/**
	 *  基本的数据结构
	 */
	
    /** The value is used for character storage. */
    private final char value[];

    /** Cache the hash code for the string */
    private int hash; // Default to 0

public String(String original) {
    this.value = original.value;
    this.hash = original.hash;
} ## equals

 public boolean equals(Object anObject) {
       //地址都一样，不用说了
        if (this == anObject) {
            return true;
        }
        //类型判断
        if (anObject instanceof String) {
            String anotherString = (String)anObject;
            int n = value.length;
            //长度判断
            if (n == anotherString.value.length) {
                char v1[] = value;
                char v2[] = anotherString.value;
                int i = 0;
                //循环判断字符数组元素是否一样
                while (n-- != 0) {
                    if (v1[i] != v2[i])
                        return false;
                    i++;
                }
                return true;
            }
        }
        return false;
    }

public String substring(int beginIndex) {
    if (beginIndex < 0) {
        throw new StringIndexOutOfBoundsException(beginIndex);
    }
    int subLen = value.length - beginIndex;
    if (subLen < 0) {
        throw new StringIndexOutOfBoundsException(subLen);
    }
    return (beginIndex == 0) ? this : new String(value, beginIndex, subLen);
}

//先判断是否越界
    public char charAt(int index) {
        if ((index < 0) || (index >= value.length)) {
            throw new StringIndexOutOfBoundsException(index);
        }
        return value[index];
    }

public int length() {
    return value.length;
}