当新建一个java类时,需要重写equals和hashcode方法,大家都知道!但是,为什么要重写呢?
需要保证对象调用equals方法为true时,hashcode必须相同.
先看下面的例子:
没有重写equals和hashcode方法User类
public class User {
private Integer age;
private String name;
public User() {
}
public User(Integer age, String name) {
this.age = age;
this.name = name;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
@Test
public void test01(){
User user1 = new User(12, "lyf");
User user2 = new User(12, "lyf");
System.out.println("hashcode值:");
System.out.println(user1.hashCode());
System.out.println(user2.hashCode());
System.out.println("是否相等:");
System.out.println(user1.equals(user2));
}
了解hashcode算法的话你会明白,即使hashcode相同值也有可能不同!那么,就需要我们重写这两个方法.
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
User user = (User) o;
return Objects.equals(age, user.age) &&
Objects.equals(name, user.name);
}
@Override
public int hashCode() {
return Objects.hash(age, name);
}
重新调用的结果:
原文：https://www.cnblogs.com/linyufeng/p/9946581.html