Why isn't it necessary to assign a method's return value to a variable? [duplicate]

Answer 1

You can annotate a method with @CheckReturnValue if its return value should always be used. Static code analysis like FindBugs consider this annotation and raise warning when you violate it.

At least this is very reasonable when the method returns some kind of object that needs final processing at the end where the caller is responsible for. This is true for resources that must be closed at the end. Locks that must be released at the end ...

Answer 2

In java functions are not pure, so they may be run for the side effects only. It's just in this case there are no side effects... Consider

public String show() {
    System.out.println("Hello");
    return "Hello";
}

Now would you want a warning? The compiler can't know if you were running it for the side effect or the value, so why insist?

Answer 3

This is the design of the language.

In many cases, methods returns a value you don't care about. For example StringBuilder.append() returns the object itself.

It is true that in some cases an important return value might be lost. For example, InputStream.skip(long n) returns the number of bytes skipped. And read returns the number of bytes read. There are some tools (Checkstyle, FindBugs) that detect such bugs. But the language itself doesn't request checking the return value. And even if it did, the program could choose to ignore the value.

Answer 4

Because you don't necessarily need the returned value.