boolean containsKey(Object key) Returns true if the Map associates some value with key. : Map « Utility Classes « SCJP

1. SCJP
2. Utility Classes
3. Map

import java.util.HashMap;
import java.util.Map;

public class MainClass {
  public static void main(String[] argv) {
    Map map = new HashMap();
    map.put("key", "value");

    System.out.println(map.containsKey("key"));
  }
}

true