ExpressionOverBlockLambda
Since Checkstyle 14.1.0
Description
Checks that expression lambdas are used instead of single-line block lambdas where possible.
Rationale: According to the OpenJDK Java Style Guidelines (and general modern Java conventions), expression lambdas are preferred over single-line block lambdas for readability and conciseness.
A single-line block lambda is a lambda whose body is a block ({...}) that fits on a single line and contains only one statement that could be written as an expression lambda.
Examples
To configure the check:
<module name="Checker">
<module name="TreeWalker">
<module name="ExpressionOverBlockLambda"/>
</module>
</module>
Example:
public class Example1 {
public void foo() {
// violation below 'preferred over single-line'
Runnable a = () -> { System.out.println("hello"); };
// violation below 'preferred over single-line'
Function<Integer, Integer> b = x -> { return x + 1; };
// ok - expression lambda
Runnable c = () -> System.out.println("hello");
// ok - multi-line block lambda
Runnable d = () -> {
System.out.println("hello");
};
// ok - void return
Runnable e = () -> { return; };
// ok - multi-statement block
Runnable f = () -> {
System.out.println("hello");
System.out.println("world");
};
}
}
Example of Usage
Violation Messages
All messages can be customized if the default message doesn't suit you. Please see the documentation to learn how to.
Fully Qualified Name
com.puppycrawl.tools.checkstyle.checks.coding.ExpressionOverBlockLambdaCheck
Use this fully qualified class name in configuration when an exact class reference is required.