Java Exception Handling Keywords

Exception handling is an essential part of writing robust Java programs. Java provides several keywords to handle exceptions efficiently.

Java provides several keywords and mechanisms to handle exceptions:

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try Block

The try block contains the code that might throw an exception.

If an exception occurs in the try block, it is caught by a corresponding catch block.
A try block must be followed by at least one catch block or a finally block.

Syntax:

try {
    // Code that may throw an exception
}
catch (ExceptionType e) {
    // Handling code
}

Example:

public class TryExample {
    public static void main(String[] args) {
        try {
            int result = 10 / 0; // May throw ArithmeticException
        } catch (ArithmeticException e) {
            System.out.println("Cannot divide by zero!");
        }
    }
}

Output:

Cannot divide by zero!

catch Block

The catch block handles the exception thrown in the try block.

You can have multiple catch blocks to handle different exception types.
Catch blocks are executed only when the corresponding exception occurs.

Example:

try {
    int[] arr = {1, 2, 3};
    System.out.println(arr[5]); // May throw ArrayIndexOutOfBoundsException
} catch (ArithmeticException e) {
    System.out.println("Arithmetic error");
} catch (ArrayIndexOutOfBoundsException e) {
    System.out.println("Array index out of bounds");
}

Output:

Array index out of bounds

finally Block

The finally block always executes, whether an exception occurs or not.

It is commonly used to release resources, like closing files or database connections.
Even if there is a return statement in try/catch, finally still executes.

Syntax:

try {
    // risky code
} catch (Exception e) {
    // exception handling
} finally {
    // always executes
}

Example:

try {
    int num = 10 / 2;
    System.out.println(num);
} catch (ArithmeticException e) {
    System.out.println("Cannot divide by zero");
} finally {
    System.out.println("This will always execute");
}

Output:

5
This will always execute

throw Keyword

The throw keyword is used to explicitly throw an exception in your code.

Can be used for checked or unchecked exceptions.
Often used in validation or custom error scenarios.

Syntax:

throw new ExceptionType("Error message");

Example:

public class ThrowExample {
    public static void main(String[] args) {
        int age = 15;
        if (age < 18) {
            throw new ArithmeticException("Age must be 18 or above");
        }
    }
}

Output:

Exception in thread "main" java.lang.ArithmeticException: Age must be 18 or above

throws Keyword

The throws keyword is used in method declarations to specify which exceptions might be thrown by that method.

The caller method is responsible for handling the exception.
Mostly used for checked exceptions.

Syntax:

returnType methodName() throws ExceptionType {
    // code that may throw exception
}

Example:

import java.io.*;

public class ThrowsExample {
    static void readFile() throws IOException {
        FileReader file = new FileReader("test.txt");
    }

    public static void main(String[] args) {
        try {
            readFile();
        } catch (IOException e) {
            System.out.println("File not found!");
        }
    }
}

Output (if file not present):

File not found!

Points to Remember

try block must be followed by either catch or finally.
Multiple catch blocks can handle different exception types.
finally always executes, even if there’s a return statement.
throw is used to throw an exception explicitly.
throws indicates potential exceptions in a method declaration.

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