equals ==相比较

看到一段代码，对equals 和==还是有点不解，于是重新实践了一翻来验证结果，代码如下：

package test;public class test {public static void main(String[] args) {EqualsMethod equals=new EqualsMethod();equals.Equals1();equals.Equals2();equals.Equals3();equals.Equals4();}}class Value{public Value(String i){this.i=i;}public Value(){}String i;}class Value2{public Value2(String i){this.i=i;}public Value2(){}String i;public String getI() {return i;}public void setI(String i) {this.i = i;}@Overridepublic boolean equals(Object obj) {//Value2 v=(Value2)obj;//System.out.println("hashcode:"+super.hashCode());//System.out.println(this.toString());return super.equals(obj)|| i == ((Value2) obj).getI();}@Overridepublic String toString() {return "Value2 [i=" + i + "]";}}//==比较的两个对象的引用，equals 是内容/*

*注意：Object 类中定义的 equals(Object) 方法是直接使用 “==” 比较的两个对象，

*所以在没有覆盖 (override，或称改写、重写) equals(Object) 方法的情况下，equals(Object) 与 “==” 一样是比较的引用

*/class EqualsMethod{public void  Equals1(){Value v1=new Value();Value v2=new Value();v1.i=v2.i="abc";System.out.println("Equals1:v1==v2:"+(v1==v2));System.out.println("Equals1:v1 equals v2:"+v1.equals(v2));}public void  Equals2(){Value v1=new Value("a");Value v2=new Value("a");String s1=new String("a");        String s2=new String("a");        Value2 v3=new Value2("a");Value2 v4=new Value2("a");System.out.println("Equals2:v1==v2:"+(v1==v2));System.out.println("Equals2:v1 equals v2:"+v1.equals(v2));//false//没有重写equals方法  相当于还是直接比较的引用System.out.println("Equals2:v1==v2:"+(s1==s2));System.out.println("Equals2:v1 equals v2:"+s1.equals(s2));//true//因为String 默认重写了equals方法System.out.println("Equals2:v4==v3:"+(v3==v4));System.out.println("Equals2:v3 equals v4:"+v3.equals(v4));//true//需手动重写equals方法}public void  Equals3(){Integer n1 = new Integer(47);    Integer n2 = new Integer(47);    System.out.println("Equals3:"+n1.equals(n2));//true}public void  Equals4(){String s1=new String("a");        String s2=new String("a");                System.out.println("Equals4:s1==s2:"+(s1==s2)); //false        System.out.println("Equals4:s1==s2:"+(s1.equals(s2)));        s1=s2;        System.out.println("Equals4:用 == 比较结果"+(s1==s2)); //true}}

测试结果：

Equals1:v1==v2:false
Equals1:v1 equals v2:false
Equals2:v1==v2:false
Equals2:v1 equals v2:false
Equals2:v1==v2:false
Equals2:v1 equals v2:true
Equals2:v4==v3:false
Equals2:v3 equals v4:true
Equals3:true
Equals4:s1==s2:false
Equals4:s1==s2:true
Equals4:用 == 比较结果true