In Java, the throw keyword is used to throw an exception explicitly. When an exception is thrown using the throw keyword, the control is transferred to the catch block where the exception can be caught and handled appropriately.
Here’s an example of how to use throw in Java:
public void someMethod() throws Exception {
// some code here
if (someCondition) {
throw new Exception("Some error occurred.");
}
// some more code here
}
In this example, the someMethod() method may throw an exception of type Exception if the someCondition is true. If the exception is thrown, the message “Some error occurred.” will be passed as the argument to the constructor of the Exception class.
The throws keyword in the method signature indicates that this method may throw an exception of type Exception. Any code that calls this method must handle this exception or declare that it may also throw this exception.
Keep in mind that it’s important to handle exceptions appropriately in your code to ensure that your program can recover from errors and continue to execute without crashing.
Java throw keyword:
In Java, the throw keyword is used to throw an exception explicitly. The syntax for using throw keyword is:
throw throwableInstance;
Where throwableInstance is an object of a class that extends the Throwable class, such as Exception or RuntimeException.
When the throw keyword is used, it causes an exception to be thrown at the point where it appears in the code. The control is then transferred to the catch block, where the exception can be caught and handled appropriately.
Here’s an example of using the throw keyword to throw a custom exception:
public void someMethod() throws CustomException {
// some code here
if (someCondition) {
throw new CustomException("Some error occurred.");
}
// some more code here
}
In this example, the someMethod() method may throw a custom exception of type CustomException if the someCondition is true. If the exception is thrown, the message “Some error occurred.” will be passed as the argument to the constructor of the CustomException class.
It’s important to handle exceptions appropriately in your code to ensure that your program can recover from errors and continue to execute without crashing.
Example 1: Throwing Unchecked Exception:
Here’s an example of throwing an unchecked exception in Java using the throw keyword:
public class Example {
public static void main(String[] args) {
int num = 10;
if (num < 100) {
throw new RuntimeException("Number is too small");
}
}
}
In this example, we have a simple Java program that checks if the value of the num variable is less than 100. If it is, we throw a RuntimeException with the message “Number is too small” using the throw keyword. Since RuntimeException is an unchecked exception, we don’t have to declare it in the throws clause of the method.
If the num variable is indeed less than 100, the program will throw the RuntimeException and terminate with an error message. If the value of num is greater than or equal to 100, the program will continue to execute without throwing an exception.
Keep in mind that it’s generally not a good practice to throw unchecked exceptions unless there is a good reason to do so. Unchecked exceptions should be used for unexpected and unrecoverable errors, while checked exceptions should be used for recoverable errors that can be handled by the caller of the method.
Example 2: Throwing Checked Exception:
Here’s an example of throwing a checked exception in Java using the throw keyword:
import java.io.IOException;
public class Example {
public static void main(String[] args) throws IOException {
throw new IOException("File not found");
}
}
In this example, we have a Java program that throws a IOException with the message “File not found” using the throw keyword. Since IOException is a checked exception, we have to declare it in the throws clause of the method, or handle it with a try-catch block.
If we don’t handle the exception with a try-catch block or declare it in the throws clause of the method, the compiler will generate a compile-time error. This ensures that any code that calls this method will be forced to handle the IOException in some way.
Keep in mind that it’s important to handle checked exceptions appropriately in your code to ensure that your program can recover from errors and continue to execute without crashing. In general, it’s a good practice to handle checked exceptions with a try-catch block, or declare them in the throws clause of the method if you want the caller of the method to handle the exception.
Example 3: Throwing User-defined Exception:
Here’s an example of throwing a user-defined exception in Java using the throw keyword:
public class Example {
public static void main(String[] args) {
try {
int num = 10;
if (num < 100) {
throw new CustomException("Number is too small");
}
} catch (CustomException e) {
System.out.println(e.getMessage());
}
}
}
class CustomException extends Exception {
public CustomException(String message) {
super(message);
}
}
In this example, we define a custom exception called CustomException by extending the Exception class. We then use the throw keyword to throw a CustomException with the message “Number is too small” inside a try block.
Since CustomException is a checked exception, we have to catch it with a catch block or declare it in the throws clause of the method. In this example, we catch the CustomException and print the error message to the console.
If the value of num is less than 100, the program will throw the CustomException and execute the catch block. If the value of num is greater than or equal to 100, the program will continue to execute without throwing an exception.
Keep in mind that it’s a good practice to define custom exceptions for specific errors in your program. This makes it easier to handle these errors in a consistent and predictable way throughout your code.