Collection: addAll(Collection c) Adds every element of c to this collection : Collection « Utility Classes « SCJP

1. SCJP
2. Utility Classes
3. Collection

import java.util.ArrayList;
import java.util.Collection;

public class MainClass {
  public static void main(String[] argv) {
    Collection collection1 = new ArrayList();
    collection1.add("1");

    Collection collection2 = new ArrayList();
    collection2.add("2");

    collection1.addAll(collection2);

    System.out.println(collection1);
  }
}

[1, 2]