Catching an Exception from a called Method

Question

This is something that\'s been bugging me for a while with regards to Program Flow.

I wanted to know if it\'s possible to catch an error from a Method in order to stop i

Answer 1

You put method01 and method02 in to same try block:

public class MyClass {

    public static void main(String[] args) {
        try {
            // This method catches an exception and stops running.
            method01();
            // This method will not continue if method01 have exception.
            method02();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

// declare method01, method02, others...

}

Notice: You have mistakes at the end of code block ( }; }; )

Answer 2

Depends on what your method really does.

If your program should continue working also when an exception arise (e.g. NumberFormatException when parsing an input or in general a checked exception) a lot of people will suggest you to not use exception for flow control, but IMHO in very well defined cases (like NumberFormatException) the flow CAN be controlled by try catch statements and exceptions, it's really up to you.

A way to do so is to use the method returned parameter (also @Nikola answer works in this way, the point is to use the catch part of a try catch as flow control):

public class MyClass {

   public static void main(String[] args) {

      if(method01()) method02();

   };
};

public boolean method01(){
    try{
        //some business
    }catch(MyCheckedException e){
        e.printStackTrace();
        return false;
    }
    return true;
}

NB: You should use this approach only in well defined situations! If a file CAN be absent in a directory while opening it (checked FileNotFoundException), you COULD use this approach. If the file SHOULD be there and its not, the exception MUST stop the program.

Answer 3

Can you try:

try {
    method01()
} catch (final Exception e) {
    // do something
    return; ///stop processing exit
}

the method01 will throw Exception:

private void method01() throws Exception {
// something
}

Answer 4

If you only want to terminate the whole program in case of an exception you just need to throw a RuntimeException without any further declaration. There are also specialized sub classes for explicit types of exceptions, like NullPointerException or IllegalStateException. See the "Direct Known Subclasses" section in the JavaDoc.

public class MyClass {

    public static void main(String[] args) {
        method01();
        method02(); //method02 won't be called in case of an exception
    }

    private static void method01() {
        // ...
        if (true) // something goes wrong
            throw new RuntimeException();
        // further code won't be executed in case of an exception
    }

    private static void method02() {
        System.out.println("method02 called");
    }
}

Optionally it is possible to handle the exception with a try-catch-block:

    public static void main(String[] args) {
        try {
            method01();
            method02(); // method02 won't be called in case of an exception
        } catch (Exception e) {
            System.err.println("something went wrong");
        }
    }

    // other code keeps unchanged...

If you want to enforce exception handling, you have to throw a subclass of Exception that is not derived from RuntimeException. But those exceptions have to be declared within the method Signature.

    private static void method01() throws IOException {
            throw new IOException();
    }