Java: Implement Bidirectional Map

Bidirectional map preserves the uniqueness of its values as well as that of its keys. You can get the value from key, and key from value.

By extending any of the existing maps implementations, you can create a bidirectional map.

BiMap.java

package com.sample.app;

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

public class BiMap<K, V> extends HashMap<K, V> {
 private static final long serialVersionUID = 1L;
 public Map<V, K> inversedMap = new HashMap<V, K>();

 public K getKey(V value) {
  return inversedMap.get(value);
 }

 @Override
 public int size() {
  return this.size();
 }

 @Override
 public boolean isEmpty() {
  return this.size() > 0;
 }

 @Override
 public V remove(Object key) {
  V val = super.remove(key);
  inversedMap.remove(val);
  return val;
 }

 @Override
 public V get(Object key) {
  return super.get(key);
 }

 @Override
 public V put(K key, V value) {
  inversedMap.put(value, key);
  return super.put(key, value);
 }

}

App.java

package com.sample.app;

public class App {

 public static void main(String args[]) {
  BiMap<Integer, Integer> map = new BiMap<>();

  map.put(10, 20);
  map.put(11, 21);

  System.out.println("10 -> " + map.get(10));
  System.out.println(map.getKey(21) + " -> 21");
 }
}

Output

10 -> 20

11 -> 21

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