Try‐Catch – Handling Errors Like a Safety Net

Sometimes, things go wrong in a program—just like in real life!

For example:

• You try to divide a number by zero (which is not allowed).
• You ask for a file that doesn’t exist.
• You try to use a Scanner, but the user enters the wrong type of input.

If we don’t handle these errors, our program crashes! 🚨

To prevent crashes, we use try-catch, which acts like a safety net to catch errors and handle them properly.

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1. What is Try-Catch?

🔹 try – The code that might cause an error goes inside this block.
🔹 catch – If an error happens, Java jumps here and handles the problem instead of crashing.

📌 Think of it like this:

• Try block: "Let’s try to do something."
• Catch block: "Oops! If something goes wrong, we’ll catch it and handle it."

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2. Example: Preventing a Crash When Dividing by Zero

public class TryCatchExample {
    public static void main(String[] args) {
        try {
            int number = 10 / 0; // This will cause an error!
            System.out.println("Result: " + number);
        } catch (ArithmeticException e) {
            System.out.println("Oops! You can't divide by zero.");
        }
        
        System.out.println("Program continues...");
    }
}

Output:

Oops! You can't divide by zero.
Program continues...

🚀 What Happened?

• Java tried to divide 10 by 0 (which is not allowed!).
• Instead of crashing, Java caught the error and printed "Oops! You can't divide by zero."
• The program continues running!

➡️ Without try-catch, the program would have crashed!

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3. Example: Handling Wrong User Input

Let’s say we ask the user for a number, but they enter a word instead. Normally, the program would crash—but with try-catch, we can handle it!

import java.util.Scanner;

public class TryCatchExample {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        try {
            System.out.print("Enter a number: ");
            int number = scanner.nextInt(); // What if the user enters a word?
            System.out.println("You entered: " + number);
        } catch (Exception e) {
            System.out.println("Oops! That's not a number.");
        }

        System.out.println("Program continues...");
    }
}

Example Run 1 (User enters a number)

Enter a number: 5  
You entered: 5  
Program continues...

Example Run 2 (User enters a word)

Enter a number: hello  
Oops! That's not a number.  
Program continues...

🚀 What Happened?

• If the user enters a number, everything works fine.
• If the user enters a word, Java catches the error and tells them instead of crashing!

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4. Multiple Catch Blocks – Handling Different Errors

Sometimes, different types of errors can happen. We can use multiple catch blocks to handle them separately.

public class MultiCatchExample {
    public static void main(String[] args) {
        try {
            int[] numbers = {1, 2, 3};
            System.out.println(numbers[5]); // This will cause an error!
        } catch (ArithmeticException e) {
            System.out.println("Math error!");
        } catch (ArrayIndexOutOfBoundsException e) {
            System.out.println("Oops! That index doesn't exist.");
        }
    }
}

Output:

Oops! That index doesn't exist.

➡️ Java tried to access numbers[5], but the array only has 3 numbers!
➡️ It caught the correct error (ArrayIndexOutOfBoundsException) and handled it.

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5. Finally – Always Runs No Matter What

Sometimes, we always need to run some code—whether there was an error or not.

📌 Example: Closing a File or Scanner After Using It

import java.util.Scanner;

public class TryCatchFinallyExample {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        try {
            System.out.print("Enter a number: ");
            int number = scanner.nextInt();
            System.out.println("You entered: " + number);
        } catch (Exception e) {
            System.out.println("Oops! That's not a number.");
        } finally {
            scanner.close(); // Always runs to close the scanner
            System.out.println("Scanner closed. Program ending.");
        }
    }
}

Example Run 1 (User enters a number)

Enter a number: 10  
You entered: 10  
Scanner closed. Program ending.

Example Run 2 (User enters a word)

Enter a number: abc  
Oops! That's not a number.  
Scanner closed. Program ending.

➡️ The finally block always runs!
➡️ We used it to close the scanner (good practice).

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Final Takeaway: When to Use Try-Catch?

Situation	What Can Go Wrong?	How Try-Catch Helps
Dividing Numbers	Division by zero crashes the program	Catch the error and show a message
Getting User Input	User enters wrong data type	Prevent crash and ask again
Reading Files	File might not exist	Handle error and show message
Using Arrays	Trying to access an index that doesn’t exist	Avoid crashes and notify user

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That’s try-catch! 🎉