长度。当参数类型为整型时， 字符串缓冲区的初始容量是16加上字符串参数的长度。