StringBuffer类和String 类的 equals 和 ==

 注意：

 equals(Object obj)equals方法的参数是任意对象
 Object类的equals方法就是用==判断的，即判断两个对象是否为同一个对象
 StringBuffer类没有重写equals方法，String类重写了equals方法，用来判断两个字符串的内容是否相同

以下为Object类的equals方法

public boolean equals(Object obj) {
    return (this == obj);

以下为String类的equals方法

 public boolean equals(Object anObject) {
        if (this == anObject) {
            return true;
        }
        if (anObject instanceof String) {
            String anotherString = (String)anObject;
            int n = value.length;
            if (n == anotherString.value.length) {
                char v1[] = value;
                char v2[] = anotherString.value;
                int i = 0;
                while (n-- != 0) {
                    if (v1[i] != v2[i])
                        return false;
                    i++;
                }
                return true;
            }
        }
        return false;
    }

public class Twine {

    public static void main(String[] args) {
        String s = "";
        StringBuffer sb1 = new StringBuffer("hi");
        StringBuffer sb2 = new StringBuffer("hi");
        StringBuffer sb3 = new StringBuffer(sb2);
        StringBuffer sb4 = sb3;
        if (sb1.equals(sb2)) {  //false
            s += "1";
        }
        if (sb2.equals(sb3)) {    //false
            s += "2";
        }
        if (sb3.equals(sb4)) {    //true
            s += "3";
        }
        if (sb1 == sb2) {        //false
            s += "ss";
        }
        
        //s2和s3指向同一个对象
        String s2 = "hi";
        String s3 = "hi";
        
        String s4 = s3;
        if (s2.equals(s3)) {    //true
            s += "4";
        }
        if (s3.equals(s4)) {    //true
            s += "5";
        }
        if (s2 == s3) {         //true
            s += "6";
        }            
        if (s3 == s4) {         //true
            s += "7";
        }
        if (sb1.equals(s2)) {   //false
            s += "8";
        }
        
        System.out.println(s);
        
//        mm和nn指向的是同一个对象
//        bb和cc指向的不是同一个对象
        
        String mm = "hi";
        String nn = "hi";
        System.out.println(mm == nn);    //true
        
        String bb = new String("hi");
        String cc = new String("hi");
        System.out.println(bb == cc);    //false
    }
}