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Java method references recap

In the last post I reviewed Java lambda expressions. They represent a concise syntax to implement functional interfaces.

Enter Java method references. They represent a concise syntax to implement functional interface using existing methods. Like with lambda expressions, referenced methods are not allowed to throw checked exceptions.

Syntax

It’s simply “class-or-instance name” “::” “method name”, like

Types of method references

Reference to a static method

Static methods are referenced using the class name like in the example above.

Reference to an instance method of a particular object

Methods of a particular object are referenced using the variable name of that object:

Reference to an instance method of an arbitary object of a particular type

Instead of using an already existing object you can just state the class and a non-static method. Then the instance is an additional parameter. In the following example toURI is a method with no arguments that returns a String. The function of this method reference takes a File (the object) and returns a String:

Reference to a constructor

Constructors are references using its type and “new”:

Here the constructor of StringBuffer with String parameter is referenced. Return type is the type of the constructor, parameters of the function are the parameters of the constructors.

 

 

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