//Person类public class Person { private String name;
private int age; public Person() {
super();
} public Person(String name, int age) {
super();
this.name = name;
this.age = age;
} public String getName() {
return name;
} public void setName(String name) {
this.name = name;
} public int getAge() {
return age;
} public void setAge(int age) {
this.age = age;
} @Override
public String toString() {
return name + "===========" + age;
} @Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + age;
result = prime * result + ((name == null) ? 0 : name.hashCode());
return result;
} @Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
Person other = (Person) obj;
if (age != other.age)
return false;
if (name == null) {
if (other.name != null)
return false;
} else if (!name.equals(other.name))
return false;
return true;
}}
//Test(主类)import java.util.HashSet;
import java.util.Set;public class Test {
public static void main(String[] args) {
Set<Person> set = new HashSet<Person>();
set.add(new Person("李四",3));
set.add(new Person("张三",2));
set.add(new Person("张三",2));
set.add(new Person("王五",4));
System.out.println(set.toString());
}
}
为什么Set去重复的时候,必须重写equals和hashCode方法,只重写equals把比较地址改变为比较内容不就够了吗?
就算要重写equals,重写的里面是什么意思呢?
equals(obj) {
return this.age == obj.age;
}
也就是只要年龄相等就视同这两个对象相等。
final int prime = 31;
int result = 1;
result = prime * result + age; //result先是age+31的值。
result = prime * result + ((name == null) ? 0 : name.hashCode());//之后又被0或者name.hashCode覆盖。
return result; //最后返回的是一个name的hashCode值,这,有什么意义呢?
}
public int hashCode() {
return name.hashCode() + age;
}
public boolean equals(Object obj) {
Person tmp = (Person) obj;
return this.age == tmp.age && this.name.equals(tmp.name);
}