Java functional programming

what do you mean by functional? it is an interface that contains only one abstract method.

what is predicate ? predicates mean functions with one argument that return a boolean value

consider an example:

@FunctionalInterface
public interface EvenOdd {
    
    Boolean isEven(int number);
    // rest can be only complete methods
}

in this there is only one method hence that is an potential predicate.

The above defined predicate can be used in the following manner:

public class StreamOne
 {
    public static void main(String[] args) {
        EvenOdd evenOdd = num-> num%2==0; //Here we have provided the implementation for that predicate.
        System.out.println("\n\n");
        System.out.println(evenOdd.isEven(20));
        System.out.println(evenOdd.isEven(21));
    }
}

for simpler understanding, we could consider the example as:

public boolean isEven(int num){

    Boolean val = num%2==0;
    return val;
}

if we look carefully the compiler already knows that:

• method is alway public as this is from an interface
• compiler knows that it has a boolean return type, as there is only one method to look at.
• compiler knows the method name, as there is only one method to look at.

so we can omit all that info to

(num)->{
    Boolean val = num%2==0;
    return val;
}

and now because it has only one argument, we can get away with the bracket

num->{
    Boolean val = num%2==0;
    return val;
}

if we can make the method body to one liner then we can even remove the curly braces.

num -> num%2==0;

That is how we got this predicate.

Java provided functional interfaces