Loop over Map Implementation in Java

This post discusses basic methods to loop over Map in Java. Using following methods, you can loop over any Map implementation such as HashMap, LinkedHashMap, TreeMap etc…

Initialization

Lets initialize a HashMap containing country code and country name as below.

        
        // Initialize Hashmap
	Map<String, String> countryCodes = new HashMap<String, String>();
		
	// Load Hashmap
	countryCodes.put("AUS", "Australia");
	countryCodes.put("CAN", "Canada");
	countryCodes.put("PAK", "Pakistan");
	countryCodes.put("INR", "India");

    

Method 1: Iterate and remove value from Map

THIS IS THE ONLY METHOD WHICH CAN ITERATE OVER MAP AND REMOVE ELEMENT FROM UNDERLYING MAP INSTANCE WHILE ITERATION. All other methods can iterate over Map elements, but they does not allow removing element while iteration.

        
        //Method 1: Iterate and remove value from Map
		Iterator<Map.Entry<String, String>> mapIterator = countryCodes.entrySet().iterator();
		while (mapIterator.hasNext()) {
			Map.Entry<String, String> entry = mapIterator.next();
			System.out.println("Key: "+ entry.getKey() + " => Value : "+ entry.getValue());
			if(entry.getKey().equalsIgnoreCase("PAK"))
				mapIterator.remove();
		}

		// Console
		/*
			Key: AUS => Value : Australia
			Key: INR => Value : India
			Key: PAK => Value : Pakistan
			Key: CAN => Value : Canada
		*/
    

Method 2: Loop over key and values

If you need key and value of Map elements in your loop, then use this method.

        
        // Method 2: Loop over key and values
		for(Map.Entry<String, String> entry : countryCodes.entrySet())
		{
			System.out.println("Key: "+ entry.getKey() + " => Value : "+ entry.getValue());
		}

		// Console
		/*
			Key: AUS => Value : Australia
			Key: INR => Value : India
			Key: CAN => Value : Canada
		*/

    

Method 3: Loop over keys

This method iterate over keys of a HashMap.

        
        // Method 3: Loop over keys
		for(String key : countryCodes.keySet())
		{
			System.out.println("Key: "+ key);
		}

		// Console
		/*
			Key: AUS
			Key: INR
			Key: CAN
		*/

    

Method 4: Loop over values

Use this method if you need only value of Map elements in your loop.

        
        // Method 4: Loop over values
		for(String value : countryCodes.values())
		{
			System.out.println("Value: "+ value);
		}

		// Console
		/*
			Value: Australia
			Value: India
			Value: Canada
		*/

    

References

Map in Java
Iterator