ArrayList的使用

ArrayList的使用

储存随机数字

题目要求

代码实现

import java.util.ArrayList;
import java.util.Random;

public class demo08 {
    public static void main(String[] args) {
        ArrayList<Integer> list = new ArrayList<>();
        Random r = new Random();

        for (int i = 0; i < 6; i++) {
            int num = r.nextInt(33) + 1;
            list.add(num);
        }
        System.out.println(list);


    }
}

储存自定义对象

题目要求

代码实现

import java.util.ArrayList;

public class demo01 {
    public static void main(String[] args) {
        Student one = new Student("蔡徐坤", 19);
        Student two = new Student("王一博", 20);
        Student three = new Student("易烊千玺", 23);
        Student four = new Student("王源", 21);
        ArrayList<Student> list = new ArrayList<>();
        list.add(one);
        list.add(two);
        list.add(three);
        list.add(four);
        for (int i = 0; i < list.size(); i++) {
            Student stu = list.get(i);
            System.out.println("姓名:" + stu.getName() + ",年龄:" + stu.getAge());
        }
    }
}

集合作为方法参数

题目要求

代码实现

import java.util.ArrayList;

public class demo02 {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();
        list.add("易烊千玺");
        list.add("王源");
        list.add("王俊凯");
        list.add("蔡徐坤");
        list.add("王一博");

        System.out.println(list);
        printArrayList(list);


    }

    public static void printArrayList(ArrayList<String> list) {
        System.out.print("{");
        for (int i = 0; i < list.size(); i++) {
            String s = list.get(i);
            if (i != 0) {
                System.out.print("@" + s);
            } else {
                System.out.print(s);

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


    }


}

集合作为方法的返回值

题目要求

产生一个装有20个随机数的大集合,调用方法产生一个是由大集合里面的偶数所构成的小集合

代码示例

import java.util.ArrayList;
import java.util.Random;

public class demo03 {
    public static void main(String[] args) {
        ArrayList<Integer> bigList = new ArrayList<>();
        Random r = new Random();
        for (int i = 0; i < 20; i++) {
            int num = r.nextInt(100) + 1;
            bigList.add(num);
        }
        System.out.println(bigList);
        ArrayList <Integer> smallList =getSmall(bigList);
        System.out.println("该集合有"+smallList.size()+"个偶数元素");
        System.out.println(smallList);



    }

    public static ArrayList<Integer> getSmall(ArrayList<Integer> bigList) {
        ArrayList<Integer> smallList = new ArrayList<>();
        for (int i = 0; i < bigList.size(); i++) {
            int num = bigList.get(i);
            if (num % 2 == 0) {
                smallList.add(num);
            }
        }


        return smallList;

    }
}