How to Sort Map by values in Java 8 using Lambdas and Stream - Example Tutorial

In past, I have shown you how to sort a HashMap by values in Java, but that was using traditional techniques of pre-Java 8 world. Now the time has changed and Java has evolved into a programming language which also has the power of functional programming. How can you take advantage of that fact to do your day to day task e.g. how do you sort a Map by values in Java using lambda expressions and Stream API. That's what you are going to learn in this article. It will serve two purposes, first, it will tell you a new way to sort a Map by values in Java, and, second and more important it will introduce you to essential Java 8 features like lambda expression and streams.

10 points about lambda expressions in Java 8

The Lambda expression is one of the important features of Java 8 but if you look from a developer's point of view, it is nothing but a way to pass code to a method in Java. Technically, it's an expression where you can define parameters and then the code which uses those parameters, similar to a method in Java, but you don't need to write boilerplate code e.g. method name, return type, argument type etc. Most of those details are inferred by compiler and JVM from the context in which lambda expression is used. Some of you question, why lambda expression was introduced in the first place? Is it just the replacement of Anonymous class? Well, the lambda expression is more than that because it also introduces functional programming in Java.

Now, Java has best of both world i.e. Object oriented programming and Functional programming which means you can write even more scalable and robust, mission critical application in Java.

How to convert Java 8 Stream to Array or ArrayList - Example Tutorial

It's relatively easy to convert a Stream to an array in Java 8 by using the toArray() method of java.util.Stream class. By using this method you can convert any type of Stream to a corresponding array e.g. a Stream of Strings can be converted into an array of String, or a Stream of integers can be converted into an array of Integers. The Stream.toArray() method is also overloaded, the one which doesn't take any parameter returns an Object[] which might not be very useful, particularly if you want to convert Stream of T to array of T. On the other hand, the overloaded version of toArray(IntFunction[] generator) returns an array containing the elements of this stream, using the provided generator function to allocate the returned array, as well as any additional arrays that might be required for a partitioned execution or for resizing.