Task 1: Print a series of random integers between 0 and 99 until the value 77 is printed. Use the Random class to generate random numbers.

Transcription

1 Task 1: Print a series of random integers between 0 and 99 until the value 77 is printed. Use the Random class to generate random numbers. Task 2: Print a series of random integers between 50 and 99 until the sum of the last two random numbers is 77. Task 3: Print a series of 50 random integers between 0 and 999. Return the largest random integer in the series. Page 1 of 7

2 Task 1: Print a series of random integers between 0 and 99 until the value 77 is printed. Use the Random class to generate random numbers. Include the following in your program: import java.util.random; Analysis of the task: Loop condition: Termination condition: value == 77 Local variables needed: public static void printrandomintegers () Random source; int rvalue; source = new Random(); rvalue = source.nextint(100); while ( ) System.out.print (rvalue + ); // terminate with the following condition: System.out.println ( ); Page 2 of 7

3 Task 2: Print a series of random integers between 50 and 99 until the sum of the last two random numbers is 77. An example of output: Seven Eleven is Seventy Seven Analysis: Loop condition: Termination condition: Local variables needed: rval1, rval2, public static void seventyseven () Random source; source = new Random(); int rval1, rval2; rval1 = rval2 = while ( ) Page 3 of 7

4 Task 3: Print a series of 50 random integers between 0 and 999. Return the largest random integer in the series. Analysis: Loop condition: Termination condition: Local variables needed: public static int identifythelargestfromrandomseries () Random source; source = new Random(); return ; How to stop infinite loop in BlueJ: When your program is running, the Work Indicator Bar (shown below) will turn red. To stop the current program (without quitting BlueJ), right click on the bar and select Reset-Machine or press Ctrl-Shift-R. Work Indicator Bar Page 4 of 7

5 Complete the odd numbered problems for in class group exercise. Complete the even numbered problems for homework. Read the specific instructions given at the bottom of the last page for writing the methods in BlueJ. 1. Given a method public int mistery (int n) int k; k = 1; while (k <= n) if (n % k == 0) k++; return k; Can the above method enter an infinite loop? What would be the return value of mistery(0)? What would be the return value of mistery(1)? What would be the return value of mistery(3)? 2. Given a method public void unknown (int n) while (n!= 1) System.out.print (n + ); if (n % 2 == 0) n = n / 2; else n = 3 * n + 1; System.out.println (n); The last println (after the loop) always print the same value, regardless the value of n passed to the method. What value is that? What would be the output of unknown(5)? What would be the output of unknown(7)? 3. Lift Off. Write a method that prints a count down from a given number to 1 then prints Lift Off. liftoff(5) prints the following two lines of output Lift Off liftoff(12) prints the following two lines of output Lift Off public static void liftoff (int begin) Page 5 of 7

6 4. Print the first N numbers in the Fibonacci sequence. printfibonacci (6) shall print printfibonacci (10) shall print public static void printfibonacci (int N) 5. Print a series of random integer between 0 and 9 but keep their sum below Print a series of random integer between 0 and 9, keep their sum as close as possible to 100 without exceeding Print a series of random integers between 0 and 99 until you see two consecutive random integers of the same value. 8. Given an integer, print all factors of that number starting from the smallest factor but smaller than the number itself. printfactors (11) shall print 1 printfactors (51) shall print printfactors (53) shall print 1 printfactors (60) shall print Use the modulo operator (%) to check for factors, for instance: 24 % 4 is 0 24 % 5 is 4 (5 is not a factor of 24) 24 % 6 is 0 24 % 7 is 3 (7 is not a factor of 24) public static void printfactors (int value) 9. Given an integer, determine whether the number is prime. isprime (11) returns true isprime (51) returns false isprime (53) returns true isprime (60) returns false public static boolean isprime (int valuetocheck) Page 6 of 7

7 10. Print a single month calendar with the first day falls on a given day of the week. For simplicity assume the month has only 30 days. For example: printcalendar (0) prints a calendar that begins on a Sunday Su Mo Tu We Th Fr Sa printcalendar (3) prints a calendar that begins on a Wednesday Su Mo Tu We Th Fr Sa public static void printcalendar (int firstweekday) You may be tempted to solve the problem using nested loop. However, this problem can be solved by using just a single loop. The nature of the solution is just to print numbers from1 to 30. To make these numbers resemble a monthly calendar, extra blank must be printed prior to the beginning of the month, and the text cursor has to be placed on the next line after a Saturday is printed. Hints: Use System.out.printf() to format each integer output to a desired width. Assume that the two integer variables hournow, and minnow have been initialized to 9 and 5, respectively. Printf replaces %d in the format string with the actual value of the data. The \n below is to place the text cursor on the new line. Java Statement System.out.printf ( Time is %d:%d am\n, hournow, minnow); System.out.printf ( Time is %2d:%2d am\n, hournow, minnow); System.out.printf ( Time is %02d:%02d am\n, hournow, minnow); System.out.printf ( Time is %d:%02d am\n, hournow, minnow); Output Time is 9:5 am Time is 9: 5 am Time is 09:05 am Time is 9:05 am Instructions for BlueJ 1. Create a new BlueJ project. Choose an appropriate name for the project 2. In the project, create a new class LoopExercise 3. In the class write the static methods as directed in each homework question above. 4. To test static methods, you don't have to create an instance of the class. The methods can be invoked directly from the class. To do this in BlueJ, right-click on the class and then select a static method that you want to test. Page 7 of 7