Map: clear()

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

public class Main {
  public static void main(String[] a) {
    Map<String,String> map = new HashMap<String,String>();
    map.put("key1", "value1");
    map.put("key2", "value2");
    map.put("key3", "value3");
    map.clear();

    System.out.println(map);
  }
}