Java Programming. Final Examination on December 13, 2015 Fall 2015

Transcription

1 Java Programming Final Examination on December 13, 2015 Fall 2015 Department of Computer Science and Information Engineering National Taiwan University Problem 1 (10 points) Multiple choice questions. Each is worth 1 points. 1. Which of the following reserved words in Java is used to create an instance of a class? (a) class (b) public (c) import (d) new. 2. Given 1 double x = 5, y = 2 ; What is the value of m after the following statement is executed? 1 i n t m = ( i n t ) ( x + y + x / y x * y x / (10 * y ) ) ; (a) 1 (b) 0.75 (c) 0.5 (d) 0 (e) Object-oriented programming allows you to derive new classes from existing ones. This is called (a) inheritance (b) abstraction (c) encapsulation (d) generalization. 4. Variables of a supertype can refer to a subtype object. This is called (a) inheritance (b) polymorphism (c) encapsulation (d) dynamic binding. 5. The visibility of Java modifiers increases in which of the following order: (a) private, package, protected, and public. (b) private, protected, package, and public. (c) package, private, protected, and public. (d) package, protected, private, and public. 6. Which of the following is the type of all Java exceptions? (a) RuntimeException (b) Exception (c) Error (d) Throwable. 7. Variables that are shared by every instances of a class are (a) class variables (b) public variables (c) instance variables (d) private variables. 8. Inside a static method of a class, we can use the keyword this. (T/F) 9. Similar to classes which can extend only one other class, an interface can extend only one other interface. (T/F) 1

2 10. All constant values defined in an interface are implicitly public, static, and final. (T/F) Problem 2 (20 points) Short questions. Each is worth 2 points except that Question 8 worth 6 points. Please give an example for each question. 1. Explain the difference between method overloading and method overriding. 2. Explain the difference between final, finally, and finalize? 3. What is this and super? 4. Explain the difference between static and instance members in one class. 5. Explain the difference between throw and throws? 6. Explain the difference between abstract classes and interfaces? 7. Let x be any input of some algorithm Γ(x), n = x be the input size, and f(n) be the growth rate of Γ(x). Suppose f(n) = 4n 3 100n By definition, there exists some g(n) such that f(n) O(g(n))). Note that g(n) are simple functions like n, n 2, and log n. Determine the degree of g(n) which is a tight bound for f(n). 8. Revisit the keywords we list in the very beginning of the class. Write down the keywords you don t know yet. Problem 3 (10 points) Write a program which estimates 3 by Monte Carlo simulation. It is clear that x is less than 3 if x 2 is less than 3. You may use Math.random() in the program. 2

3 ˆ Input - n: the number of random numbers ˆ Output - Approximate number for 3 Ans: 1 package javafinal ; 2 3 p u b l i c c l a s s montecarlosqrt5 { 4 p u b l i c s t a t i c void main ( String [ ] args ) { 5 i n t n = ( i n t ) 1 e6 ; 6 f o r ( i n t i = 1 ; i <= 1 0 ; i++) { 7 System. out. printf ( %7.6 f \n, ( new MonteCarloSimulator ( n ) ). getestimate ( ) ) ; 8 } 9 } 10 } c l a s s MonteCarloSimulator { 13 p r i v a t e i n t size = 0 ; 14 p r i v a t e double estimator = 0 ; MonteCarloSimulator ( i n t n ) { 17 size = n ; 18 f o r ( i n t i = 1 ; i <= n ; i++) { 19 generateonepath ( ) ; 20 } 21 } void generateonepath ( ) { 24 double x = 2 + Math. random ( ) ; 25 i f ( x * x < 5) { 26 estimator++; 27 } 28 } p u b l i c double getestimate ( ) { 31 r e t u r n 2 + estimator / size ; 32 } 33 } Problem 4 (10 points) Given a number x, and an integer n 0, write a program which produces x n by a recursive approach. For example, 3 4 = 3 (3 (3 (3))). ˆ Input - x R - n N {0} ˆ Output - x n 3

4 Ans: 1 package javafinal ; 2 3 p u b l i c c l a s s recursiveproblem { 4 p u b l i c s t a t i c void main ( String [ ] args ) { 5 System. out. println ( Product. recursivemethod ( 3, 4) ) ; 6 System. out. println ( Product. recursivemethod ( 3. 2, 4) ) ; 7 } 8 } 9 10 c l a s s Product { 11 s t a t i c i n t recursivemethod ( i n t x, i n t n ) { 12 i f ( n > 0) { 13 r e t u r n x * recursivemethod ( x, n 1) ; 14 } e l s e { 15 r e t u r n 1 ; 16 } 17 } s t a t i c double recursivemethod ( double x, i n t n ) { 20 i f ( n > 0) { 21 r e t u r n x * recursivemethod ( x, n 1) ; 22 } e l s e { 23 r e t u r n 1 ; 24 } 25 } 26 } Problem 5 (10 points) Write a program for lottery tickets ( 樂透 ). The program draws a set of 6 distinct numbers from 1 to 49. Meanwhile, the user enters 6 distinct numbers. In the end, the program shows you how many numbers you guess right. ˆ Input - 6 distinct numbers ˆ Output - The lucky numbers - The chosen numbers - The correct numbers you have For example, 4

5 Ans: 1 import java. util. Scanner ; 2 3 p u b l i c c l a s s lotterymain { 4 s t a t i c boolean [ ] reg_table = new boolean [ 4 9 ] ; 5 s t a t i c boolean [ ] guess_table = new boolean [ 4 9 ] ; 6 7 p u b l i c s t a t i c void main ( String [ ] args ) { 8 i n t [ ] bingonum ; 9 randomsecretnumbers ( ) ; 10 System. out. println ( Welcome to Java251 Lottery Game. ) ; 11 inputnumbers ( ) ; 12 shownumbers ( guess_table ) ; 13 System. out. println ( The l o t t e r y numbers are ) ; 14 shownumbers ( reg_table ) ; 15 bingonum = checknumbers ( ) ; 16 System. out. printf ( You have c o r r e c t number ( s ) : ) ; 17 shownumbers ( bingonum ) ; 18 System. out. printf ( Bye. ) ; 19 } s t a t i c void randomsecretnumbers ( ) { 22 i n t cnt = 0 ; 23 w h i l e ( cnt < 6) { 24 i n t tmp = ( i n t ) ( Math. random ( ) *10000 % 49) ; 25 i f ( reg_table [ tmp ] == f a l s e ) 26 reg_table [ tmp ] = t r u e ; 27 e l s e 28 c o n t i n u e ; 29 cnt++; 30 } 31 } s t a t i c void shownumbers ( boolean [ ] x ) { 34 f o r ( i n t i = 0 ; i < x. length ; ++i ) { 35 i f ( x [ i ] ) 36 System. out. printf ( %3d, i + 1) ; 37 } 38 System. out. println ( ) ; 39 } 40 s t a t i c void shownumbers ( i n t [ ] x ) { 5

6 41 f o r ( i n t i = 0 ; i < x. length ; ++i ) { 42 i f ( x [ i ] > 0) 43 System. out. printf ( %3d, i + 1) ; 44 } 45 System. out. println ( ) ; 46 } s t a t i c void inputnumbers ( ) { 49 Scanner in = new Scanner ( System. in ) ; 50 i n t cnt = 0 ; 51 i n t input = 0 ; 52 System. out. println ( P l e a s e e n t e r your numbers. ) ; 53 w h i l e ( cnt < 6) { 54 System. out. printf ( [%d ] :, cnt + 1) ; 55 input = in. nextint ( ) ; 56 i f ( input > 49 input < 1) { 57 System. out. println ( Out o f range. Try again. ) ; 58 c o n t i n u e ; 59 } e l s e i f ( guess_table [ input 1 ] == t r u e ) { 60 System. out. println ( You ' ve a l r e a d y chosen t h i s number. Try again. ) ; 61 c o n t i n u e ; 62 } e l s e 63 guess_table [ input 1 ] = t r u e ; 64 cnt++; 65 } 66 in. close ( ) ; 67 } s t a t i c i n t [ ] checknumbers ( ) { 70 i n t [ ] bingo = new i n t [ 6 ] ; 71 i n t cnt = 0 ; 72 f o r ( i n t i = 0 ; i < reg_table. length ; ++i ) { 73 i f ( reg_table [ i ] && guess_table [ i ] ) 74 bingo [ cnt++] = i + 1 ; 75 } 76 r e t u r n bingo ; 77 } 78 } Problem 6 (10 points) Use Point class to define a new class Circle which has the following members: Creates two Circle objects: ˆ c 1 : center = (0, 0), radius = 3 6

7 ˆ c 2 : center = (3, 4), radius = 2 Write a program which determines if the two circles share two intersecting points. You may consider the following snippet: 1 p u b l i c c l a s s CircleMain { 2 p u b l i c s t a t i c void main ( String [ ] args ) { 3 Circle c1 = new Circle ( c1, new Point ( 0, 0), 3) ; 4 Circle c2 = new Circle ( c2, new Point ( 3, 4), 2) ; 5 input. close ( ) ; 6 showcircle ( c1 ) ; 7 showcircle ( c2 ) ; 8 System. out. println ( That c1 o v e r l a p s c2 i s + c1. isoverlap ( c2 ) +. ) ; 9 } s t a t i c void showcircle ( Circle c ) { 12 System. out. printf ( %s : (%.2 f, %.2 f ) with r = %.2 f, area = %.2 f, p e r i m e t e r = %.2 f \n, 13 c. getname ( ), 14 c. getcenter ( ). getx ( ), 15 c. getcenter ( ). gety ( ), 16 c. getradius ( ), 17 c. getarea ( ), 18 c. getperimeter ( ) ) ; 19 } 20 } The result looks like: 1 c1 : ( , ) with r = , area = , perimeter = c2 : ( , ) with r = , area = , perimeter = That c1 overlaps c2 is f a l s e. Ans: 1 c l a s s Circle { 2 p r i v a t e Point center ; 3 p r i v a t e double radius ; 4 p u b l i c String name ; 5 6 Circle ( String str, Point pt, double r ) { 7 name = str ; 8 center = pt ; 9 radius = r ; 10 } p u b l i c Point getcenter ( ) { 13 r e t u r n center ; 14 } p u b l i c double getradius ( ) { 17 r e t u r n radius ; 18 } p u b l i c double getarea ( ) { 21 r e t u r n Math. PI * Math. pow ( radius, 2) ; 22 } 7

8 23 24 p u b l i c double getperimeter ( ) { 25 r e t u r n 2 * Math. PI * radius ; 26 } p u b l i c double getdistancefrin ( Circle c ) { 29 r e t u r n center. getdistancefrom ( c. center ) ; 30 } p u b l i c boolean isoverlap ( Circle c ) { 33 r e t u r n c. getradius ( ) + radius > center. getdistancefrom ( c. center ) ; 34 } 35 } Problem 7 (10 points) Extract the member method getdistancefrom in Point class and put it in an interface metric. Also define a new class Point3D for a point in the 3D world. Their relationship can be organized as follows: Note that you should implement the function getdistancefrom in both classes. Use the following snippet to check if the classes are well-defined. In the test program, create two Point3D objects: (0, 0, 0) and (1, 2, 3). Then show the distance between these points. Besides, create an Object object which is not an object of Point3D. Try to calculate the distance. Yet, an exception occurs and is thrown by the function getdistancefrom. 1 p u b l i c c l a s s Point3Dtest { 2 p u b l i c s t a t i c void main ( String [ ] args ) { 3 Point3D p1 = new Point3D ( 0, 0, 0) ; 4 Point3D p2 = new Point3D ( 1, 2, 3) ; 5 Object p3 = new Object ( ) ; 6 t r y { 7 System. out. printf ( The d i s t a n c e between p1 and p2 i s %f. \ n, p1. getdistancefrom ( p2 ) ) ; 8 } catch ( Exception e ) { 9 System. out. println ( e. getmessage ( ) ) ; 10 } t r y { 8

9 13 System. out. printf ( The d i s t a n c e between p1 and p3 i s %f. \ n, p1. getdistancefrom ( p3 ) ) ; 14 } catch ( Exception e ) { 15 System. out. println ( e. getmessage ( ) ) ; 16 } 17 } 18 } Ans: 1 2 c l a s s Point { 3 p r o t e c t e d double x, y ; 4 5 Point ( i n t x, i n t y ) { 6 t h i s. x = x ; 7 t h i s. y = y ; 8 } 9 10 double getx ( ) { 11 r e t u r n x ; 12 } double gety ( ) { 15 r e t u r n y ; 16 } double getdistancefrom ( Point p ) { 19 r e t u r n Math. sqrt ( Math. pow ( t h i s. x p. x, 2) + Math. pow ( t h i s. y p. y, 2) ) ; 20 } 21 } i n t e r f a c e metric { 24 double getdistancefrom ( Object p ) throws Exception ; 25 } c l a s s Point3D extends Point implements metric { 28 p r i v a t e double z ; Point3D ( i n t x, i n t y, i n t z ) { 31 super ( x, y ) ; 32 t h i s. z = z ; 33 } double getz ( ) { 36 r e t u r n z ; 37 } p u b l i c double getdistancefrom ( Object obj ) throws Exception { 40 i f ( obj i n s t a n c e o f Point3D ) { 41 Point3D p = ( Point3D ) obj ; 42 r e t u r n Math. sqrt ( Math. pow ( t h i s. x p. x, 2) + Math. pow ( t h i s. y p. y, 2) + Math. pow ( t h i s. z p. z, 2) ) ; 43 } e l s e { 44 throw new Exception ( This i s not a Point3D o b j e c t. ) ; 45 } 46 } 47 } Problem 8 (20 points) Revisit the producer-and-consumer problem. In pp of 9

10 Ch9, the UseData2 object has at most 1 unit in the field data. Based on this, write a program to simulate the producer-and-consumer problem whose field data is at most 2 in the UseData2 object. For example, As a hint, you may modify the UseData2 class. To terminate the program, you may think about how to use exceptions to interrupt the main thread, which changes the flag, say, isrunning, from true to false (see the program in p. 24 of Ch9). Let s make the program run for 30 seconds. Ans: 1 p u b l i c c l a s s pcproblem { 2 3 p u b l i c s t a t i c void main ( String [ ] args ) { 4 UserData3 uc = new UserData3 ( ) ; 5 new Producer ( uc ) ; 6 new Consumer ( uc ) ; 7 } 8 9 } 10 c l a s s UserData3 { 11 p r i v a t e i n t data ; 12 long runtime = System. currenttimemillis ( ) ; 13 boolean time = t r u e ; 14 s y n c h r o n i z e d void setdata ( ) { 15 i f ( data < 2) { 16 data++; 17 System. out. printf ( P : +1 ( so data = %d ) \n, data ) ; 18 checktime ( ) ; 19 notify ( ) ; 20 } 21 e l s e t r y { 22 wait ( ) ; 23 } catch ( InterruptedException e ) {} 24 } 25 s y n c h r o n i z e d void getdata ( ) { 26 i f ( data > 0) { 27 data ; 28 System. out. printf ( C: 1 ( so data = %d ) \n, data ) ; 29 checktime ( ) ; 30 notify ( ) ; 31 } 32 e l s e t r y { 33 wait ( ) ; 10

11 34 } catch ( InterruptedException e ) {} 35 } 36 void checktime ( ) { 37 i f ( System. currenttimemillis ( ) runtime > 30000) { 38 time = f a l s e ; 39 } 40 } 41 } 42 c l a s s Consumer implements Runnable { 43 UserData3 UC ; 44 Consumer ( UserData3 UC ) { 45 t h i s. UC = UC ; 46 Thread t = new Thread ( t h i s ) ; 47 t. start ( ) ; 48 } 49 p u b l i c void run ( ) { 50 w h i l e ( UC. time ) { 51 UC. getdata ( ) ; 52 t r y { 53 Thread. sleep ( ( i n t ) ( Math. random ( ) * 1000) * 2) ; 54 } catch ( InterruptedException e ) {} 55 } 56 } 57 } 58 c l a s s Producer implements Runnable { 59 UserData3 UC ; 60 Producer ( UserData3 UC ) { 61 t h i s. UC = UC ; 62 Thread t = new Thread ( t h i s ) ; 63 t. start ( ) ; 64 } 65 p u b l i c void run ( ) { 66 w h i l e ( UC. time ) { 67 UC. setdata ( ) ; 68 t r y { 69 Thread. sleep ( ( i n t ) ( Math. random ( ) * 1000) * 2) ; 70 } catch ( InterruptedException e ) {} 71 } 72 } 73 } SUBMISSION 1. Pack source codes into a zip or rar file with your full name. 2. Send the zip/rar file to d @ntu.edu.tw. 3. If you have any suggestion for improving this class, feel free to leave your feedback in the . Congratulations!!! To start, you don t have to be good; to be good, you have to start. Slogan of NTU Toastmasters 11