Tip: Understanding the Collection.removeIf Method

Collection.removeIf is a very powerful method that acts on a condition. In the code sample below, there is a list which has a few elements in it and the condition is to list all elements that are not even numbers. The condition is specified in the Predicate.

Code snippet:

import java.util.function.Predicate;
import java.util.*;

public class CollectionsRemoveIf
{
   public static void main(String args[])
   {
      CollectionsRemoveIf collectionsRemoveIf = new CollectionsRemoveIf();
      collectionsRemoveIf.proceed();
   }
   
   private void proceed()
   {
      List numbers = new ArrayList();
      numbers.add(1);
      numbers.add(3);
      numbers.add(5);
      numbers.add(6);
      numbers.add(7);
      numbers.add(8);
      
      Predicate removeEvenNumbers = i - i % 2 == 0;

      System.out.println("Original list...");
      for (int numberValue : numbers) {
         System.out.println(numberValue);
      }      
      
      //Predicate, the condition, is being added to the removeIf.
      numbers.removeIf(removeEvenNumbers);
      
      System.out.println("Odd numbers list...");
      for (int numberValue : numbers) {
         System.out.println(numberValue);
      }      
   }
}

/*

Expected output:

[root@mypc]# java CollectionsRemoveIf
Original list...
1
3
5
6
7
8
Odd numbers list...
1
3
5
7

*/

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