operator interface in Java

Unary Operator and Binary Operator are also two functional interfaces. They both extend the Function and BiFunction, respectively. Unary Operator extends Function, and Binary Operator extends Bi-Function. 
```
import java.util.function.*;
  
public class Main {
    public static void main(String args[]) {
        UnaryOperator<Boolean> op = UnaryOperator.identity();
        System.out.println(op.apply(true));
        
        BinaryOperator<Integer> op2 = BinaryOperator.maxBy(
                         (a, b) -> (a > b) ? 1 : ((a == b) ? 0 : -1));
        System.out.println(op2.apply(98, 12));
    }
}
```
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