throws - Question

[Zhenya]

Good afternoon for everyone!
I have a question:

public static void main(String[] args) throws IOException{
			double a,b,c;
				Scanner input = new Scanner(System.in);
				System.out.println("Pass a parameter");
				a = input.nextDouble();
				if(a==0){
					throw new IOException("a parameter can't be equal to 0");
				}
				System.out.println("pass b parameter");
				b = input.nextDouble();
				System.out.println("pass c parameter");
				c = input.nextDouble();
				SquareEq Equation = new SquareEq(a, b, c);
		        if(b==0||c==0){
		        	Equation.halfCount();
		        }
		        else
		        	Equation.fullCount();
        
	}

Is it right to do like this:

public static void main(String[] args) throws IOException

I've already read about throws and it's anounced that throws is used in methods which can't process the exception, but it must be processed in outter try-catch block in which the method with declared throws is executed!
But main is executed by Java runtime!
So this exception will not be processed and we can't write like this?? Am I right??

[gimbal2]

You can wonder about it, or you can test it out. What happens when you trip an IOException, which in your code is as simple as inputting 0?

[Zhenya]

I've already tested it!
when i pass 0 it throws exception:
Exception in thread "main" java.io.IOException: a parameter can't be equal to 0
at newPackage.root.main(root.java:51)

[gimbal2]

Exactly. So. Is that what you want to happen?

[Zhenya]

Exactly. So. Is that what you want to happen?

No, I need explanation!
Here is example from Herbert Schildt

class ThrowsDemo {
  static void throwOne() throws IllegalAccessException {
    System.out.println("Inside throwOne.");
    throw new IllegalAccessException("demo");
  }
  public static void main(String args[]) {
    try {
      throwOne();
    } catch (IllegalAccessException e) {
      System.out.println("Caught " + e);
    }
  }
}

This example is simple and I understand it!
We use

throws

here

static void throwOne() throws IllegalAccessException

because we don't want to handle exception here, we handle it in

public static void main(String args[])

, in which we call this method and it wrapped in

try-catch

block!
So I just want to understand how does java runtime handles exception

 public static void main(String args[]) throws IOException

This method is executed by java runtime!!!
Does java use standard runtime error handler or it's much more complicated?

[JosAH]

When a method 'throws X', it tells the compiler that it might throw an X (but doesn't have to). If your main( ... ) method throws X, and it does so, the JVM (the caller of the main( ... ) method) has to handle that X. The JVM can't and produces a stack trace and terminates.

kind regards,

Jos

[gimbal2]

Does java use standard runtime error handler or it's much more complicated?

What is so complicated about it? It prints the error and quits - that is the behavior you yourself already observed and it cannot be any more simple. What kind of mysteries are you trying to find that aren't there? I have no clue.

[Zhenya]

When a method 'throws X', it tells the compiler that it might throw an X (but doesn't have to). If your main( ... ) method throws X, and it does so, the JVM (the caller of the main( ... ) method) has to handle that X. The JVM can't and produces a stack trace and terminates.

kind regards,

Jos

That's what i need!
Thank you for help!