The central interfaces of he Collections Framework are : Collection « Utility Classes « SCJP

1. SCJP
2. Utility Classes
3. Collection

java.util.Collection
java.util.List (which extends Collection)
java.util.Set (which also extends Collection)
java.util.Map (which doesn't extend Collection)

import java.util.Collection;
import java.util.Iterator;

public class MainClass {
  public static void main(String[] argv) {
    System.out.println();
  }

  public void dumpCollection(Collection c) {
    System.out.println("Collection has" + c.size() + " elements.");
    Iterator iter = c.iterator();
    while (iter.hasNext())
      System.out.println("Next element is" + iter.next());
  }

}