Java ArrayList as the basis of the return value type

 Use ArrayList as the return value type
 topic: use a large collection to store 20 random numbers, and then filter the even-numbered elements among them, and place them in a small collection.
  Use a custom method to achieve
 analysis:
  1. You need to create a large collection, use To store int numbers, <Integer>
  2. Random numbers use Random nextInt ()
  3. Loop 20 times, hit random numbers into a large collection: for loop, add method
 4. Define a method for 
   screening: the base is large Collection, filter the elements that meet the requirements, get a small collection

Three elements:
 return value type: ArrayList small collection (the number of elements is uncertain)    
  Method name: getSmallList
  parameter list: ArrayList large collection (with 20 random elements)
 5. Judgment (if) is an even function: num% 2 == 0;
 6. If it is even, put it in a small set, otherwise do n’t put it
 

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

public class Text10ArrayListReturn {

	public static void main(String[] args) {
		//第一，先引入ArrayList与Random
		ArrayList<Integer> bigList=new ArrayList<>();
		Random r=new Random();
		//第二，从1~100之间抽取20个数字  与add方法存储    然后用ArrayList<Integer> 作为返回值类型  及参数bigList
		for(int i=0;i<20;i++) {
			int num=r.nextInt(100)+1;//将随机的数字放入num  从100个数字中抽取20个数字
			bigList.add(num);//将20个数字添加进去
			//System.out.println(num);
		}
 
		 ArrayList<Integer> sList = getSamllList(bigList);
		 //遍历出偶数
		 System.out.println("偶数个数"+sList.size());
		 for(int i=0;i<sList.size();i++) {
			 System.out.print("\t"+sList.get(i));
			 
		 }
	}
//  第三 这个方法，接受大集合参数，返回小集合结果
		public static ArrayList<Integer> getSamllList(ArrayList<Integer> bigList){
			//第四，创建个小集合  从大集合中20个数字筛选出偶数   也是用add方法
			ArrayList<Integer> samllList=new ArrayList<>();
			for(int i=0;i<bigList.size();i++) {//从大集合中的数据进行筛选
				int num=bigList.get (i);
				if(num%2==0) {
					samllList.add(num);//筛选的结果放在samllList  然后返回结果
				}
			}
			return samllList;
		}
}

result:
偶数个数9
8	14	66	88	74	34	24	32	24(随机)