Statement lambda can be replaced with expression lambda

Question

I do user and invitation validation using the Optional facility

@DeleteMapping("/friends/{username}") public HttpEntity<Boolean> removeFriend( @ApiParam(value = "The user's name", required = true) @PathVariable String username ) { Long fromId = authorizationService.getUserId(); return userService.findByUsername(username) .map(user -> { return friendshipService.findFriendship(fromId, user.getId()) .map(friendship -> { friendshipService.removeFriendship(friendship); friendship.setToId(friendship.getFromId()); friendship.setFromId(friendship.getToId()); friendshipService.removeFriendship(friendship); return ResponseEntity.ok(true); }).orElseGet(() -> ResponseEntity.notFound().build()); }).orElseThrow(() -> new ResourceNotFoundException("User not found"));

However, IntelliJ is colouring my grey return, But when I remove the return, it highlights to me that there is no return.

Could someone explain how it works and what is it all about?

Seelenvirtuose · Accepted Answer · 2018-12-28 11:46:07Z

181

Your statement lambda

param -> { return expression; }

can be changed to an expression lambda:

param -> expression

Simple, isn't it? Note, that the curly brackets and the semicolon need to be removed.

edited Dec 28, 2018 at 11:46

answered Sep 15, 2017 at 11:46

Seelenvirtuose

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3 Comments

sdfsd Over a year ago

Works. Thanks. Which in your opinion is a better way to lambda this pastebin.com/imEtjwHp or this pastebin.com/gcaUMYQ4?

Seelenvirtuose Over a year ago

There is no better in this context. Do it as you like. But for me, both code snippets are not readable. This should always be the first criterion for coding.

mochadwi Over a year ago

@Seelenvirtuose would you mind giving us an example for the readable code snippets?

MatPag · Accepted Answer · 2018-11-21 22:20:29Z

Sometimes I found useful to leave the braces where they are if the block of code is long enough (I think it improves readability)

In Android Studio you can locally disable the warning using //noinspection CodeBlock2Expr at the start of the method like in the example below

//noinspection CodeBlock2Expr button.setOnClickListener((View v) -> { //a long single method call... });

Nachiket Doke · Accepted Answer · 2020-12-30 13:46:40Z

The Statement lambda can be replaced with expression lambda message appears when we use curly braces "{}" and semicolons ";" in expression lambdas for implementing functional interfaces. We can do away with those in such a situation. That being said, I personally feel it is a good coding practice to use block lambdas even for single line functional interface implementations, the way we do it for single line for and while loops.

Kishan Thakkar · Accepted Answer · 2023-03-14 12:51:27Z

Reports lambda expressions with code block bodies when expression-style bodies can be used instead. The result of the conversion is shorter and more clear.

Example:

Comparable<String> c = o -> {return 0;};

After the quick-fix is applied:

Comparable<String> c = o -> 0;

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