Java 8 reduce method calls depending on a value-CodePudding

How to optimize method that returns the first non empty value returned of the checkN() methods and prevent the rest method calls and isEmpty() calls:

private String validate() {
    String message = check1();

    if (message.isEmpty()) {
        message = check2();
    }

    if (message.isEmpty()) {
        message = check3();
    }

    // total 5  checks been called

    return message;
}

#1 I thought of using stream filter and return first that has value, but it requires to call each check:

return Stream.of(check1(), check2(), check3(), ...).filter(message -> !message.isEmpty()).findFirst().orElse("");

CodePudding user response：

Instead of constructing a Stream of Strings, you can do a Stream of Supplier<String>, which would defer the invocation of the method until the filter needs to be checked in the stream pipeline:

return Stream.<Supplier<String>>of(this::check1, this::check2, this::check3, ...)
            .filter(check -> !check.get().isEmpty())
            .findFirst()
            .map(Supplier::get)
            .orElse("");

A better variant is to do the mapping from Supplier to the result String before the filter (the advantage is that this won't call the method with the non-empty result twice):

return Stream.<Supplier<String>>of(this::check1, this::check2, this::check3, ...)
            .map(Supplier::get)
            .filter(message -> !message.isEmpty())
            .findFirst()
            .orElse("");

CodePudding user response：

You said you thought of stream filter first but a stream is not really required in this case.

creating a list of suppliers is the clearly the right approach
but you need to reverse the test condition and return if true (i.e. the message is not empty).
just continue to call the methods until the test succeeds and returns the message.

List<Supplier<String>> checkList = List.of(this::check1,
        this::check2, this::check3, this::check4, this::check5);

    
private String validate() {
    String message;
    for (Supplier<String> nextCheck : checkList) {
        if (!(message = nextCheck.get()).isEmpty()) {
            return message;
        }
    }
    return "";
}

Note that you could have achieved the same optimization using your initial approach but changing the condition.

public String validiate() {
    String message;
    if (!(message = check1()).isEmpty()) {
        return message;
    }
    if (!(message = check2()).isEmpty()) {
        return message;
    }
    if (!(message = check3()).isEmpty()) {
        return message;
    }
    
    // other message checks
    
    return "";
}