set 接口（ HashSet）

 基础

import java.util.HashSet;

public class Demo02 {
    public static void main(String[] args) {
        //set接口
        HashSet<String> set=new HashSet<String>();
        set.add("abc");
        set.add("abc");
        set.add("bcd");
        //遍历
        for (String string : set) {
            System.out.println(string);
        }
        
        
        System.out.println("adc".hashCode());//hashCode算法
        
        
    }
}

 自定义对象

//自定义类
package com.oracle.demo01;

public class Person {
    private String name;
    private int age;
    
    
    public String toString() {
        return "Person [name=" + name + ", age=" + age + "]";
    }
    
    // 重写   hashCode() 方法
    /*public int hashCode() {
        
        return name.hashCode()+age*31;//这是重点
    }*/
    
    // 重写  equals 方法
    /*public boolean equals(Object obj) {
        if(obj==this){
            return true;
        }
        if(obj==null){
            return false;
        }
        if(obj instanceof Person){
            Person p=(Person)obj;
            return p.name.equals(this.name)&&p.age==this.age;
        }
        return false;
    }*/
    
    @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;
    }

    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;
    }
}

 

//测试类
package com.oracle.demo01;

import java.util.HashSet;

public class Demo03 {
    public static void main(String[] args) {
        //自定义类，别忘了重写hashCode()方法和equals()方法
        HashSet<Person> set=new HashSet<Person>();
        set.add(new Person("a",18));
        set.add(new Person("b",17));
        set.add(new Person("a",18));
        for (Person person : set) {
            System.out.println(person);
            System.out.println(person.hashCode());
        }
    }
}

 

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