Try–catch block in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to catch an exception.

Java

try {
    int result = 10 / 0;
} catch ([1] e) {
    System.out.println("Error occurred");
}

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

Aint

BException

CString

Dvoid

Attempts:

3 left

💡 Hint

Common Mistakes

Using a data type like int or String instead of an exception type.

Leaving the catch parentheses empty.

The catch block must specify an exception type to catch errors. Exception is the general type for exceptions.

2fill in blank

medium

Complete the code to print the exception message.

Java

try {
    int[] arr = new int[2];
    System.out.println(arr[5]);
} catch (ArrayIndexOutOfBoundsException e) {
    System.out.println(e.[1]());
}

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

AtoString

BprintStackTrace

CgetMessage

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using printStackTrace() which prints the whole trace instead of just the message.

Using length which is not a method of exceptions.

The getMessage() method returns the error message of the exception.

3fill in blank

hard

Fix the error in the catch block declaration.

Java

try {
    int a = Integer.parseInt("abc");
} catch ([1] e) {
    System.out.println("Invalid number format");
}

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

ANumberFormatException

BNullPointerException

CIOException

DArithmeticException

Attempts:

3 left

💡 Hint

Common Mistakes

Using unrelated exceptions like IOException or ArithmeticException.

Not catching the specific exception thrown.

The parseInt method throws NumberFormatException when the string is not a valid number.

4fill in blank

hard

Fill both blanks to catch an exception and print its message.

Java

try {
    String s = null;
    System.out.println(s.length());
} catch ([1] e) {
    System.out.println(e.[2]());
}

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

ANullPointerException

BgetMessage

CprintStackTrace

DIOException

Attempts:

3 left

💡 Hint

Common Mistakes

Using IOException which is unrelated.

Using printStackTrace instead of getMessage.

The code throws a NullPointerException when calling length() on null. The getMessage() method prints the error message.

5fill in blank

hard

Fill all three blanks to catch an exception, print its message, and execute code after try-catch.

Java

try {
    int[] nums = {1, 2, 3};
    System.out.println(nums[[1]]);
} catch ([2] e) {
    System.out.println(e.[3]());
}
System.out.println("Program continues");

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

A5

BArrayIndexOutOfBoundsException

CgetMessage

DNullPointerException

Attempts:

3 left

💡 Hint

Common Mistakes

Using a valid index like 2 which does not cause an exception.

Using NullPointerException which is unrelated here.

Using printStackTrace instead of getMessage.

Accessing index 5 in an array of size 3 causes ArrayIndexOutOfBoundsException. The getMessage() method prints the error message. The program then continues after the catch block.

Practice

1. What is the main purpose of a try-catch block in Java?

easy

A. To create new classes

B. To handle errors and prevent program crashes

C. To declare variables

D. To repeat code multiple times

Solution

1. Step 1: Understand the role of try block

   The try block contains code that might cause an error during execution.

2. Step 2: Understand the role of catch block

   The catch block runs only if an error occurs, allowing the program to handle it gracefully.

3. Final Answer:

   To handle errors and prevent program crashes -> Option B

4. Quick Check:

   try-catch handles errors = D [OK]

Hint: Try-catch is for error handling, not loops or declarations [OK]

Common Mistakes:

• Confusing try-catch with loops
• Thinking try-catch declares variables
• Assuming try-catch creates classes

2. Which of the following is the correct syntax to catch an exception in Java?

easy

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

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

C. try { /* code */ } catch { /* handle */ }

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

Solution

1. Step 1: Check catch syntax

   The catch block must specify the exception type in parentheses, like catch (Exception e).

2. Step 2: Identify correct option

   try { /* code */ } catch (Exception e) { /* handle */ } correctly uses parentheses and exception type; others miss parentheses or type.

3. Final Answer:

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

4. Quick Check:

   Correct catch syntax = A [OK]

Hint: Catch must have parentheses with exception type [OK]

Common Mistakes:

• Omitting parentheses in catch
• Not specifying exception type
• Using wrong catch syntax

3. What will be the output of this code?

try {
  int a = 5 / 0;
  System.out.println("Result: " + a);
} catch (ArithmeticException e) {
  System.out.println("Error caught");
}

medium

A. Error caught

B. Result: 0

C. 5

D. Compilation error

Solution

1. Step 1: Identify the error in try block

   Dividing by zero causes an ArithmeticException at runtime.

2. Step 2: Check catch block response

   The catch block catches ArithmeticException and prints "Error caught".

3. Final Answer:

   Error caught -> Option A

4. Quick Check:

   Division by zero triggers catch = A [OK]

Hint: Division by zero triggers catch block output [OK]

Common Mistakes:

• Expecting normal output despite error
• Thinking code crashes without catch
• Confusing compile-time and runtime errors

4. Find the error in this code snippet:

try {
  int[] arr = new int[3];
  arr[5] = 10;
} catch (ArrayIndexOutOfBoundsException e) {
  System.out.println("Index error");
}

medium

A. Array size is too small

B. No error, code runs fine

C. Catch block syntax is wrong

D. Exception type is incorrect

Solution

1. Step 1: Analyze array usage

   Array declared with size 3, valid indices are 0,1,2; index 5 is out of bounds.

2. Step 2: Understand exception thrown

   Accessing index 5 causes ArrayIndexOutOfBoundsException, which is correctly caught.

3. Final Answer:

   Array size is too small -> Option A

4. Quick Check:

   Index 5 invalid for size 3 = C [OK]

Hint: Check array size vs accessed index to find error [OK]

Common Mistakes:

• Thinking catch syntax is wrong
• Assuming no error occurs
• Confusing exception types

5. You want to read an integer from user input safely. Which code correctly uses try-catch to handle invalid input?

import java.util.Scanner;

Scanner sc = new Scanner(System.in);
int num;
try {
  num = sc.nextInt();
  System.out.println("You entered: " + num);
} catch (Exception e) {
  System.out.println("Invalid input");
}

hard

A. Missing finally block causes error

B. Should catch IOException instead of Exception

C. Correctly handles invalid input with try-catch

D. Try block should be outside Scanner usage

Solution

1. Step 1: Understand input reading

   Using sc.nextInt() reads integer input; invalid input throws InputMismatchException, a subclass of Exception.

2. Step 2: Check try-catch usage

   The try block attempts input; catch block handles any Exception, printing "Invalid input" if input is wrong.

3. Final Answer:

   Correctly handles invalid input with try-catch -> Option C

4. Quick Check:

   Try-catch handles input errors = B [OK]

Hint: Catch Exception to handle all input errors safely [OK]

Common Mistakes:

• Thinking finally is mandatory
• Catching wrong exception type
• Placing try block incorrectly