Demonstration - Buggy hashcode can create a havoc in Hashmap

Demo.java

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

/**
 * Created by Anand_Rajneesh on 4/3/2017.
 */
public class Demo {

    public static void main(String[] args) {
        Map<Key,String> map = new HashMap<>();
        Key key1 = new Key(10);
        Key key2 = new Key(5);
        Key key3 = new Key(4);

        System.out.println("Key1 hashcode "+key1.hashCode());
        System.out.println("Key2 hashcode "+key2.hashCode());
        System.out.println("Key3 hashcode "+key3.hashCode());

        System.out.println("Key1 equals Key2 ? "+key1.equals(key2));
        System.out.println("Key1 equals Key3 ? "+key2.equals(key3));
        System.out.println("Key2 equals Key3 ? "+key3.equals(key2));

        map.put(key1, "key1");
        map.put(key2, "key2");

        System.out.println("Map.get key1 "+ map.get(key1));
        System.out.println("Map.get key2 "+map.get(key2));
        System.out.println("Map.get key3 "+map.get(key3));

        map.put(key3, "key3");

        System.out.println("Map.get key1 "+map.get(key1));
        System.out.println("Map.get key2 "+map.get(key2));
        System.out.println("Map.get key3 "+map.get(key3));


    }


    private static class Key{

        private final int id;

        public Key(int id) {
            this.id = id;
        }

        @Override
        public boolean equals(Object obj) {
            if(obj != null && obj instanceof Key){
                if(id < 10 && ((Key)obj).id < 10){
                    return true;
                }
                return id == ((Key)obj).id;
            }
            return false;
        }

        @Override
        public int hashCode() {
            if(id<10)
                return 0;
            else
                return 1;
        }
    }
}