In Java, an exception is an event that occurs during the execution of a program and disrupts the normal flow of instructions. When an exception is thrown, it can be caught and handled by the program, or it can propagate up the call stack until it reaches the top level of the program, at which point it will terminate the program.
There are two types of exceptions in Java: checked and unchecked. Checked exceptions are those that are checked at compile-time, and the programmer must explicitly handle them or declare that they are thrown in the method signature. Examples of checked exceptions include IOException and SQLException. Unchecked exceptions are those that are not checked at compile-time, and the programmer does not need to explicitly handle them. Examples of unchecked exceptions include NullPointerException and ArrayIndexOutOfBoundsException.
To handle exceptions in Java, you use a try-catch block. The try block contains the code that may throw an exception, and the catch block contains the code that handles the exception. Here’s an example:
try {
// code that may throw an exception
} catch (Exception e) {
// code that handles the exception
}
In this example, we use a try-catch block to handle an exception. If an exception is thrown in the try block, it will be caught by the catch block, which will handle it.
You can also use a finally block to execute code that should always be executed, regardless of whether an exception is thrown or not. Here’s an example:
try {
// code that may throw an exception
} catch (Exception e) {
// code that handles the exception
} finally {
// code that should always be executed
}
In this example, the finally block contains code that should always be executed, even if an exception is thrown and caught in the catch block.
You can also create your own custom exceptions by creating a class that extends the Exception class. Here’s an example:
public class MyException extends Exception {
public MyException(String message) {
super(message);
}
}
// ...
try {
// code that may throw MyException
} catch (MyException e) {
// code that handles MyException
}
In this example, we create a custom exception called MyException that extends the Exception class. We can then use a try-catch block to catch instances of MyException and handle them.
To summarize, exceptions are a powerful mechanism in Java for handling unexpected events that can occur during the execution of a program. By using try-catch blocks and custom exception classes, you can handle exceptions in a way that allows your program to continue executing in a well-defined and predictable manner.