Catch NumberFormatException has different behaviour?-CodePudding

I was writing a code to show examples of try/catch and I notice that the same catch NumberFormatException was triggered or not depending on where I use it. This is the code:

public class Main {
public static void main(String[] args) {

    System.out.println("3/0 => Result: "   divide(3,0));  // returns 3/0 => Result: null
    System.out.println("6/2 => Result: "   divide(6,2));  // returns 3/0 => Result: 3
//        System.out.println("6/home => Result: "   divide(Integer.parseInt("home"),1));

    try {
        System.out.println("6/home => Result: "   divide(Integer.parseInt("home"),1));
    } catch (NumberFormatException e) {
        System.out.println("Error type: NumberFormatException (MAIN METHOD)");
    }
}

static Integer divide(int n1, int n2) {   // we used Integer (wrapper class) to be able to return null

    int result = 0;

    try {
        result = n1 / n2;
    } catch (ArithmeticException e) {
        System.out.println("Error type: ArithmeticException");
        return null;
    } catch (NumberFormatException e) {
        System.out.println("Error type: NumberFormatException");
        return null;
    }
    return result;
}
}

The code returns:

Error type: ArithmeticException
3/0 => Result: null
6/2 => Result: 3
Error type: NumberFormatException (MAIN METHOD)

But if I enable the 3rd line:

System.out.println("6/home => Result: "   divide(Integer.parseInt("home"),1));

And disable the try/catch inside main method the NumberFormatException inside the divide method does not trigger and it crash the program.

Can anyone explain why? I am using the same exception type, why it works inside the main method but it does not work inside the divide method?

CodePudding user response：

Catching exceptions is depending on the exception happening inside the corresponsing try{} block. By disabling the try / catch inside the main method the occuring number format exception is not in any try{} block anymore and therefore "crashes" your program. The try / catch inside the divide method is in that case never even reached, as the exception happens while the thread is executing the code 'Integer.parseInt("home")' which is outisde of that block / inside your main method.

CodePudding user response：

It's because the Integer.parseInt method is called from the main method and not inside try / catch block. Look at the stack trace that should be printed out.

Exception in thread "main" java.lang.NumberFormatException: For input string: "home"
    at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
    at java.lang.Integer.parseInt(Integer.java:580)
    at java.lang.Integer.parseInt(Integer.java:615)
    at Main.main(Main.java:6)

The last line (Main.main(Main.java:6)) is giving you a clear hint from where the exception was thrown out in your code.