Java 8 has has made some improvements in collections framework such as a new forEach loop, better type inference etc. We will list out those features here.

The forEach method

The default forEach method of the Iterable interface performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception. 

Signature of the methiod is: void forEach(Consumer<? super T> action) [node:read-more:link]

Before Java 8, you could only use final variables from a surrounding class in an anonymous inner class. In Java 8, within anonymous class (or lambda expressions) you can use effectively final variables: not declared as final but only assigned once. 

Important points about accessing variables from within an anonymous inner class (or lambda expression) [node:read-more:link]

Java 8 allows you to write lambda expressions in few varying syntaxes. Let us quickly see those here.

With no arguments

Runnable r = () -> System.out.println(“H”);

Only one argument: with or without parenthesis

ActionListener al1 = (event) -> System.out.println(“Button clicked”);

ActionListener al2 = event -> System.out.println(“Button clicked”);

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Lambda expressions implement an interface with only one single abstract methodl. Such interfaces are called as functional interfaces. Since the interface has only one single method (function), passing across that interface implementation gives the impression of passing across that function. Already existing interfaces in Java such as Runnable, Comparator, ActionListener are already functional interfaces, as they have only one abstract method. We will see how we can use lambda expressions with those existing interfaces.

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Before Java 8, interfaces could only have abstract methods and constants. Java 8 allows you to have default as well as static methods inside an interface. This was mainly done for interface unlocking: Now you can add methods to an interface without needing the implementing classes to change.

Default methods

You can add an instance method to an interface through the keyword default.

They are also public similar to the abstract methods. 

Default methods are inherited by subclasses and can be overriden. [node:read-more:link]