[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);      }  }