如何将字符串反转？

在StringBuffer中实现了字符串反转的方法。

    public static String reverse(String str) {
        return str == null ? null : (new StringBuffer(str)).reverse().toString();
    }

实现

StringBuffer的父类是AbstractStringBuilder

public AbstractStringBuilder reverse() {
        boolean hasSurrogates = false;
        //数组下标最大的长度
        int n = count - 1;
        for (int j = (n-1) >> 1; j >= 0; j--) {
            // 调换字符顺序
            int k = n - j;
            char cj = value[j];
            char ck = value[k];
            value[j] = ck;
            value[k] = cj;
            //处理特殊字符的，先不用关心。
            if (Character.isSurrogate(cj) ||
                Character.isSurrogate(ck)) {
                hasSurrogates = true;
            }
        }
        if (hasSurrogates) {
            reverseAllValidSurrogatePairs();
        }
        return this;
    }

精简来看：

   /**
     * The value is used for character storage.
     * 字符存储的值
     */
    char[] value;

    /**
     * The count is the number of characters used.
     * 字符的数量 
     */
    int count;
    public AbstractStringBuilder reverse() {       
        int n = count - 1;
        for (int j = (n-1) >> 1; j >= 0; j--) {
            int k = n - j;
            char cj = value[j];
            char ck = value[k];
            value[j] = ck;
            value[k] = cj;          
        }
        return this;
    }

简单记录下