The purpose of this assignment is to provide experience with Exception Handling and Concurrent Programming in Java

Exercise 1 [Points 50]

import java.io.*;

public class Sums {

    public static void sum(BufferedReader in){ 
        // takes a sequence of integeres in input, and outputs their sum

	int s, nextInt;
	s = 0;

	System.out.println("Please input the sequence of integers to sum, terminated by a 0");
        nextInt = Integer.parseInt(in.readLine());
                //Read next datum in input. An integer is expected

	while (nextInt!=0) {
	    s = s + nextInt;
	    nextInt = Integer.parseInt(in.readLine());
	}

        System.out.println("The sum is " + s);
    }

    public static void main(String[] arg) {         

	BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
                         //"in" will receive data from the standard input stream
	String c;
 
	System.out.println("Do you wish to calculate a sum? (y/n)");

	c = in.readLine();
         //Read next datum in input. A string "y" or "n" is expected

	while (!c.equals("y") && !c.equals("n")) {
	    System.out.println("Please answer y or n");
	    c = in.readLine();
	}

	while (c.equals("y")) {
	    sum(in);
	    System.out.println("Do you wish to calculate another sum? (y/n)");
	    c = in.readLine();

	    while (!c.equals("y") && !c.equals("n")) {
		System.out.println("Please answer y or n");
		c = in.readLine();
	    }
	}

	System.out.println("Goodbye");
    }
}

Please modify the program and add the suitable try-catch statement(s) so to cope with the following exceptions:

1. NumberFormatException: an exception of this kind means that the datum returned by in.readLine() does not represent an integer. If this occurs, the user should be asked to reenter the datum and continue.
2. IOException: an exception of this kind means that the readLine() operation could not be completed normally, for instance because of a coding error. Also in this case, the user should be asked to reenter the datum and continue.

Example of session:

java Sums

Do you wish to calculate a sum? (y/n)
y
Please input the sequence of integers to sum, terminated by a 0
20              
5
a
Invalid number. Please reenter.
2
0
The sum is 27
Do you wish to calculate another sum? (y/n)
s
Please input y or n
y
Please input the sequence of integers to sum, terminated by a 0
870
30
0
The sum is 900
Do you wish to calculate another sum? (y/n)
y    
Please input the sequence of integers to sum, terminated by a 0
0
The sum is 0
Do you wish to calculate another sum? (y/n)
n
Goodbye

Exercise 2 [Points 50]

public class PingPong extends Thread {
    private String word;  // what word to print
    private int delay;    // how long to pause (in milliseconds)
  
    public PingPong(String whatToSay, int delayTime) {
        word = whatToSay;
        delay = delayTime;
    }

    public void run() {
        try {
            for (;;) {
                System.out.print(word + " ");
                sleep(delay);   // pause before printing next word
            }
        } catch (InterruptedException e) {
            return;   // end this thread
        }
    }

    public static void main(String[] args) {
        new PingPong("ping",  33).start();  // 1/30 second
        new PingPong("PONG", 100).start();  // 1/10 second
    }
}

1. The number of threads
2. For each thread, the word to print and the number of milliseconds to sleep between two consecutive prints.

java PrintWords

please input the number of threads
3
please input the word of thread 1
din
please input the delay of thread 1
33
please input the word of thread 2
don
please input the delay of thread 2
33
please input the word of thread 3
dan
please input the delay of thread 3
33

din don dan din don dan din don dan din don 
dan din don dan din don dan din don dan din
don dan din don dan din don dan din don dan
...

Note: The order in which the threads are activated may be different from the above one. For instance, you could get don din dan don din dan ... instead. Also, the order may change (for instance, you could get don din dan dan don din ... ). This is normal, because the scheduling policy is unpredictable and in general differ from machine to machine.

Please note the following:.

1. Please make sure that your programs can be compiled with the Unix javac and executed with the Unix java. Programs which cannot be compiled or executed will receive, at most, 20 points.
2. Please call the classes of your programs Sums and PrintWords respectively, and save them in two files named Sums.java and PrintWords.java respectively. Make sure that the programs can be compiled and executed with the following commands:

          javac Sums.java
          java Sums
          

   and

          javac PrintWords.java
          java PrintWords
          

3. Its your responsibility to write sound, reliable programs, so please test your code thoroughly before submitting it.

Format of the solution