Question

IN JAVA:

1. Write a class, ZeroException, which is an Exception, and is used to signal that something is zero when it shouldn't be.
2. Write the class ArrayManipulator which creates an array and provides several methods to manipulate values taken from an array.

ZeroException Task:

Exceptions are used to signal many types of problems in a program. We can write our own as well to describe specific exceptional conditions which may arise. The advantage of doing so is that when exceptions are thrown, we can use the type of the exception we've created to identify the problem from among a set of other possible problems.

Here we have invented the notion of a "zero exception," which we would use to indicate that something has a zero value when it shouldn't. So in our main task below, we have a class which can return values but is not allowed to return a zero (for whatever arbitrary reason). Thus, whenever it is supposed to return a value, and the value happens to be zero, it will throw a ZeroExceptioninstead. Do not confuse this with a divide by zero error. This class will be fairly simple: the only constructor we will expect to be able to call is a default constructor (truly, we hardly need to put anything in the class for it to work - an exception's job is only to report that an error happened, so it really only needs to exist to do its work).

ArrayManipulator Task:

(7pts) Now we write a simple class which stores an array and allows us to set or get elements of the array. The getters include methods which manipulate values before returning them (i.e. multiply the number by a constant or divide the number by a constant). We will add one more constraint: the getters must never return a zero value. Instead, whenever we have a zero value, we would throw a zero exception instead.

The class should implement the following public methods:

• public ArrayManipulator(int size) Initialize an internal array of integers using the given size.
• public void set(int i, int v) A setter which sets the value at index i of the array to v.
• public int get(int i) A getter which gets the value at index i of the array. However, if the value would be zero, it should throw a ZeroException instead.
• public int getMult(int i, int m) A getter which gets the value at index i of the array and returns the product of that value and m. It should not change the value in the array, just return the result. However, if the result would be zero, it should throw a ZeroException instead.
• public int getDiv(int i, int d) A getter which gets the value at index i of the array and returns that value divided by d. It should not change the value in the array, just return the result. However, if the result would be zero, it should throw a ZeroException instead.
• public void print(int mode, int i, int v) This method will call either get(), getMult(), or getDiv(), depending on the mode parameter which is passed in, and print the result. If mode==0 then it calls get(), if mode==1 then it calls getMult(), and if mode==2 then it calls getDiv(). For any other value of mode, it will do nothing. It will make the call using i as the index and (if necessary) v as the value. If the result of the call is a division by zero, then print "divide by zero" instead. If the result is an out-of-bounds array access, then "out of bounds" should be printed. Finally, if the result of the operation is an illegal zero, then "zero results" should be printed.

Test Cases:

import org.junit.*;
import static org.junit.Assert.*;
import java.util.*;
import java.io.*;

public class E9tester {
  public static void main(String args[]){
    org.junit.runner.JUnitCore.main("E9tester");
  }
  
  @Test public void zeroexception_exists() {
    Exception e = new ZeroException();
  }

  @Test public void arraymanipulator_getset() throws Exception {
    ArrayManipulator a = new ArrayManipulator(5);
    for (int i = 0;  i < 5;  i++) a.set(i, i+1);
    for (int i = 0;  i < 5;  i++) {
      String errMsg = String.format("incorrect value at position %d", i);
      assertEquals(errMsg, (i+1), a.get(i));
    }
    
  }
  
  private int[][] multRes = { 
    {1,2,3,4,5}, {2,4,6,8,10}, {3,6,9,12,15}, {4,8,12,16,20}, {5,10,15,20,25} 
  };
  @Test public void arraymanipulator_getmult() throws Exception {
    ArrayManipulator a = new ArrayManipulator(5);
    for (int i = 0;  i < 5;  i++) a.set(i, i+1);
    for (int[] testCase : multRes) {
       int m = testCase[0];
       for (int i = 0;  i < 5;  i++) {
         String errMsg = String.format("incorrect value at position %d when multiplying %d by %d", i, i+1, m);
         assertEquals(errMsg, testCase[i], a.getMult(i, m));
       }
       for (int i = 0;  i < 5;  i++) {
         String errMsg = String.format("incorrect value at position %d when multiplying %d by %d (repeated)", i, i+1, m);
         assertEquals(errMsg, testCase[i], a.getMult(i, m));
       }
    }
  }
  
  private int[][] divRes = { 
    {5,10,15,20,25,1}, {2,5,7,10,12,2}, {1,3,5,6,8,3}, {1,2,3,5,6,4}, {1,2,3,4,5,5} 
  };
  @Test public void arraymanipulator_getdiv() throws Exception {
    ArrayManipulator a = new ArrayManipulator(5);
    for (int i = 0;  i < 5;  i++) a.set(i, 5*i+5);
    for (int[] testCase : divRes) {
       int d = testCase[5];
       for (int i = 0;  i < 5;  i++) {
         String errMsg = String.format("incorrect value at position %d when dividing %d by %d", i, (5*i+5), d);
         assertEquals(errMsg, testCase[i], a.getDiv(i, d));
       }
       for (int i = 0;  i < 5;  i++) {
         String errMsg = String.format("incorrect value at position %d when dividing %d by %d (repeated)", i, (5*i+5), d);
         assertEquals(errMsg, testCase[i], a.getDiv(i, d));
       }
    }
  }
  
  @Test public void arraymanipulator_print() throws Exception {
    ArrayManipulator a = new ArrayManipulator(5);
    for (int i = 0;  i < 5;  i++) a.set(i, i+1);
    setCapture();
    for (int m = 0; m < 5; m++) {
      for (int i = 0;  i < 5;  i++) a.print(m,i,2);
    }
    a.print(0,10,0);
    a.print(1,10,0);
    a.print(2,10,0);
    a.print(0,0,0);
    a.print(1,0,0);
    a.print(2,0,0);
    a.set(0,0);
    a.print(0,0,0);
    
    String expected = "1\n2\n3\n4\n5\n"+
         "2\n4\n6\n8\n10\n"+
         "zero result\n1\n1\n2\n2\n"+
         "out of bounds\nout of bounds\nout of bounds\n" +
         "1\nzero result\ndivide by zero\n" +
         "zero result\n";
         
    String actual = getCapture();
        assertEquals(expected, actual);
    unsetCapture();
    
  }
  
  /** the lines below are for setting up input/output redirection so that the
    * tests can see what is being set to the screen as well as produce its own
    * pseudo-keyboard input.  No test appear below here. */
  
  static ByteArrayOutputStream localOut, localErr;
  static PrintStream sOut, sErr;

  @BeforeClass public static void setup() throws Exception {
    sOut = System.out;
    sErr = System.err;
  }
  
  @AfterClass public static void cleanup() throws Exception {
    unsetCapture();
  }
  
  private static void setCapture() {
   localOut = new ByteArrayOutputStream();
   localErr = new ByteArrayOutputStream();
   System.setOut(new PrintStream( localOut ) );
   System.setErr(new PrintStream( localErr ) );
  }

  private static String getCapture() {
   return localOut.toString().replaceAll("\\r?\\n", "\n");
  }

  private static void unsetCapture() {
   System.setOut( null );
   System.setOut( sOut );
   System.setErr( null );
   System.setErr( sErr );
  }

}

Answer 1

ZeroException.java:

public class ZeroException extends Exception{
    public ZeroException(){
        super();
    }

    public ZeroException(String message){
        super(message);
    }
}

---------------------------------------------------------------------------------------

ArrayManipulator.java:

public class ArrayManipulator{

    private int array[];

    public ArrayManipulator(int size){
        array = new int[size];
    }

    public int get(int i) throws ZeroException{
        if(array[i] == 0){
            throw new ZeroException("zero exception");
        }
        return array[i];
    }

    public void set(int i, int v) throws ZeroException{
        if(v == 0){
            throw new ZeroException("zero exception");
        }
        array[i] = v;
    }

    public int getMult(int i, int m) throws ZeroException{
        int result = array[i] * m;
        if(result == 0){
            throw new ZeroException("zero exception");
        }
        return result;
    }

    public int getDiv(int i, int d) throws ZeroException{
        int result = array[i] / d;
        if(result == 0){
            throw new ZeroException("zero exception");
        }
        return result;
    }

    public void print(int mode, int i, int v){
        try {
            switch (mode) {
                case 0:
                    get(i);
                    break;
                case 1:
                    getMult(i, v);
                    break;
                case 2:
                    getDiv(i, v);
                    break;
            }
        }
        catch(ArithmeticException ex){
            System.out.println("Divide by zero");
        }
        catch(ArrayIndexOutOfBoundsException ex){
            System.out.println("out of bounds");
        }
        catch(ZeroException ex){
            ex.getMessage();
        }
    }
}