This is what I’ve written so far, how do I implement prime_check into prime_array? I’m a beginner so it’d be helpful if you could keep it simple.

The question –
Write a Java function that takes as input a dynamic list and returns a dynamic list of prime numbers (you need to implement the function prime_check(int num)).

    import java.util.ArrayList;
    import java.util.Arrays;
    import java.util.List;

    public class notes {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        
        ArrayList <Integer> listA2=new ArrayList<Integer(Arrays.asList(5,6,7,8,10,13,17,19,20,26,12,31));
        System.out.println(prime_array(listA2));
    } 
    
    public static boolean prime_check(int num) {
        
        boolean primecheck = true; 
        if(num <= 1) {
            primecheck = false; 
            return primecheck;
        }
        else {
            for (int i = 2; i<= num/2; i++) {
                if ((num % i) == 0) {
                    primecheck = false;  
                    break;
                }
            }
            return primecheck;
        }
        
    }

    public static ArrayList<Integer> prime_array(ArrayList<Integer> listA2) {
        
        ArrayList <Integer> nums1=new ArrayList<Integer>();
        
        for (int n1: listA2) {
            System.out.println(prime_check(n1));
            if ( = true) {
                nums1.add(n1);
            }
                
        }
        
        return nums1;
        
    }
}

>Solution :

You were very close to a solution. Try with this:

public static List<Integer> prime_array(List<Integer> listA2) {
    
    ArrayList <Integer> nums1=new ArrayList<Integer>();
    
    for (int n1: listA2) {
        if (prime_check(n1) == true) {
            nums1.add(n1);
        }
            
    }
    
    return nums1;
    
}