import java.util.Map;

import java.util.HashMap;

public class HashOverrideDemo{

public static void main(String[] args){

Point p1 = new Point(10,20);

Point p2 = new Point(20,30);

Point p3 = new Point(10,20);

// Test reflexivity

System.out.println(p1.equals(p1));

// Test symmetry

System.out.println(p1.equals(p2));

System.out.println(p2.equals(p1));

// Test transitivity

System.out.println(p2.equals(p3));

System.out.println(p1.equals(p3));

// Test nullability

System.out.println(p1.equals(null));

// Extra test to further prove the instanceof operator's usefulness

System.out.println(p1.equals("abc"));

Map<Point, String> map = new HashMap<Point, String>();

map.put(p1, "first point");

System.out.println(map.get(p1));

// Test the hashCode implementation for Point and HashMap.

System.out.println(map.get(new Point(10,20)));

// The last two lines of output is the same.

}

}

class Point{

private int x, y;

Point(int x, int y){

this.x = x;

this.y = y;

}

int getX(){

return x;

}

int getY(){

return y;

}

public boolean equals(Object o){

if(!(o instanceof Point)){

return false;

}

Point obj = (Point)o;

return this.x == obj.x && this.y == obj.y;

}

public int hashCode(){

int hashCode = 19; // Choose an arbitrary non-zero number

int hc = x;

hashCode = hashCode*31 + hc;

hc = y;

hashCode = hashCode*31 + hc;

return hashCode;

}

}