沒有toString方法：打印的是集合元素的內存地址

Student.java

package com.yikuan.test;

public class Student {
    private String name;
    private int age;
    /*構造方法*/
    public Student() {
        super();
    }
    public Student(String name, int age) {
        super();
        this.name = name;
        this.age = age;
    }
    
 
/*toSting方法*/
//    @Override
//    public String toString() {
//        return "Student [name=" + name + ", age=" + age + "]";
//    }
    /*get、set方法*/
    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;
    }
}

Test.java

package com.yikuan.test;

import java.util.ArrayList;

public class Test1 {
    public static void main(String[] args) {
        ArrayList<Student> list = new ArrayList<Student>();
        list.add(
 
new Student("aa",12));
        list.add(new Student("ww",14));
        list.add(new Student("qq",15));
        list.add(new Student("ee",51));
        for (int i = 0; i < list.size(); i++) {
            System.out.println(list.get(i));
        }
    }
}

結果：

com.yikuan.test.Student@2a139a55
com.yikuan.test.Student@15db9742
com.yikuan.test.Student@6d06d69c
com.yikuan.test.Student@7852e922

加上toString：打印集合中的元素值

結果：

Student [name=aa, age=12]
Student [name=ww, age=14]
Student [name=qq, age=15]
Student [name=ee, age=51]

集合ArrayList---回顧toString方法