![]() ![]() How to convert a List with Duplicates into Map in JDK 8 We have used a lambda expression to simplify the code. I have passed the method Collectors.toMap(), which means elements will be collected in a Map, where the key will be ISBN code and value will be the object itself. All the magic of how to collect elements happening in this method. In the above code example, the stream() method returns a stream of Book object from the list, and then I have used collect() method of Stream class to collect all elements. Now, let's see how we can do the same in Java 8 by using lambda expression and Stream API, here is my first attempt: It's clear, concise, and self-explanatory, but iterative. This is the best way to convert a List to Map in pre-JDK 8 worlds. You can see we have iterated through the List using enhanced for loop of Java 5 and put each element into a HashMap, where ISBN code is the key, and the book object itself is the value. Here is how you can convert a List to Map in Java 5, 6 or 7: This comparative analysis will help you to learn the concept and Java 8 API better. Now, let's see different ways to solve this problem in the pre-JDK 8 worlds and in Java 8. It's one of the better books full of non-trivial examples and once you went through that you won't need to lookup Google for your day-to-day task in Java 8.Īnd, If you are serious about improving Java functional programming skills then I highly recommend you check out the Learn Java Functional Programming with Lambdas & Streams by Rang Rao Karnam on Udemy, which explains both Functional Programming and Java Stream fundamentals in good detail In a similar note, if you have just started learning Java 8 and come here to solve a problem you are facing in your day to day life while converting a Java SE 6 or 7 code to Java 8, then I suggest going through a book like Java SE 8 for Really Impatient. Remember, the Map returned by Collector is not necessarily HashMap or LinkedHashMap, if you want to use any special Map type, you need to tell the Collector about it as shown in the second example. In the past, we have seen how to use the oupingBy() method to group elements in Set and In this article, we will use Collectors.toMap() method to convert a List of an object into a Map in Java. Since it's an iterative approach and if you are looking for a functional solution then you need to use the stream and lambda expression, along with some utility classes like Collectors, which provides several useful methods to convert Stream to List, Set, or Map. Hello guys, suppose you have a list of objects, List and you want to convert that to a Map, where a key is obtained from the object and value is the object itself, how do you do it by using Java 8 stream and lambda expression? Prior to Java 8, you can do this by iterating through the List and populating the map by keys and values. ![]()
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |