1. compareTo 返回第一位不相等字元值之差,然後返回兩字串長度之差。

public int compareTo(String anotherString) {
        int len1 = value.length;
        int len2 = anotherString.value.length;
        int lim = Math.min(len1, len2);
        char v1[] = value;
        char v2[] = anotherString.value;

        int k = 0;
        while (k < lim) {
            char c1 = v1[k];
            char c2 = v2[k];
            if (c1 != c2) {
                return c1 - c2;
            }
            k++;
        }
        return len1 - len2;
    }
 

        public String a = "123";
	public String b = "123";
	public String c = "1234";
	public String d = "126";
	
	
	@Test
	public void compareTo(){
		System.out.println(a.compareTo(b));//0--相同
		System.out.println(a.compareTo(d));//-3--不相同的char值差
		System.out.println(a.compareTo(c));//-1--長度差
	}