JAVA CERTIFICATION QUESTION: Functional interfaces and ...

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JAVA CERTIFICATION QUESTION: Functional interfaces and lambdas expressions

· java

Given:

interface Calculable {
  int change(int i);

  default int change(long l){
    return (int) l * 3;
  }
}

class Test {
  public static void main(String[] args){
    Calculable calculable = l -> l * 2; // Line 1
     System.out.println(calculable.change(1)); // Line 2
  }
}

What is the given program's output?

A. 1

B. 2

C. 3

D. Compilation fails on line 1

E. Compilation fails on line 2

Default methods

Answer👇👇👇

·ꓭ uoᴉʇdo sᴉ ɹǝʍsuɐ ʇɔǝɹɹoɔ ǝɥꓕ

The Calculable interface has only one abstract method, hence it's a functional interface.

The lambda expression used on line 1 represents that abstract method - it has nothing to do with the default method in the same interface.

That lambda expression doubles its argument.

Therefore, when number 1 is passed to the change method on line 2, number 2 is returned and printed out.