I want to process this list and need another List of Integer with just even numbers. Prefer for-loop than while.. for(Iterator entries = myMap.entrySet().iterator(); entries.hasNext(); ) {} With this syntax the 'entries' scope is reduced to the for loop only. Also this will quite likely never be your performance bottleneck, so go for it if it makes the code more readable. References : StackoverflowThis article is contributed by Gaurav Miglani and Abhishek Verma. Here is comparison of their performances for a common data set stored in map by storing a million key value pairs in map and will iterate over map. Initialize a static Map using Java 9 Map.of(), Iterate Over the Characters of a String in Java, Java Program to Iterate Over Characters in String, Program to Iterate over a Stream with Indices in Java 8, Stream iterate(T,Predicate,UnaryOperator) method in Java with examples, How to iterate over a 2D list (list of lists) in Java, Java Program to Iterate Over Arrays Using for and foreach Loop. MIP Model with relaxed integer constraints takes longer to solve than normal model, why? (Update: I think this is no longer true.) This is not difficult at all, since you can get the stream from any collection, e.g. Not the answer you're looking for? This method is most common and should be used if you need both map keys and values in the loop. The second one is handy as it allows you to use lambdas, e.g. Java 8 allows iteration over a Map using forEach and a lambda expression as follows: myMap.forEach((k, v)->{ System.out.println("Key: " + k + " Value: " + v); }); Is it possible to iterate over a MultivaluedMap using forEach and a lambda expression? If you have a generic untyped Map you can use: These are all the possible ways of iterating HashMap. Modified 6 years ago. How do I read / convert an InputStream into a String in Java? Below is the sample code that I tried using Lambda Expression. What are the differences between a HashMap and a Hashtable in Java? You can run this program in IDE or from the command line and see the result. Java 8 Difference between map() and flatMap() in Stream API ? If it bothers you, you could even reduce it to two lookups, however, the constant factor is irrelevant for the overall time complexity, which will be constant time, if the map has a constant time lookup, like HashMap. [edit] I wrote valueSet() originally but of course entrySet() is actually the answer. We have also got stream APIs. See the original article here. This is the same logic we have used while solving coding problems to check if a given number is even or odd in Java. List or Set, by calling the stream() method, which is defined in the java.util.Collection interface. Connect and share knowledge within a single location that is structured and easy to search. Then, the map() function will do the transformation for you. We can use streams in Java 8 and above to iterate a map by passing the lambda expression to the forEach () method of the Stream interface that performs an action for each element of this stream. For example, if we want to find the sum of all of the keys and values of a map, we can write: Using MutableMap of Eclipse (CS) collections, Perfomance tests (mode = AverageTime, system = Windows8.1 64-bit, Intel i7-4790 3.60 GHz, 16GB), For a small map (100 elements), score 0.308 is the best, For a map with 10000 elements, score 37.606 is the best, For a map with 100000 elements, score 1184.767 is the best, Graphs (performance tests depending on map size), Table (perfomance tests depending on map size). The idea is that there is a list of maps and I would like to create a new list of maps, using a filter on the key. 2. I find the following code looks a bit cleaner. You can also experiment with using more map() functions or more filter() calls to make the composition longer and more sophisticated. You will see difference in the order: If I have an object implementing the Map interface in Java and I wish to iterate over every pair contained within it, what is the most efficient way of going through the map? How do I call foo with 2 String parameters for a MultivaluedMap<String, String>? Making statements based on opinion; back them up with references or personal experience. Why does Acts not mention the deaths of Peter and Paul? Iterating over Map.entrySet() using For-Each loop :Map.entrySet() method returns a collection-view(Set>) of the mappings contained in this map. That's all about how to use map and filter in Java 8. It's not them. Which was the first Sci-Fi story to predict obnoxious "robo calls"? To select just even numbers, we can use the filter() method. How do I stop the Flickering on Mode 13h? Published at DZone with permission of Javin Paul, DZone MVB. @Pureferret The only reason you might want to use an iterator is if you need to call its. For example, by using the map() function, you can convert a list of String into a List of Integer by applying the Integer.valueOf() method to each String on the input list. Many of my readers emailed me, asking to write a post about themap and filter function of Java 8, because they found it difficult to use and understand. Opinions expressed by DZone contributors are their own. How do I convert a String to an int in Java? Iterate over a Map in Java | Baeldung I have chosen the valueOf() method because of performance and caching.