Set集合-HashSet

HsahSet---无序，不可重复

package eight.set.hashset;

import java.util.HashSet;
import java.util.Iterator;

public class Demo01 {
    public static void main(String[] args) {
        //为什么之前重复的字符串没有存进HashSet集合中？
        //String类本身已经重写HashCode()方法和equals()
        HashSet<String> hs = new HashSet<String>();
        hs.add("车次：G4172");
        hs.add("出发站：青岛");
        hs.add("到达站：北京南");
        hs.add("历时时间：4:53");
        hs.add("车票：6车厢3FB");
        hs.add("车票：6车厢3FB");//不能重复
        //HashSet没有下标不能用for循环
        //foreach
        for (String string:hs){
            System.out.println(string);
        }
        //迭代器
        Iterator<String> it = hs.iterator();
        while(it.hasNext()){
            System.out.println(it.next());
        }
    }
}

package eight.set.hashset;

import java.util.Objects;

public class Student {
    private String name;
    private int age;

    public Student() {
    }

    public Student(String name, int age) {
        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 "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
    //重写equals() 用于在两个元素位置相同的时候比较两个元素是否相等
    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Student student = (Student) o;
        return age == student.age && Objects.equals(name, student.name);
    }

    //重写hashCode() 用于获得元素的存储位置
    @Override
    public int hashCode() {
        return Objects.hash(name, age);
    }
}

package eight.set.hashset;

import java.util.HashMap;
import java.util.HashSet;

public class Test {
    public static void main(String[] args) {
        //Student类重写HashCode方法和equals方法后不能重复存储
        Student s1 = new Student("龙龙",25);//先计算哈希码值，如哈希码值相等则调用equals方法看属性是否相等
        Student s2 = new Student("壮壮",22);
        Student s3 = new Student("成成",27);
        Student s4 = new Student("成成",27);
        HashSet<Student> hs = new HashSet<>();
        hs.add(s1);
        hs.add(s2);
        hs.add(s3);
        hs.add(s4);
        for (Student student:hs){
            System.out.println(student);
        }

    }
}