What Is Double Colon (::) Operator Inwards Coffee Eight - Example

The double colon (::) operator is known every bit the method reference inward Java 8. Method references are expressions which get got the same handling every bit a lambda expression, but instead of providing a lambda body, they refer to an existing method yesteryear name. For example, to impress all elements of the listing you lot tin role the forEach() method every bit follows

list.stream.forEach( s-> System.out.println(s));

but hither you lot tin supersede lambda seem amongst method reference to amend readability every bit shown below:

list.stream.forEach( System.out::println);

You tin role method reference or double colon operator to refer a static method, an instance method, or a constructor.


For referring a static method, you lot tin either role className or instanceRef, but to refer an event method of a detail object, you lot need instanceRef.

Here are to a greater extent than or less examples of method reference inward Java 8:

1. A static method (ClassName::methodName) similar Person::getAge
2. An event method of a detail object (instanceRef::methodName) similar System.out::println
3. A super method of a detail object (super::methodName)
4. An event method of an arbitrary object of a detail type (ClassName::methodName)
5. A shape constructor reference (ClassName::new) like ArrayList::new
6. An array constructor reference (TypeName[]::new) like String[]:new 

The see is that if you lot are passing a lambda seem e.g. a business office which takes a value in addition to prints inward the console than instead of passing lambda expression, only overstep the println() method of PrintStream shape which you lot can access as System.out::println.

Remeber in that place is no parenthesis when you lot refer a method using method reference or lambda seem inward Java 8.  If you lot desire to larn more, The Complete Java MasterClass is a skillful house to start with.

Real the world Example of Double Colon Operator inward Java 8

Here is a real-world illustration fo method reference using double colon operator inward Java 8. In this example, nosotros are creating a Comparator which compares individual yesteryear their age. In the offset example, nosotros get got used a lambda seem to overstep the logic to compare age, acre inward the minute describe of piece of occupation of code nosotros get got used double colon operator or method reference.

You tin encounter that the minute illustration is much to a greater extent than readable in addition to clean:

Btw, If you lot are using IDE similar Eclipse, NetBeans, or IntelliJ IDEA, the IDE volition besides propose you convert your lambda seem to method reference every bit shown in the following screenshot.

This confirms that it's a best practise inward Java 8 to convert lambda seem to a method reference or constructor reference using double colon operator. See this articles for to a greater extent than tips on when in addition to how you lot tin convert a lambda seem to method reference inward Java 8.

That's all virtually double colon operator of Java 8. As I said, it's known every bit method reference in addition to tin last used to refer an existing method yesteryear get upwards instead of using a lambda expression.  It's a  Java 8 best practise to favor method reference over lambda seem every bit it results inward to a greater extent than cleaner code.

Further Reading
example)

How to role filter() method inward Java 8 (tutorial)

20 Examples of Date in addition to Time inward Java 8 (tutorial)

How to role Stream shape inward Java 8 (tutorial)

How to form HashMap inward Java 8? (example)

How to role forEach() method inward Java 8 (example)

5 Books to Learn Java 8 from Scratch (books)

How to convert List to Map inward Java 8 (solution)

How to role peek() method inward Java 8 (example)

10 Java 8 Tutorials You must read (tutorials)

Thanks for reading this article thus far. If you lot similar this article in addition to thus delight percentage amongst your friends in addition to colleagues. If you lot get got whatsoever questions or feedback in addition to thus delight drib a note. 

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