Explain exception propagation in Java | Java Interview Questions

Exception propagation is an important concept in Java that deals with how exceptions are passed through the method call stack.

When an exception occurs in a method, the method creates an object and hands it off to the runtime system. This object, called an exception object, contains information about the error, including its type and the state of the program when the error occurred. The process of creating the exception object and handing it over to the runtime system is called "throwing an exception".

After a method throws an exception, the runtime system attempts to find something to handle it. The set of possible "somethings" to handle the exception is determined by the method call stack—the list of methods that had been called to get to the method where the error occurred. The runtime system searches the call stack, from the method where the error occurred, to the first method of the call stack, looking for a method that contains a suitable exception handler.

This propagation continues until it finds a method that can handle it. If it doesn't find any such method, the program terminates.

Here is an example:

public class Main {

static void methodC() {
int i = 50 / 0; // This will throw an ArithmeticException
}

static void methodB() {
methodC();
}

static void methodA() {
try {
methodB();
} catch(ArithmeticException e) {
}
}

public static void main(String[] args) {
methodA();
}
}

In this example, an ArithmeticException is thrown in methodC. This exception is not handled in methodC, so it propagates to methodB. Again, it's not handled in methodB, so it propagates further to methodA. In methodA, there is a suitable exception handler, so the exception is caught and handled there. The program then continues with its normal flow.

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