Maps check for key uniqueness : Map « Utility Classes « SCJP

1. SCJP
2. Utility Classes
3. Map

import java.awt.Point;
import java.util.HashMap;
import java.util.Map;

public class MainClass {
  public static void main(String[] argv) {
    Map pointToText = new HashMap();

    pointToText.clear();
    Point p1 = new Point(1, 2);
    pointToText.put(p1, "First");
    Point p2 = new Point(1, 2);
    pointToText.put(p2, "Second");

    System.out.println(pointToText);
  }
}

{java.awt.Point[x=1,y=2]=Second}