[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);
}
}