2 Examples of Streams with Collections in Java 8

Finally Java 8 is here, after more than 2 years of JDK 7, we have a much expected Java 8 with lots of interesting feature. Though Lambda expression is the most talked item of coming Java 8 release, it wouldn't have been this much popular, if Collections were not improved and Stream API were not introduced. Java 8 is bringing on new Streams API java.util.stream package, which allow you to process elements of Java Collections in parallel. Java is inheritably sequential and there is no direct mean to introduce parallel processing at library level, stream API is going to fill that gap. By using this, you can filter elements of collection on given criterion e.g. if you have a List of orders, you can filter buy orders with sell orders, filter orders based upon there quantity and price and so on. You can also perform two of most popular functional programming functions e.g. map and reduce. java.util.stream class provides function such mapToInt(), mapToLong(), and map function to apply an operation on all elements of Collections. By the way, these are just few of gems of Stream API, I am sure you will find several more, when you start exploring lambda expression and java.util.stream package. In this tutorial, we will see 2 examples of using Java 8 Stream with Collections classes. I have chosen List for these example, but you can use any Collection e.g. Set, LinkedList etc. By the way, use of Stream is not limited to Collections only, you can even use an array, a generator function, or an I/O channel as source. In most cases, a Stream pipeline in Java 8 consists a source, followed by zero or more intermediate stream operations e.g. filter() or map(); and a terminal operation such as forEach() or reduce().

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10 Example of Lambda Expressions and Streams in Java 8

Java 8 release is just a couple of weeks away, scheduled at 18th March 2014, and there is lot of buzz and excitement about this path breaking release in Java community. One of feature, which is synonymous to this release is lambda expressions, which will provide ability to pass behaviours to methods. Prior to Java 8, if you want to pass behaviour to a method, then your only option was Anonymous class, which will take 6 lines of code and most important line, which defines the behaviour is lost in between. Lambda expression replaces anonymous classes and removes all boiler plate, enabling you to write code in functional style, which is some time more readable and expression. This mix of bit of functional and full of object oriented capability is very exciting development in Java eco-system, which will further enable development and growth of parallel third party libraries to take advantage of multi-processor CPUs. Though industry will take its time to adopt Java 8, I don't think any serious Java developer can overlook key features of Java 8 release e.g. lambda expressions, functional interface, stream API, default methods and new Date and Time API. As a developer, I have found that best way to learn and master lambda expression is to try it out, do as many examples of lambda expressions as possible. Since biggest impact of Java 8 release will be on Java Collections framework its best to try examples of Stream API and lambda expression to extract, filter and sort data from Lists and Collections. I have been writing about Java 8 and have shared some useful resources to master Java 8 in past. In this post, I am going to share you 10 most useful ways to use lambda expressions in your code, these examples are simple, short and clear, which will help you to pick lambda expressions quickly.

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