Function Interface in Java 8 with examples

This entry is part 31 of 43 in the series Java 8 Functional Interfaces

Function Interface is a part of the java.util.function package which is introduced in Java 8. It is an in-built Functional Interface. This function expect one argument as an input and produces a result. As it is a functional interface, it can be used assignment target for lambda expression or method reference. In this post, we are going to see several implementations of Function Interface by using different examples.

Function_Interface_Java8_Techndeck

 

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Look at Function Javadoc description below:

Function_Signature_Java8_Techndeck

 

 

 

 

Function Interface contains 4 methods:

  1. apply

  2. compose

  3. andThen

  4. identity

 

Let’s discuss these methods:

apply 

This method performs operation on the given argument and return the function result.

compose

This method returns a composed function that first applies the before function to its input, and then applies this function to the result. If evaluation of either function throws an exception, it is relayed to the caller of the composed function.

andThen

This method returns a composed function that first applies this function to its input, and then applies the after function to the result. If evaluation of either function throws an exception, it is relayed to the caller of the composed function.

identity

This method returns a function that always returns its input argument.

 

Lets understand above mentioned methods thorough various examples:

Example 1. ‘apply’ method

 

Example 2. ‘andThen’ & ‘compose’ methods

 

Java 8 Function Interface is an absolute useful addition as part of ‘Functional Interfaces’ and can serve variety of purposes. It is quite powerful as it can be used as a higher order functions through lambda functions and above examples could help you to get better idea on how to implement it.

 

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