java集合框架复习----(1)
阅读原文时间:2023年07月08日阅读:1

文章目录

1 、集合框架思维导图

存放在java.util.*。是一个存放对象的容器。

  • 存放的是对象的引用,不是对象本身
  • 长度不固定
  • 只能存放对象


collection的使用

  • 增加元素 add();

  • 判断是否包含某个元素 contains();

  • 删除某个元素 remove();

  • 遍历元素(iterator迭代器)

    package com.zheng.demo1;

    import java.util.ArrayList;
    import java.util.Collection;
    import java.util.Iterator;

    public class MyCollection {
    public static void main(String[] args) {
    Collection c = new ArrayList();
    //增加元素
    c.add("足球");
    c.add("篮球球");
    c.add("乒乓球");
    //集合大小
    System.out.println("当前集合大小:" + c.size());
    //判断是否包含某个元素
    System.out.println(c.contains("足球"));
    //删除元素
    c.remove("足球");
    System.out.println("删除一个元素之后大小:" + c.size());
    System.out.println("===============");

        //打印,增强for循环
        for (Object obj : c) {
            System.out.println("增强for循环取值:"+obj);
        }
        System.out.println("==============");
    //迭代器形式
    Iterator it = c.iterator();
    while (it.hasNext()){//判断有无下一个元素
        Object obj=it.next();//取值
        System.out.println("iterator取值:"+obj);
    
    }
    }

    }

Iterator:迭代器

  • hasNext(); 查看是否有下一个元素。有为true,无为false
  • next(); 取出下一个元素的值
  • remove(); 删除当前元素

在JAVA中,所有的对象都有toString方法;方便打印

通过添加一个对象到collection集合中

实体类

package com.zheng.demo1;

public class Student {
    private int id;
    private String name;
    private String address;

    public Student() {

    }

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

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", address='" + address + '\'' +
                '}';
    }
}

加入到集合

package com.zheng.demo1;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;

public class MyCollection1 {
    public static void main(String[] args) {
        //创建容器
        Collection<Student> students = new ArrayList<Student>();

        //创建对象
        Student student1 = new Student(1, "小明", "北京");
        Student student2 = new Student(2, "小红", "河南");
        Student student3 = new Student(3, "小黑", "深圳");
        Student student4 = new Student(4, "小蓝", "上海");

        //添加对象到容器中
        students.add(student1);
        students.add(student2);
        students.add(student3);
        students.add(student4);

        //查看
        System.out.println(students.toString());

        System.out.println("=========增强for循环输出=========");
        //增强for循环输出
        for (Student student : students) {
            System.out.println(student.toString());

        }

        System.out.println("=========迭代器输出=========");
        //迭代器输出
        Iterator<Student> iterator = students.iterator();
        while (iterator.hasNext()) {
            System.out.println(iterator.next());
        }

    }
}