CODEWITHSUNDEEP
javalambdajava-8
zizhuo64062kw
zizhuo64062kw

Reputation: 421

Java: how to pass Class to lambda

I try to make create multi dirs and files more easier with follwoing code:

package ro.ex;

class File {

    public interface Lamb {
        public void call(Class c);
    }

    public static void tap(Lamb l) {
        l.call(File.class);
    }

    public static void mkdir(String path) {
    }

    public static void main(String[] args) {
        File.tap((f) -> {
            f.mkdir("dir");
            f.mkdir("dir2");
        });
    }
}

but in f.mkdir("dir"), intellij idea raise can't resolve method 'mkdir'

my question is: how to change code to make code in main block work well

Upvotes: 0

Views: 140

Answers (2)

Konstantin Yovkov
Konstantin Yovkov

Reputation: 62864

According to the method contract, File.tap() accepts a Lamb parameter.

Lamb is a functional interface (contains only one abstract method) and the body of your lambda is the anonymous implementation of its abstract method.

The abstract method has a definition public void call(Class c) and this is why your code fails to compile. You're trying to pass a File object, instead of a Class one.

In the mean time, mkdir is a static method and can be invoked like this:

public static void main(String[] args) {
    File.tap((f) -> {
        File.mkdir("dir");
        File.mkdir("dir2");
    });
}

Upvotes: 3

Seelenvirtuose
Seelenvirtuose

Reputation: 20618

You defined a (functional) interface Lamb whose single method takes a Class as an argument.

So the f in your lambda expression (f) -> { ... } is of type Class. But this class does not know the method mkdir.

You have a static method mkdir in your custom class File. Static methods are called like this:

File.tap((f) -> {
    File.mkdir("dir");
    File.mkdir("dir2");
});

This makes the Class argument in method Lamb.call(Class) rather useless. Maybe you want to reconsider the design.

Upvotes: 1

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