Guava BiMap Example (Bidirectional Map)

Guava BiMap

A special type of collection that ensures uniqueness of both keys and values. A BiMap or Bidirectional Map ensures that all values are unique — this ensures that all values are a set. I would best explain BiMap as having a mapping of keys to values and another mapping of values to keys. Such that, each set must contain unique elements.

Methods available to BiMap

@GwtCompatible
public interface BiMap<K,V>
extends Map<K,V>

BiMap Implementations

There are four implementation classes available for BiMap:

• EnumBiMap
• EnumHashBiMap
• HashBiMap
• ImmutableBiMap

Java Example using Guava BiMap

In this BiMap Example we are using HashBiMap to create a BiMap of States and their Capitals called StateCapitals. We then populate our stateCapitals BiMap with all of our states and their respective capitals. The two methods I have created enable us to pass either the key and return the respective value as is the case in the printCapitalOfState method. Additionally, we can pass the value of a mapping and return the key as is the case in the printStateOfCapital method using the inverse() method.

package com.avaldes;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.google.common.collect.BiMap;
import com.google.common.collect.HashBiMap;


public class GuavaBiMapExample {
  private static BiMap<String, String> stateCapitals = HashBiMap.create();

  public static void main(String[] args) {
    Logger logger = LoggerFactory.getLogger(GuavaBiMapExample.class);
    
    // Let's create a BiMap containing states and their respective capitals
    // eg. New Jersey -> Trenton
    
    logger.info("Adding some states and their capitals...");

    stateCapitals.put("Alabama", "Montgomery");
    stateCapitals.put("Alaska", "Juneau");
    stateCapitals.put("Arizona", "Phoenix");
    stateCapitals.put("Arkansas", "Little Rock");
    stateCapitals.put("California", "Sacramento");
    stateCapitals.put("Colorado", "Denver");
    stateCapitals.put("Connecticut", "Hartford");
    stateCapitals.put("Delaware", "Dover");
    stateCapitals.put("Florida", "Tallahassee");
    stateCapitals.put("Georgia", "Atlanta");
    stateCapitals.put("Hawaii", "Honolulu");
    stateCapitals.put("Idaho", "Boise");    
    stateCapitals.put("Illinois", "Springfield");   
    stateCapitals.put("Indiana", "Indianapolis");   
    stateCapitals.put("Iowa", "Des Moines");    
    stateCapitals.put("Kansas", "Topeka");    
    stateCapitals.put("Kentucky", "Frankfort");   
    stateCapitals.put("New Jersey", "Trenton");
    stateCapitals.put("New York", "Albany");
    
    System.out.println("\n--[States to Capitals]----");
    printCapitalOfState("Arizona");
    printCapitalOfState("Hawaii");
    printCapitalOfState("New Jersey");
    printCapitalOfState("Florida");
    printCapitalOfState("Connecticut");
    
    System.out.println("\n--[Capitals to States]----");
    printStateOfCapital("Springfield");
    printStateOfCapital("Topeka");
    printStateOfCapital("Little Rock");
    printStateOfCapital("Albany");
    printStateOfCapital("Montgomery");
    
  }

  public static void printCapitalOfState(String state) {
    if (stateCapitals.containsKey(state)) {
      System.out.println("State " + state +", capital is: " + stateCapitals.get(state));
    } else {
      System.out.println("State not found...");
    }
  }
  
  public static void printStateOfCapital(String capital) {
    if (stateCapitals.containsValue(capital)) {
      System.out.println("Capital " + capital +", state is: " + stateCapitals.inverse().get(capital));
    } else {
      System.out.println("Capital not found...");
    }
  }
}

That’s It!

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