Question

This programming assignment involves learning about some common exceptions which occur in Java programs. Consider the following exception types:

NullPointerException

ArrayIndexOutOfBounds

Exception ClassCastException

IllegalArgumentException

Research what each exception type means and the conditions under which each occurs (thrown). Then write the following programs, one for each of the above-listed exception types:

• A program which throws the exception (with a throw statement) and catches it displaying unique information about the exception. Name your programs <exception>Thrown.java

  <exception> is the name of the exception involved for example NullPointerExceptionThrown.java.

• A program which causes the exception to be thrown (not with a throw statement) and catches it displaying unique information about the exception (ex. Name of class and method causing the exception). For example, for the NullPointerException, have your program create a situation which would cause this exception to be thrown. Name your programs <exception>Catch.java <exception> is the name of the exception involved for example NullPointerExceptionCatch.java.

  At the end you should have eight programs, four <exception>Thrown.java and four <exception>Catch.java. All files should be in the same directory.

Answer 1

1st file

NullPointerExceptions are exceptions that occur when you try to use a reference that points to no location in memory (null) as though it were referencing an object.

NullPointerExceptionThrown.java

public class NullPointerExceptionThrown {
   public static void hasCode(){
       System.out.println("Do Something");
   }

public static void main(String[] args) {
Object a = null;
a.hashCode();
}

}

Output:

2nd File:

NullPointerExceptionCatch.java
public class NullPointerExceptionCatch {
   public static void hasCode(){
       System.out.println("Do Something");
   }

public static void main(String[] args) {
try {
   Object a = null;
       a.hashCode();
} catch(NullPointerException e) {
System.out.println("NullPointerException.. Handled");
}
}

}

3rd File

If a request for a negative or an index greater than or equal to size of array is made, then the JAVA throws a ArrayIndexOutOfBounds Exception.

ArrayIndexOutOfBoundThrown.java

public class ArrayIndexOutOfBoundThrown{
   public static void main(String[] args) {
       int[] arr=new int[5];
       int i=0;
       System.out.println(arr[6]);
   }
}

4th File

ArrayIndexOutOfBoundCatch.java

public class ArrayIndexOutOfBoundCatch{
   public static void main(String[] args) {
       try{
int[] arr=new int[5];
           int i=0;
           System.out.println(arr[6]);
}
catch(ArrayIndexOutOfBoundsException e){
System.out.println ("Array Index is Out Of Bounds");
}
   }
}

5th File

if you are trying to typecast an object of class A into an object of class B, and they aren't compatible, you get a class cast exception.

classCastExceptionThrown.java

public class classCastExceptionThrown {

public static void main(String[] args) {

   Object i = Integer.valueOf(42);
               String s = (String)i;

}

}

6th File

classCastExceptionCatch.java

public class classCastExceptionThrown {

public static void main(String[] args) {
        try{
            Object i = Integer.valueOf(42);
               String s = (String)i;
        } catch(ClassCastException e) {
System.out.println("ClassCastException.. Handled");
}

}

}

7th File

The IllegalArgumentException is a good way of handling possible errors in your application’s code. This exception indicates that a method is called with incorrect input arguments.

IllegalArgumentExceptionThrown.java

import java.io.File;

public class IllegalArgumentExceptionThrown {

public static String createRelativePath(String parent, String filename) {
if(parent == null)
throw new IllegalArgumentException("The parent path cannot be null!");

if(filename == null)
throw new IllegalArgumentException("The filename cannot be null!");

return parent + File.separator + filename;
}

public static void main(String[] args) {
// The following command will be successfully executed.
System.out.println(IllegalArgumentExceptionThrown.createRelativePath("dir1", "file1"));
System.out.println();

// The following command throws an IllegalArgumentException.
System.out.println(IllegalArgumentExceptionThrown.createRelativePath(null, "file1"));
}

}
}

8th File

IllegalArgumentExceptionCatch.java

import java.io.File;

public class IllegalArgumentExceptionCatch {

public static String createRelativePath(String parent, String filename) {
if(parent == null)
throw new IllegalArgumentException("The parent path cannot be null!");

if(filename == null)
throw new IllegalArgumentException("The filename cannot be null!");

return parent + File.separator + filename;
}

public static void main(String[] args) {
// The following command will be successfully executed.
try{
System.out.println(IllegalArgumentExceptionCatch.createRelativePath("dir1", "file1"));
System.out.println();

// The following command throws an IllegalArgumentException.
System.out.println(IllegalArgumentExceptionCatch.createRelativePath(null, "file1"));
} catch (IllegalArgumentException e){
System.out.println("IllegalArgumentException Handled !!");
}

}
}