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新概念-集合

集合是可变的数组（嗯，在我看来可以这样子认为）。不过它不能装基础数据类型

以下是集合的一些基本操作，增删改查

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import java.util.ArrayList;

public class demol1_jihe {
    public static void main(String[] args) {
        ArrayList<String> s=new ArrayList<>();
        s.add("aaa");
        System.out.println(s);
        s.add("aaa");
        s.add("bbb");
        s.add("ddd");
        System.out.println(s);
        //删除
        s.remove(0);
        System.out.println(s);
        s.remove("aaa");
        System.out.println(s);
        //改
        s.set(0,"lll");
        System.out.println(s);
        System.out.println(s.get(0));
        for (int i = 0; i < s.size(); i++) {
            String s1=s.get(i);
            System.out.println(s1);
        }
    }
}

以下是一些与集合相关的题目，进行巩固

上干货

image-20231027153816350

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import java.util.ArrayList;

public class demol1_jihe {
    public static void main(String[] args) {
        ArrayList<String> s=new ArrayList<>();
        s.add("元素一");
        s.add("元素二");
        s.add("元素三");

        for (int i = 0; i < s.size(); i++) {
            String s1=s.get(i);
            System.out.println(s1);
        }
    }
}

image-20231027154559156

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package demol3;

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;
    }
}

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package demol3;

import java.util.ArrayList;

public class demol4 {
    public static void main(String[] args) {
        ArrayList<student> s=new ArrayList<>();
        student a=new student("赵敏",18);
        student b=new student("管管",20);
        student c=new student("殷素素",21);
        s.add(a);
        s.add(b);
        s.add(c);
        System.out.println(s);
        for (int i = 0; i < s.size(); i++) {
            System.out.print(s.get(i).getName()+"\t");
            System.out.println(s.get(i).getAge());
        }
    }

}

image-20231027190454414

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package demol3;

public class student {
     String name;
    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;
    }
}

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package demol3;

import java.util.ArrayList;
import java.util.Scanner;

public class demol4 {
    public static void main(String[] args) {
        //创建集合对象
        ArrayList<student> s=new ArrayList<>();
        Scanner q=new Scanner(System.in);
        for (int i1 = 0; i1 < 3; i1++) {
            student a=new student();
            System.out.println("请输入学生姓名：");
            String name=q.next();
            System.out.println("请输入学生年龄：");
            int age=q.nextInt();
            //将你获得的数据带入期中
            a.setName(name);
            a.setAge(age);
            //将对象带入集合中
            s.add(a);

        }

      //遍历输出
        for (int i = 0; i < s.size(); i++) {
            System.out.print(s.get(i).getName()+"\t");
            System.out.println(s.get(i).getAge());
        }
    }

}

image-20231027194203320

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package demol5;

public class stu {
    private int id;
    private String username;
    private String passward;

    public stu() {
    }

    public stu(int id, String username, String passward) {
        this.id = id;
        this.username = username;
        this.passward = passward;
    }

    public int getId() {
        return id;
    }

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

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassward() {
        return passward;
    }

    public void setPassward(String passward) {
        this.passward = passward;
    }
}

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package demol5;

import java.util.ArrayList;
import java.util.Scanner;

public class demol6 {
    public static void main(String[] args) {
        ArrayList<stu> s=new ArrayList<>();
        stu a=new stu(1,"zhaoming","asfas789");
        stu b=new stu(2213124,"zgangsan","fadfa868");
        stu c=new stu(3,"xiaowu","sadas798");
        s.add(a);
        s.add(b);
        s.add(c);
        //查询当前用户信息，并返回是否
        Scanner i=new Scanner(System.in);
        System.out.println("请输入要查询的id：");
        int id=i.nextInt();
        System.out.println(exist(id,s));

    }
    //定义一个方法，判断用户输入的ID用户还在不在
    public static boolean exist(int a,ArrayList<stu> luo) {
        for (int i = 0; i < luo.size(); i++) {
            if(luo.get(i).getId()==a)return true;
        }
        return false;
    }

}

image-20231027212010803

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package demol7;

public class Phone {
    private String name;
    private int price;

    public Phone() {
    }

    public Phone(String name, int price) {
        this.name = name;
        this.price = price;
    }

    public String getName() {
        return name;
    }

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

    public int getPrice() {
        return price;
    }

    public void setPrice(int price) {
        this.price = price;
    }
}

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package demol7;

import java.util.ArrayList;

public class demol1 {
    public static void main(String[] args) {
        ArrayList<Phone> s=new ArrayList<>();
        Phone a=new Phone("小米",1000);
        Phone b=new Phone("苹果",8000);
        Phone c=new Phone("锤子",2999);
        //将数据代入
        s.add(a);
        s.add(b);
        s.add(c);
        System.out.println(Phonename(s));

    }
    public static String Phonename(ArrayList<Phone>s){
       String result="";
        for (int i = 0; i < s.size(); i++) {
           if( s.get(i).getPrice()<3000){
               result=result+s.get(i).getName()+"\t";
           }
        }
        return result;
    }
}

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