However, if you love the Lambda style of Java 8, you can use the foreach, and for the remaining purpose, you can choose 2 remaining ways. Key : 1 Value : Jan Key : 2 Value : Feb Key : 3 Value : Mar Key : 4 Value : Apr Key : 5 Value : May Key : 6 Value : Jun Example 2. Since we are only using methods from java. You can use it to print or manipulate the data. In this article, we will discuss all of them and also look at their advantages and disadvantages. Try to process your emails for some strange service.
HashMaps can store null values. Each key is associated with one value. But there is plenty of legacy code out there still doing this. This iteration is less efficient. HashMap — Used to create a default HashMap.
First of all, we cannot iterate a Map directly using , because Map are not Also before going further, you must know a little-bit about interface. We get the entry set with entrySet method and from the entry set, we get the stream with the stream method. In the next example, we iterate over a key set with an iterator while using HashMap's keySet method, which returns a Set view of the keys contained in this map. In this tutorial, we have shown how to iterate over a HashMap in Java. HashMap iteration with enhanced for loop Enhanced for loop, introduced in Java 5, can be used to iterate over a HashMap. There are generally five ways of iterating over a in Java. Since another call is required to get the mapped values this way of looping a HashMap is less efficient in case you need both keys and values.
That is not too much in fact. Related Post: We know that returns a set of key-value mappings contained in the map. Conclusions The tutorial has illustrated how to iterate over a HashMap in Java 8 by different ways, by using forEach function introduced in Java 8, for loop, Iterator and looping through the key Set of the Map. HashMaps take more memory because for each value there is also a key. Entry object key and value can be retrieved using getKey and getValue method.
The only way to obtain a reference to a single map entry is from the iterator of this collection view. In first method we use for-each loop over Map. This method should be avoided. The entries in the set are actually object of type Map. Using entrySet method Using entrySet method you get the set view of the mappings stored in the HashMap in the form of Map. This makes it also the fastest way to loop over HashMap in Java. Options for iterating a Java HashMap As you can see from the above methods you either get a Set with Map.
It performs the given action for each remaining element until all elements have been processed. It gives you full control over the keys and values in the map. Notify me of new posts by email. Now we can get the key-value pair easily using the getKey and getValue method. In the below code we will get EntrySet from the entrySet method, from the entrySet we will get the Stream through the stream method which we will be iterating using forEach. If you are stuck with older version of Java less than 5 or planning to remove entries during iteration you have to use method 3. In next section, we will see code using Iterator, which can help you for removal of entries from Map.
If you have any doubt or any suggestions to make please drop a comment. Once we have the Iterator, we can pass the method reference System. Should be used if you need both map keys and values in the loop. Since those are all sets, similar iteration principles apply to all of them. Get latest update on and.
Small tips and possible you may get in the future. It is all about scale! In such a case, we need an additional loop. The will invoke the iterator method internally. This was the default approach in Java 1. It is called for-each loop and is available to any object implementing Iterable Interface. Simply put, we can extract the contents of a Map using keySet , valueSet or entrySet. It is 1k seconds extra ~16 minutes.
Deletion and insertion operations take constant time. Each entry has a key string and list value. Also gone now is the cast, so this code smells better! Example code to iterate a HashMap in Java Here is an example using all of the above mentioned methods for iterating a HashMap. Examples Different ways to loop a Map LoopMap. References Below are other related articles for your references:.