![]() ("Key : " e.getKey() " value : " e.getValue())įor (Map.Entry entry : students. Students.entrySet().stream().forEach(e -> Value: Iterating Maps in Java: using stream() in JAVA 8 ![]() using values() for iteration over keys using keySet() for iteration over keys So, when only keys or values from the Map is required, you can iterate over keySet or values using for-each loops. Map.keySet() method returns a Set view of the keys contained in this Map and Map.values() method returns a collection-view of the values contained in the Map. Key : 3 value : Cathy Iterating over keys or values using keySet() and values() method using for-each loop This method is helpful when the number of entries is not known. Iterating over entries using For-Each loop ![]() Let us have a look at the different ways to iterate Maps in Java. We cannot iterate a Map directly using iterators, because Map is not Collection so we use some other ways to iterate Maps which are described in detail further in this blog. Each key can be mapped to at most one value. Once stored in a Map, you can later look up a particular value by using just the key of assigned to that value. a Java Map can store pairs of keys and values where each key is linked to a specific value. The Java Map interface,, represents the mapping between a key and a value i.e. What is a Map in JAVA?Ī Map is one of the most important Data Structures in Java. Iterating over keys or values using keySet() and values() method using for-each loopīefore starting with the methods to iterate Maps, let us first have a brief look at what is a Map in Java.Iterating over entries using For-Each loop.The blog consists of the following topics: ("\n- Iterate using Map.entrySet and forEach loop -") įor (Map.Entry moviePair : map.In this blog on “iterate Maps in Java”, you will be learning about various ways of iterating Maps and will analyze the methods so that it is easier for you to make a choice among them according to your requirements. Let’s first use Map.entrySet and forEach to traverse the map entries. However, there are other ways to get both the keys and values much faster. If you just need the keys in a map, use of Map.keySet is a good option. This approach will also invoke two operations for each entry just like the forEach approach shown earlier. Iterator actors = map.keySet().iterator() ("\n- Iterate using Map.keySet and Iterator -") ![]() However, this approach is costly as it invokes two operations for each entry – first to get the next key and then to fetch the value using get.Ī similar approach is to use Iterator over Map.keySet instead of forEach loop. Using a for loop to iterate through a HashMap In the code below, hashmap.entrySet () is used to return a set view of the mapped elements. This is a convenient approach to scan all the entries in the map. The loop iterates over Map.keySet and we get the corresponding value using Map.get. ("\n- Iterate using Map.keySet and forEach loop -") Let’s first consider the use of forEach loop. Map.keySet provides different options to iterate over Map. Let’s see other methods of getting all the keys and values from the map. ("- Iterate using Java 8 forEach loop -") One of the easiest Map iteration mechanisms is to use forEach from Java8: // Java 8 forEach loop Map.put("Matthew McConaughey", "Interstellar") Map.put("Charlie Chaplin", "City Lights") Map.put("Marlin Brando", "The Godfather") Map.put("Arnold Schwarznegger", "Terminator") Map.put("Daniel Craig", "No Time To Die") Map IterationĬonsider, a map of some famous Hollywood movies with the name of lead actor as the key: map = new HashMap() In this article I will cover some techniques to efficiently iterate over Map entries, highlighting when it may be beneficial to use a particular technique. HashMap and TreeMap are the most commonly used Map implementations. There is a rich pool of Map implementations available: However, that is not the case, and the Map interface behaves differently from the Collection interface. Map interface is often thought of as being a subtype of the Collection interface. The Map interface in Java is available in java.util package and is used to represent mapping between a key and a value.
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