What are lambda expressions in Java?
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Overview
We use a lambda expression as an anonymous function to pass around a value in Java. Lambda expressions are often used in conjunction with functional interfaces, which are interfaces that contain only a single abstract method.
Functional interfaces can be found in the java.util.function package, and some of the more useful ones include the Predicate, Function, and Consumer interfaces.
Syntax
We write the lambda expressions in the following format:
(parameters) -> {body}
Parameters
We can have multiple parameters, but the parameters of the lambda expression are optional. We separate multiple parameters with commas.
The body of the lambda expression contains the code that will be executed when the lambda expression is invoked.
For example, consider the following lambda expression:
(int x, int y) -> x + y
This lambda expression takes in two parameters (
Example
To use a lambda expression with a functional interface, we can do as follows:
import java.util.function.*;public class Main {public static void main( String args[] ) {BiFunction<Integer, Integer, Integer> adder;adder = (x, y) -> x + y;int result = adder.apply(1, 2);System.out.println(result);}}
Explanation
- Line 5: We use the
BiFunctionfunctional interface from thejava.util.functionpackage. TheBiFunctioninterface is a generic interface that takes in three type parameters: the first two parameters are for specifying the type of the two input parameters, and the third parameter is for the type of the return value. In the above example, we're specifying that the first parameter is anInteger, the second parameter is anInteger, and the return value is also anInteger. - Line 6: It will invoke the lambda expression, passing in the values
1and2for thexandyparameters. The result of the lambda expression will be3, which is what will be stored in theresultvariable. - Line 8: We invoke the lambda expression by calling the
apply()method on theBiFunctionobjectadder.
As we can see, lambda expressions can be used to write code in a more concise and functional style.
