Introduction to Computer Science Unit 4B. Programs: Classes and Objects

Transcription

1 Introduction to Computer Science Unit 4B. Programs: Classes and Objects This section must be updated to work with repl.it 1. Copy the Box class and compile it. But you won t be able to run it because it does not have a main method. Create a second class file named TestBoxes which has a main method. In the main method do the following: - create a Box object 2 ft wide by 6 ft long - call the getarea method and display the result - call the bigger method and double the dimensions of the box - call the getperimeter method and display the result public class Box { private double length, width; public Box( double len, double wid ) { length = len; width = wid; public double getarea() { return length * width; public double getperimeter () { double p = 2.0*( length + width); return p; 2. Copy the DiceRunner class and complete the Dice class. Compile and run. Set a breakpoint to check if the doubles method works correctly. public class DiceRunner { public static void main(string[] args) { Dice d = new Dice(); d.roll(); int n = d.gettotal(); System.out.println( n ); if ( d.doubles() ) System.out.println( "Yes" ); d.roll(); n = d.gettotal(); System.out.println( n ); public void bigger( double f ){ length = f * length; width = f * width; public class Dice { private int die1, die2; public Dice() { die1 = 0; die2 = 0; public void roll() { Assign die1 a random integer value between 1 and 6. Do the same thing for die2. Use Math.random(). public int gettotal() { return the sum of die1 and die2

2 if ( d.doubles() ) System.out.println( "Yes" ); public boolean doubles() { return true if both die are the same; otherwise return false. 3. Write another class (with a main method) in the same location as the files you created for Problem 2. In this main method, create one Dice object and roll the dice 100 times (in other words, call the roll method followed by the gettotal method 100 times). Count how many times you roll a 7 or 11. Also count how many times you rolled a 2, 3, or 12. And count how many doubles you got. Display the results as percents. For example: You rolled a 7 or 11 21% of the time. You rolled a 2, 3, or 12 13% of the time. You rolled doubles 15% of the time Note. Take advantage of the fact that you are rolling the dice 100 times to calculate the percentages 4. Copy the Circle class and complete the two methods to the right. getc should return the circumference of the circle and changer should assign the value of the parameter to the radius. Write a second class with a main method. In the main method: - create a Circle object with a radius of 3. - call the getc method and display the returned value (it should be ) - call the getarea method and display the returned value (it should be ) - call the changer method and change the circle s radius to 1. - call the getarea method again and display the returned value (it should 5. Write the Employee class so that when the main method in RunEmployee is executed, the following is displayed. Salary is Salary is Salary is public class Circle { private double radius; public Circle( double r ) { radius = r; public double getarea() { double a = Math.PI * radius * radius; return a; public double getc () { it returns the circle s circumference public void changer( double r ) { changes the value of radius to r public class RunEmployee { public static void main(string[] args) { Employee e = new Employee( ); e.increase( ); double p = e.getpay(); System.out.println( "Salary is " + p ); e.increase( );

3 The Employee class has one instance variable for storing an Employee s salary. p = e.getpay(); System.out.println( "Salary is " + p ); Note: the increase method should change the value of the instance variable. The getpay method simply returns the value of the instance variable. e.increase( ); p = e.getpay(); System.out.println( "Salary is " + p ); 6. Finish the Travel class. Then write a second class that has a main method. In the main method: - Write a loop that iterates 21 times with the counter going from 6 to 40 in steps of two. - In the body of the loop, create a Travel object and call each method. Print the returned values. - The output should look like this: people = 6, vans = 1, canoes = 2, planes = 1 people = 8, vans = 1, canoes = 3, planes = 1 people = 10, vans = 2, canoes = 4, planes = 1 people = 12, vans = 2, canoes = 4, planes = 1 people = 14, vans = 2, canoes = 5, planes = 2... people = 32, vans = 4, canoes = 11, planes = 3 people = 34, vans = 5, canoes = 12, planes = 3 people = 36, vans = 5, canoes = 12, planes = 3 people = 38, vans = 5, canoes = 13, planes = 4 people = 40, vans = 5, canoes = 14, planes = 4 7. The Prism class represents a rectangular prism. Complete the two methods. 8. Write another class that has a main method. In the main method: -Create a Scanner object and have the user enter three integers. - Instantiate a Prism object using those three integers. - Call the surfacearea method and print the returned value. - Call the issmall method. If it returns true, print This is a small prism. If the method returns false, print This is not a small prism. Here is sample output. public class Travel { private int people; public Travel( int n ) { people = n; public int gobyvan(){ this returns the number of vans required to transport everyone (8 per van) public int gobycanoe(){ this returns the number of canoes required (3 per canoe) public int gobyplane() { this returns the number of planes required (12 per plane) public class Prism{ private int len, w, h; public Prism( int a, int b, int c ) { len = a; w = b; h = c; public int surfacearea(){ Calculates and returns the surface area of the prism. public boolean issmall(){

4 Enter the length, width, height Its surface area is 94 square units This is a small prism 9. Copy the Car class. In another class s main method, create two car objects. Write a while loop where the drive method is called for each car and their locations are printed. When a car has gone over 200 miles, the loop stops and that car is the winner. Here is one sample output. Car 1: 4 miles, Car 2: 36 miles. Car 1: 14 miles, Car 2: 71 miles. Car 1: 17 miles, Car 2: 75 miles. Car 1: 156 miles, Car 2: 178 miles. Car 1: 167 miles, Car 2: 217 miles. Car 2 wins But obviously sometimes Car 1 will win and there could even be a tie. 10. First complete the Number class. Then we play the guessing game. Each turn the user gets to ask if the secret number is a multiple of some number and then they get to guess the secret number. Here's a rough outline. public class Runner { public static void main(string[] args) { create a Scanner object create a Number object boolean keepplaying = true; int count = 0; while ( keepplaying ) { count++; Ask the user to enter a positive integer. Get response and call the multipleof method. Print a message that indicates if the secret number is a multiple of that input or not Ask the user to guess what the secret number is. Call the guess method. If the user s right then print Congratulations, print count, and set keepplaying to false (to get out of the loop). If the user is wrong, then indicate that. Calculates the volume of the prism. If the volume is less than 75 cubic units, then this is a small prism and the method returns true. Otherwise the method returns false. public class Car { private int x; // location of the car public Car( ) { x = 0; public int getx(){ return x; public void drive() { x= x + (int)( 40*Math.random()); public class Number { private int num; public Number( ) { num = (int)(100*math.random() )+1; public boolean multipleof( int x ){ returns true if num is a multiple of x public boolean guess( int x ) { returns true if num equals x; otherwise it returns false Enter an integer: 2 The number is NOT a multiple of 2 Guess the secret number: 13 That s not it. Enter an integer: 3 The number is a multiple of 3

5 Guess the secret number: 3 That s not it. To the right is one possible outcome (though it will probably take more than 3 tries to guess the number). Enter an integer:5 The number is a multiple of 5 Guess the secret number: 45 You to it in 3 tries. 11. The Line class objects represent simple linear equations that can be written in slope-intercept form. Complete the two methods of the Line class. 12. Write another class that has a main method. In the main method, create a Scanner object and write a loop that repeats five times. In the loop: Create a random slope (using Math.random) that is one of the following values: -3.0, -2.5, -2.0, , 3.0 If you get stuck on this, the code is below*. Create a random y-intercept that is an integer between -3 and +3. Create a Line object using the random slope and y-intercept. Call the display method. Generate a random x value between 0 and 10. Call the gety method and use this random value. Display the x and y values. Have the user enter x and y values. Call the issolution method to check if those values are a solution to the linear equation or not. Display an appropriate message. Print a blank line. * Here is one way to generate the random decimal values for the slope. int num = (int) (13*Math.random() ) - 6; double slope = 0.5 * num; public class Line{ public double slope, intercept; public Line( double m, double b ){ slope = m; intercept = b; public void display(){ if ( slope == 0 ) SOP( "y = " + intercept ); else if ( intercept < 0 ) SOP("y = " + slope +"x " +intercept); else if ( intercept == 0 ) SOP( "y = " + slope + "x" ); else SOP("y = " + slope + "x +" + intercept); public double gety( double x ){ Given a value for x, return the corresponding value for y public boolean issolution(double x, double y ){ Returns true if the parameters are a solution of the Line. Otherwise it returns false. Your solution may sometimes return false when it should return true due to small errors that can arise working with doubles. Ignore this problem or ask me how to solve it. Here s some sample output for this problem. y = -2.0x If x is 8.0, then y is Check if a point is a solution. Enter x then y (-1.5, 4.0 ) is a solution to this equation

6 y = 1.0x -2.0 If x is 1.0, then y is -1.0 Check if a point is a solution. Enter x then y (0.0, 2.5) is NOT a solution to this equation y = -1.0x -2.0 If x is 7.0, then y is -9.0 Check if a point is a solution. Enter x then y (7.0, -9.0) is a solution to this equation 13. Complete the move method of the GamePiece class. 14. Write another class that has a main method. In the main method, create two GamePiece objects. Keep calling the move method for each object until one of the two objects gets to 21. The output should look something like this: Player 1 has 4, Player 2 has 2 Player 1 has 8, Player 2 has 6 Player 1 has 9, Player 2 has 11 Player 1 has 16, Player 2 has 17 Player 1 has 17, Player 2 has 20 Player 1 has 18, Player 2 has 5 Player 1 has 3, Player 2 has 9 Player 1 has 8, Player 2 has 10 Player 1 has 12, Player 2 has 16 Player 1 has 14, Player 2 has 19 Player 1 has 16, Player 2 has 1 Player 1 has 21, Player 2 has 3 Player 1 wins public class GamePiece{ private int number; public GamePiece(){ number = 0; public void move(){ If number is 21, then do nothing. Otherwise, generate a random integer between 1 and 7 and add this to the instance variable. However, the instance variable should never have a value greater than 21. If it is 22, then reduce it to 1. If it is 23, then it becomes 2, and so on. public int getnumber(){ return number;