Question

Introduction

In this lab we will look at the information given by thrown exceptions. In particular, we will see that a given design does not give the most useful information that it could. We will explore how to fix it.

The Program

We have three classes in the project. StringArray is similar to the class in the homework, with much functionality removed. Names is meant to be a collection of names that has a StringArray used to store them. It has a method used to check if a given name is stored at a certain index. Finally, Driver tries adding some names to a Names object and then tests if a certain name exists at various indices.

The Problem

When you run your driver, you don’t get the most useful information. The console just informs you that something broke. This is not very specific or informative. Your task is to investigate why the information given is so poor, and fix the problem.

To Get Credit

Bare minimum: Write a correct written explanation of the problem with the design. How is this program failing to use exceptions in the most useful way? Describe how it could be fixed.

Good: Fix the problem in the code. When the Driver runs, different errors should give different, useful output.

Excellent: Change the program so that it crashes after printing out the error message. When it crashes, make sure the stack trace takes you all the way to the original source of the crash.

public class Driver {

    

     static String[] array = new String[] {"Inez","Jayne","Malikah","Tymoteusz","Lilli","Israr",null,"Christos", "Misaki"};

    

     public static void main(String args[]){

          Names names = new Names(array);

          for(int i=0; i<10; i++) {

               try {

                     boolean result = names.containsAt("Malikah", i);

                     System.out.println("Index " + i + " contains \'should\'? " + result);

               }

               catch (RuntimeException ex) {

                     System.out.println("Index " + i + " contains \'should\'? " + ex.getMessage());

               }

          }

     }

    

}

public class Names {

     private StringArray nameArr;

    

     public Names(String[] names) {

          nameArr = new StringArray(names);

     }

    

     /**

     * Check if the string stored at index is the same as the given string

     * @param string to compare to

     * @param index to look at

     * @throws RuntimeException if something breaks

     * @return whether the string at the index is the same as the given string

     */

     public boolean containsAt(String string, int index) {

          try {

               return(nameArr.retrieveStringAt(index).contentEquals(string));

          }

          catch(IllegalArgumentException | NullPointerException ex) {

               throw new RuntimeException("something broke");

          }

     }

}

/*

* A class that stores a number of Strings in an array.

* It provides a number of methods to interact with the Strings.

* Null references are allowed in the String array

*/

public class StringArray {

    

     private String arr[];

    

     /**

     * Constructor for the SuperStringArray class

     * @param arr the string array to store in this object

     */

     public StringArray(String[] arr) {

          this.arr = arr;

     }

    

    

     @Override

     public String toString(){

          return arr.length + " String(s)";

     }

    

    

     public String retrieveStringAt(int stringIndex){

          if (stringIndex < 0 || stringIndex >= arr.length)

               throw new IllegalArgumentException("the index " + stringIndex + " is out of bounds");

          return arr[stringIndex];

     }

    

    

}

Answer 1

Please rate the answer and do comment in case of any query. Thanks.

Program flow:

1. containsAt() method is called in main method of ‘Driver’ class
2. retrieveStringAt() method is called in containsAt() method of ‘Names’ class

retrieveStringAt() method throws IllegalArgumentException if index is out of bounds. This exception is caught in containsAt() method of ‘Names’ class, but instead of throwing the exception which it received, a new RunTimeException is being created with a custom message – “something broke”. So the actual reason for exception is not being displayed.

Similarly, when a NullPointerException is thrown, containsAt() method of 'Names' class throws the same custom error message - "something broke" instead of the actual error message.

Fix/Solution:

Instead of returning the custom message by throwing the RunTimeException, throwing the actual error message (ex) can fix and display the same instead of “something broke”.

["throw new RuntimeException("something broke");" has been modified to "throw ex;"]

Note: There is no change in StringArray.java file

The modified classes are shown below:

Names.java:

public class Names {
private StringArray nameArr;

public Names(String[] names) {
nameArr = new StringArray(names);
}

/**
* Check if the string stored at index is the same as the given string
* @param string to compare to
* @param index to look at
* @throws RuntimeException if something breaks
* @return whether the string at the index is the same as the given string
*/
public boolean containsAt(String string, int index) {
try {
return(nameArr.retrieveStringAt(index).contentEquals(string));
}
catch(IllegalArgumentException | NullPointerException ex) {
throw ex;
}
}
}

Driver.java:

public class Driver {
static String[] array = new String[] {"Inez","Jayne","Malikah","Tymoteusz","Lilli","Israr",null,"Christos", "Misaki"};

public static void main(String args[]){
Names names = new Names(array);
for(int i=0; i<10; i++) {
try {
boolean result = names.containsAt("Malikah", i);
System.out.println("Index " + i + " contains \'Malikah\'? " + result);
}
catch (Exception ex) {
System.out.print("Index " + i + " contains \'Malikah\'? ");
ex.printStackTrace();
}
}
}
}

Screenshot of the modified code is shown below:

Names.java:

Screenshot of sample output is shown below:

************************************** Crashing the program after printing error message **************************************

Removing the exception handling (try-catch) mechanism in Driver.java crashes the program after printing the error message.

Note: There is no change in StringArray.java file

Code:

Names.java:

public class Names {
private StringArray nameArr;

public Names(String[] names) {
nameArr = new StringArray(names);
}

/**
* Check if the string stored at index is the same as the given string
* @param string to compare to
* @param index to look at
* @throws RuntimeException if something breaks
* @return whether the string at the index is the same as the given string
*/
public boolean containsAt(String string, int index) {
try {
return(nameArr.retrieveStringAt(index).contentEquals(string));
}
catch(IllegalArgumentException | NullPointerException ex) {
throw ex;
}
}
}

Driver.java:

public class Driver {
static String[] array = new String[] {"Inez","Jayne","Malikah","Tymoteusz","Lilli","Israr",null,"Christos", "Misaki"};

public static void main(String args[]){
Names names = new Names(array);
for(int i=0; i<10; i++) {
boolean result = names.containsAt("Malikah", i);
System.out.println("Index " + i + " contains \'Malikah\'? " + result);
}
}
}

Screenshots:

Names.java:

Driver.java:

Sample output:

Hope this helps you and would suffice your requirement.