package bao;

import java.util.ArrayList;
import java.util.Objects;

public class Test {
    public static void main(String[] args) {
        //创建对象
        ArrayList<String> a = new ArrayList<>();
        //1.增
        a.add("今天");
        a.add("上课");
        a.add("迟到了");
        a.add("555");
        System.out.println(a);//[今天, 上课, 迟到了, 555]

        //2.1删--指定值
        a.remove("今天");
        System.out.println(a);//[上课, 迟到了, 555]
        //2.2删--索引值
        a.remove(1);
        System.out.println(a);//[上课, 555]

        //3.改--索引值
        a.set(0,"我好想放假啊");
        System.out.println(a);//[我好想放假啊, 555]

        //4.查--索引值
        String c = a.get(0);
        System.out.println(c);//我好想放假啊

        //5.遍历全部元素
        for (int i = 0; i < a.size(); i++) {
            String h = a.get(i);
            System.out.println(h);//我好想放假啊   555
        }
    }
}

运行结果

[今天, 上课, 迟到了, 555]
[上课, 迟到了, 555]
[上课, 555]
[我好想放假啊, 555]
我好想放假啊
我好想放假啊
555

2.进阶例子

创建自定义对象

1.先创建一个java bean类

2.正常创建对象步骤

java bean类

package bao;
//javabean类
public class Student {
    //javabean需要的↓
    //私有成员变量
    //构造方法
    //set和get

    //1.私有成员变量
    private String name;
    private int age;

    //2.快捷键生成构造方法
    public Student() {
    }

    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }

    //3.快捷键生成set和get
    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 bao;
import java.util.ArrayList;
//测试集合类
public class Test {
    public static void main(String[] args) {
        //1.创建自定义学生集合
        ArrayList<Student> a = new ArrayList<>();

        //2.创建元素对象
        Student s1 = new Student("张三",18);
        Student s2 = new Student("李四",19);
        Student s3 = new Student("王五",20);
        Student s4 = new Student("老六",21);

        //3.增，把对象元素添加到集合里面
        a.add(s1);
        a.add(s2);
        a.add(s3);
        a.add(s4);
        //获取集合中的元素，只能用遍历形式获取
        for (int i = 0; i < a.size(); i++) {
            Student stu = a.get(i);
            System.out.println(stu.getName()+","+stu.getAge());
        }
    }
}

运行结果