Lab week 5

Objectives

• Get familiar with data type, variable, expression, method, parameter list and return type

• Distinguish local variables from parameters

• Get familiar with Class and object

• Get familiar with Sequential Execution

Exercise 1 (3%) is marked on a scale from 0-3 marks.

• Question 1: 0.5 mark

• Question 2: 0.5 mark

• Question 3: 0.5 mark

• Question 4: 0.5 mark

• Question 5: 0.5 mark

• Question 6: 0.5 mark

Question 1 (0.5 mark) : 

The following program is for calculating the radius of a circle centred at the original according to the x coordinate and the y coordinate (x,y) of a point on the circumference.

The program asks the user to input the x coordinate and the y coordinate. Try the following example input, analyze the output and explain the reason of the output.

import java.util.*;

public class JavaApplication1 {

    public static void main(String [] args){

        double xCoordinate, yCoordinate, radius;//declare x, y, r as double

        Scanner keyboard = new Scanner(System.in);//get input from keyboard System.out.print("Enter x: ");

        xCoordinate = keyboard.nextDouble();//input x

        System.out.print("Enter y: ");

        yCoordinate = keyboard.nextDouble();//input y

        radius = Math.sqrt(Math.pow(xCoordinate,2) + Math.pow(yCoordinate,2));//compute r = (x^2+y^2)^0.5

        System.out.printf("Radius = %.2f\n", radius);//output radius with 2 decimal point precision System.out.print("Enter remainingDouble: ");

        double remainingDouble = keyboard.nextDouble();//input remainingDouble, when did we input it?

        System.out.printf("remainingDouble = %f\n", remainingDouble);//output

    }

}

Example of the program output (the text in bold indicates the user input):

Enter x: 3

Enter y: 4 10

Radius = 5.00

Enter remainingDouble: remainingDouble = 10.000000

Question 2 (0.5 mark) : 

Write a class to compute the property cost according to the following UML diagram and expressions. The area of a property is obtained from the command line arguments.

Expresssions required in method double calcTotalCharges(double) are as follows:

actualArea = area * RATE

propertyCharge = actualArea * UNITPRICE

propertyCost = propertyCharge + propertyCharge * GST

Input the command line argument: 155.67

Example of the program output:

Property cost: 263.70

Question 3 (0.5 mark) : 

Analyze, compile and fix bugs in the following program so that the modified program will have the output in the example:

public class CircleBugs {

    public static void main(String[] args) { 

        double t = Double.parseDouble(args[0]); int r = Integer.parseInt(args[0]);

        System.out.println("r = " + r + ", t = " + t) double c = 2 * Math.PI * r;

        double A = Math.PI * r * r; double x = r * cos(t); double y = r * sin(t);

        System.out.println("c = " + c ); System.out.println("A = " + A ); System.out.println("x = " + x + ", " + "y = " + y );

    }

}

Input the command line argument: 1.2 0.6

Example of the program output:

r = 1.2, t = 0.6

c = 7.5398223686155035

a = 4.523893421169302

x = 0.9904027378916139, y = 0.6775709680740424

Question 4 (0.5 mark) : 

Draw the workflow of calcTotalCharges() method and main() method in Question

2. See diagrams of Sequential Execution in lecture notes.

Question 5 (0.5 mark) : 

Implement a program that:

- Prompts the user to enter a floating point number nA

- Calculates nB = nA^2.1

- Displays nB with 1 decimal point precision if it is less than 129.0, otherwise it displays a constant value 129.0

Question 6 (0.5 mark) : 

Implement a program that:

- Reads a floating-point number nA from the command line

- Calculates nB = e^nA where e is the base of natural exponential function

- Coverts nB to an integer number discarding its decimal part

- Displays nB

This assignment has been answered 4 times in private sessions.