StringBuffer总结分析

构造方法

/**
     * Constructs a string buffer with no characters in it and an
     * initial capacity of 16 characters.
     *    创建容量为16个char大小的空间
     */
    public StringBuffer() {
        super(16);
    }
 
     /**
     * Constructs a string buffer with no characters in it and
     * the specified initial capacity.
     *创建一个指定容量的StringBuffer对象
     * @param      capacity  the initial capacity.
     * @exception  NegativeArraySizeException  if the {@code capacity}
     *               argument is less than {@code 0}.
     */
    public StringBuffer(int capacity) {
        super(capacity);
    }
 
     /**
     *初始化一个有指定string的对象，空间大小为string.length+16
     * 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.
     */
    public StringBuffer(String str) {
        super(str.length() + 16);  //new char[str.length() + 16]
        append(str);
    }

append方法 如果string的长度大于capacity的增String会自动增加容量

以下情况，容器容量需要扩展

2.当capacity<str<2*capacity+2时，值为 2*capacity+2

3.当string>2*capacity+2时，值为string