[Java Core]Java类的equals方法的实现

Java对equals方法的要求：

1. 自反性：x.equals(x) == true

2. 对称性：x.equals(y) == y.equals(x)

3. 传递性：

x.equals(y) == true && y.equals(z) == true   =>    x.equals(z) == true

4. 一致性：若x,y均没有发生变化，x.equals(y)的结果不论调用多少次，都不发生变化

5. 非空结果：x.equals(null) == false

依据这几点要求，书中给出了一个完善的比较类的方法：

import java.util.Objects;  
  
public class Employee {  
    public String member;  
    public Object obj;  
    public Employee(final String Member, final Object Obj){  
        member = Member;  
        obj = Obj;  
    }  
    public boolean equals(Object otherObj){  
          
        //refer to same object, return true  
        if(this == otherObj) return true;  
          
        //otherObj is null, return false  
        if(otherObj == null) return false;  
          
        //belong to different class, return false  
        if(this.getClass() != otherObj.getClass()) return false;  
          
        //solve the problem of comparison between super obj and child obj  
        if(!(otherObj instanceof Employee)) return false;  
          
        Employee other = (Employee)otherObj;  
          
        //in case obj or other.obj is null  
        return Objects.equals(obj, other.obj)  
            && member.equals(other.member);  
    }  
}