import java.util.ArrayList;

interface MathOperation {
    public double compute(double a, double b);
}
class AdditionOperation implements MathOperation {

    public double compute(double a, double b){
        return a + b;
    }

}
//class SubtractionOperation implements MathOperation {
    //public double compute(double a, double b){
	//return a - b;
	//}
    //}

public class CalculatorApp {

    public static MathOperation add() {
    // TODO: Define a class named AdditionOperation that implements
    // MathOperation within this java source file, and outside of this
    // CalculatorApp class definition.  Note that this class definition
    // cannot be public because it is not being defined inside a file
    // that matches this class name.  The compute method in this class
    // should be defined to return the sum (first adds second)
    // of it's operands.  On the line below, return an instance of this
    // class from this method (instead of returning null).
	return new AdditionOperation();
    }

    public static MathOperation sub() {
    // TODO:  Return a new instance (instead of the null below) of an
    // anonymous class that implements MathOperation and defines its
    // compute method to return the difference (first minus second) of its operands. 
	return new MathOperation() {
	    @Override
	    public double compute(double a, double b){
		return a-b;
	    }
	};
    }

    public static MathOperation compare() {
    // TODO: Use a lambda expression on the line below to create and
    // return (instead of the null below) an object with a compute method
    // that returns 1 if the first operand is greater than or equals to the
    // second operand plus two and returns 0 otherwise
	return (a,b) -> (a>=b + 2) ? 1: 0;
    }

    /**
     * DO NOT MAKE ANY CHANGES TO THE MAIN METHOD BELOW FOR THIS ACTIVITY.
     * 
     * This main method uses the objects returned by the methods above to
     * display the sum, difference, and product of operands between 1 and 5.
     * @param args is not used by this program
     */
    public static void main(String[] args) {
        // add all math operations to this array
        ArrayList<MathOperation> ops = new ArrayList<>();
        ops.add( add() );
        ops.add( sub() );
        ops.add( compare() );

        // display table of math operations applied to operands
        System.out.println("Operands:  add  sub  cmp");
        for(int b = 1; b < 6; b++) // second operand (b) goes from 1 to 5
            for(int a = b; a < 6; a++) { // first operand from b to 5
                System.out.print("     "+a+","+b+":"); // print operands first
                for(MathOperation op: ops)
                    if(op != null) // then print out result of operation
                        System.out.printf( "%5.1f", op.compute(a,b) );
                    else // or a dash when the operation is null
                        System.out.print("    -");
                System.out.println(); // print each operand pair on a new line
            }
    }
}