Introduction to Computer Science Exercises for Unit 4A: Classes and Objects 1. This compiles and runs. What is displayed?

Transcription

1 Introduction to Computer Science Exercises for Unit 4A: Classes and Objects 1. This compiles and runs. What is 2. This compiles and runs. What percent of the time will s be true? What percent of the time will t be true? System.out.println( 3 < 5 ); System.out.println( 66 / 10!= 61 / 10 ); boolean p = false; boolean q = true; System.out.println( p && q ); System.out.println( p q ); System.out.println( p!= q ); boolean r = true; System.out.println( r && p && q ); System.out.println( r p q ); boolean s = Math.random() < 0.5; boolean t = Math.random() < 5; 3. If the user enters 17, what will be Scanner s = new Scanner( System.in ); System.out.print( "Enter a positive integer " ); int x = s.nextint(); boolean e = x % 2 == 0; System.out.println( e ); 4. If H is printed, what is the value of x? boolean x; // x is assigned a value 5. What are the possible values of num? 6. If num is 1, what is printed? 7. What has to happen for count to be 8. Could the code print just this? If the program prints the following numbers, what is the last number to be printed? if ( x ) System.out.println( "H" ); else System.out.println( "K" ); int num = (int)( 2*Math.random() ) + 1; boolean boo = num >= 2; if ( boo ) System.out.println( "A" ); else System.out.println( "B" ); int count = 0; boolean game_over = false; while( game_over == false ){ int num = (int)( 6*Math.random() ); count++; System.out.print( num + " " ); if ( num == 4 ) game_over = true; System.out.println( count ); 1

2 10. What is 11. What is 12. What is 13. What is public class PointEx{ Point pt1 = new Point( 5, 8 ); Point pt2 = new Point( -4, 1 ); double yak = pt2.gety(); System.out.println( yak ); double xray = pt1.getx(); System.out.println( xray ); public class GoodPoint{ Point p = new Point( ); Point pp = new Point( 3, 4 ); double d = p.distance( 12, 5 ); System.out.println( d ); d = p.distance( pp ); System.out.println( d ); public class PointyHat{ Point a = new Point( 5, 7 ); Point b = new Point( 3, 4 ); b.translate( 2, 6 ); a.move( 14, 1 ); double n1 = b.gety(); double n2 = a.getx(); System.out.println( n1 + ", " + n2 ); boolean boo = a.equals( b ); System.out.println( boo ); public class PointyStick{ Point g = new Point( -2, 7 ); Point h = new Point( 9, 7 ); Point k = new Point( 8, 8 ); double dist = h.distance( g ); System.out.println( dist ); dist = h.distance( k ); System.out.println( dist ); 2

3 14. What is Code inside the main method Point p1 = new Point( -2, -5 ); Point p2 = new Point( 6, 0 ); Point p3 = new Point( 7, 12 ); double num = p2.getx(); num = p3.gety(); num = p1.getx(); 15. What is Code inside the main method Point here = new Point(); Point there = new Point( 4, 3 ); double num = here.distance( there ); num = there.distance( here ); there.translate( 0, -2 ); here.move( 5, 7 ); num = here.distance( there ); num = here.distance( 5, 7 ); 16. Why does the second line NOT compile? Point pt = new Point( 3, 10 ); pt.translate( 4 ); 17. Why does the second line NOT compile? Point spot = new Point( -3, 0 ); int w = spot.getx(); 18. Why does the second line NOT compile? Point x = new Point(); double num = x.move( 4, 8 ); 19. Create a Point object that has these coordinates -2, 5. Then call the translate method and move the Point 3 units to the right (but not up or down). Then call the getx method and display the returned value. 20. Create a Point object at the origin (in the simplest manner possible). The find and display the distance from that Point to ( 39, 73). 3

4 21. What coordinates does the user have to enter to get You win! to be printed? 22. If the user enters 3 for the x coordinate and 4 for the y coordinate, what will be printed at the end? 23. If the user enters 2 for the x coordinate and 1 for the y coordinate, what will be printed at the end? import java.util.scanner; Scanner scan = new Scanner( System.in ); System.out.print( "Enter an x coordinate " ); int xx = scan.nextint(); System.out.print( "Enter a y coordinate " ); int yy = scan.nextint(); Point p1 = new Point( xx, yy ); Point p2 = new Point(); if ( p1.equals( p2 ) ) System.out.println( "You win!" ); p2.move( 2, 1 ); double d = p1.distance( p2 ); d = d*d; System.out.println( d ); Note. The actual numbers being printed by differ from your answers by or so. 24. What is different import java.util.scanner; about how the numbers are entered? 25. What are possible coordinates of the p2? Scanner scan = new Scanner( System.in ); System.out.print( "Enter x and y coordinates " ); int x = scan.nextint(); int y = scan.nextint(); Point p1 = new Point( x, y ); 26. What has to happen for the user to win? 27. What is the minimum number of tries? What is the maximum if the person guesses whatever they want? int other_x = (int)(2*math.random()); int other_y = (int)(2*math.random()); Point p2 = new Point( other_x, other_y ); int count = 1; while ( p1.equals( p2 ) == false ){ System.out.println( "Wrong." ); System.out.print( "Enter x and y again " ); x = scan.nextint(); y = scan.nextint(); p1.move( x, y ); count++; System.out.println( "You win!" ); System.out.println( "It took " + count + " tries" ); 4

5 28. What is 29. What is 30. What is import java.awt.rectangle; Rectangle rachel = new Rectangle( 3, 4 ); double num = rachel.gety(); num = rachel.getwidth(); boolean a = rachel.contains( 2, 2 ); System.out.println( a ); a = rachel.contains( 5, 1 ); System.out.println( a ); rachel.setbounds( 6, -3, 2, 11 ); System.out.println( rachel.gety() ); import java.awt.rectangle; Rectangle rock = new Rectangle( 1, 2, 3, 4 ); double num = rock.getx(); num = rock.getheight(); rock.translate( 4, -1 ); num = rock.getx(); num = rock.getheight(); import java.awt.rectangle; Rectangle r = new Rectangle( 5, 5 ); r.setbounds( -1, 4, 2, 3 ); double num = r.gety(); num = r.getwidth(); r.translate( 3, 0 ); num = r.getwidth() * r.getheight(); num = r.getx(); 5

6 31. What is Code inside the main method Rectangle rudolph = new Rectangle( 4, 1, 4, 4 ); Rectangle becky = new Rectangle( 3, 2, 4, 4 ); boolean b = becky.equals( rudolph ); System.out.println( b ); becky.translate( 1, -1 ); b = becky.equals( rudolph ); System.out.println( b ); rudolph.setbounds( -1, 0, 6, 3 ); double x = becky.getx(); System.out.println( x ); x = rudolph.getx(); System.out.println( x ); 32. Why does the second line NOT compile? Rectangle re = new Rectangle( 6, 8 ); int w = re.getwidth(); 33. Why does the second line NOT compile? Rectangle ar = new Rectangle( 1,1,1,1 ); double k = ar.setbounds( 2,2,2,2 ); 34. Why does the second line NOT compile? Rectangle e = new Rectangle( 6, 3 ); double y = e.gety( 3 ); 35. Create a Rectangle object. Its left corner is at 7, 2. Its width is 5 and its height is 9. Call the contains method and display OK if the rectangle contains the point at (x1, y1) 36. Create a Rectangle with a width of 4 and a height of 8. Its corner should be at the origin. Call the translate method and shift the rectangle by h in the x direction and v in the y direction. 37. Create two Rectangle objects (you pick the locations and sizes). Then call the intersects method and display OK if they intersect. int x1 = (int)(10*math.random()); int y1 = (int)(10*math.random()); int h = (int)(10*math.random()); int v = (int)(10*math.random()); 6

7 38. To the right is the Cat class. In the space below, create a Cat object and feed it 2 ounces of food. Then find out its age and display it. 39. To the right is the Dog class. In the space below, create a 45 pound Dog. Then let it eat for 5 minutes. If it is a good dog, print YES. 40. To the right is the Snake class. In the space below, create a 20 inch Snake. If it is deadly, print RUN. If it is not deadly, print OK. Call the crawl method and have it crawl for 30 minutes. Display how far it travelled. Cat class Constructor Cat() Methods return type, name, parameters int age() returns age void feed( int n ) n = ounces of food Dog class Constructor Dog( double w ) w = weight in lbs Methods return type, name, parameters void eat( int m ) m = minutes boolean good() returns true if good Snake class Constructor Snake( int n ) n = length in inches Methods return type, name, parameters boolean deadly() returns true if poisonous double crawl(int m) m = minutes returns distance traveled in inches 7