java基础——集合Arraylist

一、概念

ArrayList 类是一个可以动态修改的数组，与普通数组的区别就是它是没有固定大小的限制，我们可以添加或删除元素。

二、创建方式

import java.util.ArrayList; // 引入 ArrayList 类

ArrayList<E> objectName =new ArrayList<>();　 // 初始化

• E: 泛型数据类型，用于设置 objectName 的数据类型，只能为引用数据类型。
• objectName: 对象名。

三、使用方法

import java.util.ArrayList;
import java.util.List;

public class CollectionExample {
    private List<String> items;

    // 构造函数，初始化集合
    public CollectionExample() {
        items = new ArrayList<>();
    }

    // 添加元素
    public void addItem(String item) {
        items.add(item);
        System.out.println(item + " has been added.");
    }

    // 删除元素
    public void removeItem(String item) {
        if (items.remove(item)) {
            System.out.println(item + " has been removed.");
        } else {
            System.out.println(item + " not found.");
        }
    }

    // 访问元素
    public String getItem(int index) {
        if (index >= 0 && index < items.size()) {
            return items.get(index);
        } else {
            return "Index out of bounds.";
        }
    }

    // 更改元素
    public void updateItem(int index, String newItem) {
        if (index >= 0 && index < items.size()) {
            items.set(index, newItem);
            System.out.println("Item at index " + index + " has been updated to " + newItem + ".");
        } else {
            System.out.println("Index out of bounds.");
        }
    }

    // 打印所有元素
    public void printItems() {
        System.out.println("Current items in the collection: " + items);
    }

    // 主方法用于测试
    public static void main(String[] args) {
        CollectionExample collection = new CollectionExample();
        
        // 添加元素
        collection.addItem("Apple");
        collection.addItem("Banana");
        collection.addItem("Orange");

        // 打印当前元素
        collection.printItems();

        // 访问元素
        System.out.println("Item at index 1: " + collection.getItem(1));

        // 更新元素
        collection.updateItem(1, "Mango");

        // 打印更新后的元素
        collection.printItems();

        // 删除元素
        collection.removeItem("Apple");
        collection.printItems();
    }
}

运行结果： 

Apple has been added.
Banana has been added.
Orange has been added.
Current items in the collection: [Apple, Banana, Orange]
Item at index 1: Banana
Item at index 1 has been updated to Mango.
Current items in the collection: [Apple, Mango, Orange]
Apple has been removed.
Current items in the collection: [Mango, Orange] 

四、 示例

1、添加字符串，并进行遍历

import java.util.ArrayList;
public class ArraylistDemo {
  public static void main(String[] args) {
    ArrayList<String> list = new ArrayList<>();
    list.add("点赞");
    list.add("收藏");
    list.add("转发");
    System.out.print("[");
    for (int i = 0; i < list.size(); i++) {
      if(i==list.size()-1){
        System.out.print(list.get(i));
      }else{
        System.out.print(list.get(i)+",");
      }

    }
    System.out.println("]")；

  }
}

 [点赞,收藏,转发]

2、添加数字，并进行遍历

package week6_String;

import java.util.ArrayList;
public class ArraylistDemo {
  public static void main(String[] args) {
    //1.创建元素
    ArrayList<Integer> list2 =new ArrayList<>();
    //2.添加元素
    list2.add(1);
    list2.add(2);
    list2.add(3);
    list2.add(4);
    list2.add(5);
    System.out.print("[");
    for (int i = 0; i < list2.size(); i++) {
      if(i==list2.size()-1){
        System.out.print(list2.get(i));
      }else{
        System.out.print(list2.get(i)+",");
      }

    }
    System.out.println("]");

  }
}

 [1,2,3,4,5]

 3、添加学生对象并遍历

package week5_class_test;

import java.util.ArrayList;

public class Test_student {
  public static void main(String[] args) {
    //1.创建集合
    ArrayList<Student> list = new ArrayList<>();

    //2.创建学生对象
    Student s1 = new Student("zhangsan",23);
    Student s2 = new Student("andy",34);
    Student s3 = new Student("lyla",24);
    Student s4 = new Student("tina",26);
    Student s5 = new Student("bella",27);
    //3.添加元素
    list.add(s1);
    list.add(s2);
    list.add(s3);
    list.add(s4);
    list.add(s5);

    //4.遍历集合
    for (int i = 0; i < list.size(); i++) {
      Student stu =list.get(i);
      System.out.println(stu.getName()+","+stu.getAge());
    }

  }
}

zhangsan,23
andy,34
lyla,24
tina,26
bella,27