What is the purpose of a static method in interface from Java 8?

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Why are static methods supported from Java 8? What is the difference between the two lines in main method in below code?

package sample;
public class A {
    public static void doSomething()
    {
        System.out.println("Make A do something!");
    }
}

public interface I {
    public static void doSomething()
    {
        System.out.println("Make I do something!");
    }
}

public class B {
    public static void main(String[] args) {
        A.doSomething(); //difference between this
        I.doSomething(); //and this
    }
}

As we can see above, I is not even implemented in B. What purpose would it serve to have a static method in an interface when we can write the same static method in another class and call it? Was it introduced for any other purpose than modularity. And by modularity, I mean the following:

public interface Singable {
    public void sing();
    public static String getDefaultScale()
    {
        return "A minor";
    }
}

Just to put like methods together.

Answer

In the past, if you had an interface Foo and wanted to group interface-related utils or factory methods, you would need to create a separate utils class FooUtils and store everything there.

Those classes would not have anything in common other than the name, and additionally, the utils class would need to be made final and have a private constructor to forbid unwanted usage.

Now, thanks to the interface static methods, you can keep everything in one place without creating any additional classes.

It’s also important to not forget all good practices and not throw everything mindlessly to one interface class – as pointed out in this answer



Source: stackoverflow