Try–catch block in Java

Introduction

A try-catch block helps your program handle errors without crashing. It lets you try some code and catch problems if they happen.

When reading a file that might not exist.

When dividing numbers and the divisor could be zero.

When converting text to numbers that might be wrong.

When working with network connections that can fail.

Syntax

Java

try {
    // code that might cause an error
} catch (ExceptionType name) {
    // code to handle the error
}

The try block contains code that might cause an error.

The catch block runs only if an error happens in the try block.

Examples

This catches a division by zero error and prints a message.

Java

try {
    int result = 10 / 0;
} catch (ArithmeticException e) {
    System.out.println("Cannot divide by zero.");
}

This catches an error when trying to use a null text.

Java

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

Sample Program

This program tries to access an array element that does not exist. The catch block handles the error and the program keeps running.

Java

public class TryCatchExample {
    public static void main(String[] args) {
        try {
            int[] numbers = {1, 2, 3};
            System.out.println(numbers[5]);
        } catch (ArrayIndexOutOfBoundsException e) {
            System.out.println("Oops! Index is out of range.");
        }
        System.out.println("Program continues smoothly.");
    }
}

Important Notes

You can have multiple catch blocks to handle different errors.

Try-catch blocks help keep your program from stopping unexpectedly.

Summary

Use try-catch to handle errors safely.

The try block runs code that might fail.

The catch block runs if an error happens, letting you respond nicely.

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