当一起处理和声明异常时会发生什么？

Question

I'm sitting for the 1z0-808 exam and many questions about exception handling appear with "throws" and a "try-catch" block used together.

I would like to know how does "throws" affect the output of a "try-catch" block when they are used together.

My understanding so far is that:

1. "try-catch" block will handle exceptions and execute any code that you define in the "catch" block.

2. "throws" declares an exception and will shift the exception handling responsibility up the stack. For example:

    public class Test{ static void test() throws Exception{ throw new Exception(); } public static void main(String[] args) throws Exception{ test(); // A stack trace is printed } } 

3. Using "try-catch" and "throws". For example:

    public class Test{ static void test() throws Exception{ try{ throw new Exception(); } catch(Exception e){ System.out.println("Handling is done"); } } public static void main(String[] args) throws Exception{ test(); // Outputs: "Handling is done" } } 

   Is there any purpose or effect in using "throws" if the exception is handled by the "try-catch" block?

Answer 1

Is there any purpose or effect in using "throws" if the exception is handled by the "try-catch" block?

Yes it is.

I can catch a default Exception thrown from Java for ex IllegalArgumentException and I can re throw some meaningful custom exception.

So it is meaningful when you re throw exception from catch block with more details.

public void doLogin() throws NiceUserException {
    try {
        //To Do
    } catch(IllegalArgumentException e) {
        throw new NiceUserException("Hey! You forgot to pass your username");
    }
}