Java Error Handling Basics-The story that catch is only picked up in the foreground

I'm really wondering where to pick up the error.

If you try-catch in a subroutine, you may not reach the place you want to pick up.

java was the same

Examples that do not reach

If the same Exception is thrown in a multi-stage subroutine, it can only be picked up in the inner subroutine.

public class MyException {
	final private static int[] M = {1,2,3}; 
	public static void main(String[] args) {
		try {
			subroutine(M);
		}
		catch ( ArrayIndexOutOfBoundsException e ) {
		   System.out.println("[SECOND] catch : " + e.getMessage());
		}
	}

	public static void subroutine(int[] M) throws ArrayIndexOutOfBoundsException {
		try {
			System.out.println(M[4]);
		}
		catch ( ArrayIndexOutOfBoundsException e ) {
		   System.out.println("[FIRST] catch : " + e.getMessage());
		}
	}
}

result

[FIRST] catch : Index 4 out of bounds for length 3

Example to arrive

If you throw it again in the inner catch, you can pick it up on the outside. When throwing, pass the argument e in a nice way. If it remains e, an error occurs. I'm not sure.

public class MyException {
	final private static int[] M = {1,2,3}; 
	public static void main(String[] args) {
		try {
			subroutine(M);
		}
		catch ( ArrayIndexOutOfBoundsException e ) {
		   System.out.println("[SECOND] catch : " + e.getMessage());
		}
	}

	public static void subroutine(int[] M) throws ArrayIndexOutOfBoundsException {
		try {
			System.out.println(M[4]);
		}
		catch ( ArrayIndexOutOfBoundsException e ) {
		   System.out.println("[FIRST] catch : " + e.getMessage());
		   throw new ArrayIndexOutOfBoundsException(e.getMessage());
        <---Throw
		}
	}
}

result

[FIRST] catch : Index 4 out of bounds for length 3
[SECOND] catch : Index 4 out of bounds for length 3

So what I mean is --It is easier to see where to pick up errors as much as possible ――But each module also has a role, so it is important to divide it within the scope of responsibility. --When delimiting, if you easily pick up Exception / RUntimeException, it will not reach the outside --You have to pick up a proper xxException as finely as possible inside. ――In order to do that, you need to know exactly what to do and what exception to come out. --If & throw is the best -(like if == 0: throw new DivededByZeroException)

reference http://math.hws.edu/javanotes/c8/s3.html

The last code here also consists of if + throw. I think I'm writing something like that, but I'm too sleepy to understand anymore, so I go to bed.

Well that kind of memo