java - CompletableFuture allof timeout handling

Question

The effect you want to achieve: If the future collection does not return within 3 seconds, the completed future will be extracted. Compilation error, "Cannot infer functional interface type."

世界只因有你 · Answer

The problem with the compilation error is that the subject did not pay too much attention. This can be easily checked.
You can see the red area of the error report, which is the second parameter of the applyToEither method. Then check it applyToEither Parameter format of method

public  CompletableFuture applyToEither(
        CompletionStage other, Function fn) {
        return orApplyStage(null, other, fn);
    }

The second parameter is a Function. What Function requires is to return a result based on a parameter. However, the question clearly states that there are no parameters. It is written as a Supplier. Of course, the parameter type is not Meet the requirements of method applyToEither