Why exception handling is required in Java - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to catch an exception when dividing by zero.

Java

try {
    int result = 10 / [1];
} catch (ArithmeticException e) {
    System.out.println("Cannot divide by zero.");
}

Drag options to blanks, or click blank then click option'

A10

B1

C2

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-zero number which does not cause an exception.

Dividing by zero causes an ArithmeticException, so the blank must be 0 to trigger the exception.

2fill in blank

medium

Complete the code to handle a possible null pointer exception.

Java

String text = null;
try {
    int length = text.[1]();
} catch (NullPointerException e) {
    System.out.println("Text is null.");
}

Drag options to blanks, or click blank then click option'

Alength()

BcharAt

Clength

DtoString

Attempts:

3 left

💡 Hint

Common Mistakes

Using length without parentheses which is invalid for String.

The method length() is called on a null string, which causes NullPointerException.

3fill in blank

hard

Fix the error in the code to properly catch exceptions.

Java

try {
    int[] arr = new int[3];
    int value = arr[5];
} catch ([1] e) {
    System.out.println("Index out of bounds.");
}

Drag options to blanks, or click blank then click option'

AArithmeticException

BNullPointerException

CArrayIndexOutOfBoundsException

DIOException

Attempts:

3 left

💡 Hint

Common Mistakes

Catching the wrong exception type that does not match the error.

Accessing an invalid array index throws ArrayIndexOutOfBoundsException.

4fill in blank

hard

Fill both blanks to create a try-catch block that handles file reading exceptions.

Java

try {
    FileReader file = new FileReader("test.txt");
    BufferedReader reader = new BufferedReader(file);
    String line = reader.readLine();
} catch ([1] e) {
    System.out.println("File not found.");
} catch ([2] e) {
    System.out.println("IO error occurred.");
}

Drag options to blanks, or click blank then click option'

AFileNotFoundException

BNullPointerException

CIOException

DArithmeticException

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the order of exceptions or using unrelated exceptions.

FileNotFoundException handles missing file errors, IOException handles other input/output errors.

5fill in blank

hard

Fill all three blanks to create a method that throws and catches a custom exception.

Java

class MyException extends Exception {}

public class Test {
    public static void check(int num) throws [1] {
        if (num < 0) {
            throw new [2]();
        }
    }

    public static void main(String[] args) {
        try {
            check(-1);
        } catch ([3] e) {
            System.out.println("Custom exception caught.");
        }
    }
}

Drag options to blanks, or click blank then click option'

AMyException

DException

Attempts:

3 left

💡 Hint

Common Mistakes

Using Exception instead of the custom exception class.

The method declares throwing MyException, throws it when condition meets, and catches it in main.

Practice

1. Why is exception handling required in Java programs?

easy

A. To prevent the program from crashing when an error occurs

B. To make the program run faster

C. To increase the size of the program

D. To avoid writing any code

Solution

1. Step 1: Understand what happens without exception handling

   Without exception handling, errors cause the program to stop abruptly, leading to crashes.

2. Step 2: Role of exception handling

   Exception handling catches errors and allows the program to continue or handle the error gracefully.

3. Final Answer:

   To prevent the program from crashing when an error occurs -> Option A

4. Quick Check:

   Exception handling prevents crashes [OK]

Hint: Exception handling stops crashes by managing errors [OK]

Common Mistakes:

• Thinking exception handling makes code faster
• Believing it increases program size unnecessarily
• Assuming it removes the need to write code

2. Which of the following is the correct syntax to start exception handling in Java?

easy

A. try(Exception e) { /* code */ } catch { /* handle */ }

B. catch { /* code */ } try(Exception e) { /* handle */ }

C. handle { /* code */ } try(Exception e) { /* handle */ }

D. try { /* code */ } catch(Exception e) { /* handle */ }

Solution

1. Step 1: Identify the correct order of try-catch blocks

   In Java, the try block comes first, followed by one or more catch blocks.

2. Step 2: Check syntax correctness

   try { /* code */ } catch(Exception e) { /* handle */ } correctly uses try { } followed by catch(Exception e) { } which is valid syntax.

3. Final Answer:

   try { /* code */ } catch(Exception e) { /* handle */ } -> Option D

4. Quick Check:

   try block first, then catch [OK]

Hint: Try block comes before catch block in Java syntax [OK]

Common Mistakes:

• Swapping try and catch keywords
• Using 'handle' instead of 'catch'
• Placing exception parameter incorrectly

3. What will be the output of the following Java code?

public class Test {
  public static void main(String[] args) {
    try {
      int result = 10 / 0;
      System.out.println(result);
    } catch (ArithmeticException e) {
      System.out.println("Error caught: " + e.getMessage());
    }
  }
}

medium

A. Error caught: / by zero

B. 10

C. 0

D. Program crashes with ArithmeticException

Solution

1. Step 1: Identify the error in the try block

   The code attempts to divide 10 by 0, which causes an ArithmeticException.

2. Step 2: Check how the exception is handled

   The catch block catches ArithmeticException and prints "Error caught: " plus the exception message "/ by zero".

3. Final Answer:

   Error caught: / by zero -> Option A

4. Quick Check:

   Division by zero caught and message printed [OK]

Hint: Division by zero triggers ArithmeticException caught by catch [OK]

Common Mistakes:

• Expecting program to print 10 or 0
• Thinking program crashes without catch
• Ignoring exception message in output

4. Identify the error in the following Java code snippet related to exception handling:

try {
  int[] arr = new int[3];
  System.out.println(arr[5]);
} catch (Exception e) {
  System.out.println("Exception caught");
}

medium

A. ArrayIndexOutOfBoundsException is not caught because catch is for Exception

B. The code will compile but throw an uncaught exception

C. No error; the exception will be caught and message printed

D. Syntax error in try-catch block

Solution

1. Step 1: Understand the exception thrown

   Accessing arr[5] causes ArrayIndexOutOfBoundsException, which is a subclass of Exception.

2. Step 2: Check catch block type

   The catch block catches Exception, so it will catch ArrayIndexOutOfBoundsException and print the message.

3. Final Answer:

   No error; the exception will be caught and message printed -> Option C

4. Quick Check:

   Exception catch block catches all exceptions [OK]

Hint: Catch Exception catches all exceptions including subclasses [OK]

Common Mistakes:

• Thinking ArrayIndexOutOfBoundsException is not caught by Exception
• Assuming code crashes without catch
• Believing syntax error exists in try-catch

5. You want to read a file in Java but ensure the program continues even if the file is missing. Which approach best uses exception handling to achieve this?

hard

A. Use if-else to check file existence without try-catch

B. Use try block to read file and catch FileNotFoundException to handle missing file

C. Use only catch block without try block

D. Ignore exceptions and let the program crash if file is missing

Solution

1. Step 1: Understand the problem of missing file

   Reading a missing file throws FileNotFoundException, which must be handled to avoid crash.

2. Step 2: Use try-catch to handle exception

   Placing file reading code inside try and catching FileNotFoundException allows graceful handling and program continuation.

3. Final Answer:

   Use try block to read file and catch FileNotFoundException to handle missing file -> Option B

4. Quick Check:

   Try-catch handles file errors to keep program running [OK]

Hint: Try reading file, catch FileNotFoundException to avoid crash [OK]

Common Mistakes:

• Ignoring exceptions causing program crash
• Using catch without try block
• Relying only on if-else without exception handling