JAVA BASE

Set(不能加入重复的元素) 中的HashSet(散列存放)和TreeSet(有序存放)

1.TreeSet 排序原理

Exception in thread "main" java.lang.ClassCastException: test.Person cannot be cast to java.lang.Comparable (问题的解决!)

 

import java.util.Set;
import java.util.TreeSet;
class Person implements Comparable<Person>{
    private String name;
    private int age;
    public Person(String name,int age){
        this.name = name;
        this.age = age;
    }
    public String toString(){
        return "姓名:" + this.name + "，年龄:" + this.age;
    }
    public int compareTo(Person per) {
        if(this.age>per.age){
            return 1;
        }else if(this.age<per.age){
            return 2;
        }else{
            return this.name.compareTo(per.name);
        }
    }
}
public class TreeSetDemo {
    public static void main(String[] args) {
        Set<Person> allSet = new TreeSet<Person>();
        allSet.add(new Person("张三",30));
        allSet.add(new Person("李四",31));
        allSet.add(new Person("王五",32));
        allSet.add(new Person("赵六1",33));
        allSet.add(new Person("孙七2",33));
        System.out.println(allSet);
    }
}

 

2.Set 接口中重复元素的定义

import java.util.Set;
import java.util.HashSet;
class Person{
    private String name;
    private int age;
    public Person(String name,int age){
        this.name = name;
        this.age = age;
    }
    public String toString(){
        return "姓名:" + this.name + "，年龄:" + this.age;
    }
    public boolean equals(Object obj){
        if(this == obj){
            return true;
        }
        if(!(obj instanceof Person)){
            return false;
        }
        Person per = (Person)obj;
        if(this.name.equals(per.name)&&this.age==per.age){
            return true;
        }else{
            return false;
        }
    }
    public int hashCode(){
        return this.name.hashCode()*this.age;
    }
}
public class HashSetDemo {
    public static void main(String[] args) {
        Set<Person> allSet = null;
        allSet = new HashSet<Person>();
        allSet.add(new Person("张三",30));
        allSet.add(new Person("李四",31));
        allSet.add(new Person("王五",32));
        allSet.add(new Person("赵六2",33));
        allSet.add(new Person("赵六2",33));
        allSet.add(new Person("孙七",33));
        System.out.println(allSet);
    }
}