从 java 中的 arraylist 返回所有奇数

Question

In the constructor I used the random function to print out 20 random numbers from 1 to 99 into the ArrayList(iList). Then I made a method that will get all odd numbers from the random numbers that generated into iList and output the odd numbers put it isn't outputting the odd numbers for some reason. Could someone help me fix this.

My code below:

import java.util.*;
import java.util.Random;

public class ArrayList_Practice
{
    
    int List;
    ArrayList<Integer> iList=new ArrayList<Integer>();
    Random rand = new Random();

    public ArrayList_Practice() {    
        for(int i = 0; i < 20; i++)
        {
            List = rand.nextInt(100);
            iList.add(List);
        }
        System.out.println(iList);
    }

    public void getoddNumber() {
        int thesizeof = iList.size();
        int s = 0;

        for(int i = 0; i < thesizeof; i++){
           if(thesizeof % 2 == 1){
                thesizeof = iList.remove(iList.size()-1);
                iList.remove(iList.size()-1);
                System.out.println(iList);
           }
        }
    }
}

Answer 1

You compare the sitze of the list,not the index. And because the original list size is even you never walk into the if block.

       if(i % 2 == 1){
            System.out.println(iList.get(i));
       }  

BTW: you should learn how to debug your code.

Answer 2

If you want to print the odd numbers (and not the numbers at the odd indices) the you should do it like this.

List<Integer> list = List.of(1,2,3,10,12,14,17,18,20,19);
for(int val : list) {
   if (val % 2 == 1) {
      System.out.print(val + " ");
   }
}

Prints

1 3 17 19

If you want the numbers at odd indices, then you don't need to test if they are odd, just print every other one starting at 1.

for (int k = 1; k < list.size(); k+=2) {
            System.out.print(list.get(k));
}

Prints

2 10 14 18 19