243 HashSet集合存储学生对象并遍历

243 HashSet集合存储学生对象并遍历

243 HashSet集合存储学生对象并遍历

这个案例练习过多次了，用HashSet来做有什么不同？——如果学生对象的成员变量值相同，视为同一个对象

不做特殊处理前，相同姓名、年龄的学生时可以重复添加到HashSet里的

如何保证相同的元素不重复添加？——重写equals()方法和hashCode()方法即可，且使用generator工具可便捷地实现重写

（在Student类里）右键-generator-construct- equals and hashCode

--------------------------------------------------------------

package e243;

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 boolean equals(Object o) {

//        if (this == o) return true;

//        if (o == null || getclass() != o.getclass()) return false;

//

//        Student student = (Student) o;

//

//        if (age != student.age) return false;

//        return name != null ? name.equals(student.name) : student.name == null;

//    }

//

//    @Override

//    public int hashCode() {

//        int result = name != null ? name.hashCode() : 0;

//        result = 31 * result + age;

//        return result;

//    }

}

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package e243;

import java.util.HashSet;

public class HashSetDemo {

    public static void main(String[] args) {

        HashSet hs = new HashSet();

        Student s1 = new Student("TWO",22);

        Student s2 = new Student("HUNDRED",22);

        Student s3 = new Student("FORTY",22);

        Student s4 = new Student("FORTY",22);

        hs.add(s1);

        hs.add(s2);

        hs.add(s3);

        hs.add(s4);

        System.out.println("19.");

        for (Student s:hs){

            System.out.println(s.getName()+","+s.getAge());

        }

    }

}

--------------------------------------------------------------

19.

TWO,22

FORTY,22

HUNDRED,22

FORTY,22

--------------------------------------------------------------

package e243;

public class Student {

    @Override

    public boolean equals(Object o) {

        if (this == o) return true;

        if (o == null || getclass() != o.getclass()) return false;

        Student student = (Student) o;

        if (age != student.age) return false;

        return name != null ? name.equals(student.name) : student.name == null;

    }

    @Override

    public int hashCode() {

        int result = name != null ? name.hashCode() : 0;

        result = 31 * result + age;

        return result;

    }

}

--------------------------------------------------------------

19.

FORTY,22

HUNDRED,22

TWO,22