What's the difference between these two java code? [duplicate]

Question

if without the throws IllegalArgumentException, I can still throw exception that catched by the catch block in the main fucntion, why I need throws IllegalArgumentException??

public class ExceptionsTest { public static void funcThrowsException(int n) throws IllegalArgumentException{ if(n == 0){ throw new IllegalArgumentException("ex"); } } public static void main(String[] args) { try{ funcThrowsException(0); }catch (IllegalArgumentException e){ System.out.println(e.getMessage()); } } }

public class ExceptionsTest { public static void funcThrowsException(int n){ if(n == 0){ throw new IllegalArgumentException("ex"); } } public static void main(String[] args) { try{ funcThrowsException(0); }catch (IllegalArgumentException e){ System.out.println(e.getMessage()); } } }

Their output are same:

ex Process finished with exit code 0

I don't know why we need throws keywords

depending on the type of Exception, throws is (or isn't) mandatory. IllegalArgumentException is a subclass of RuntimeException, and for RuntimeException, it is not required to put 'throws' in the method signature. For non-RuntimeException Exceptions, it is required. — Stultuske
– Stultuske, Commented Mar 16, 2023 at 10:18

Jon Skeet · Accepted Answer · 2023-03-16 10:19:24Z

4

I don't know why we need throws keywords

In this case, you don't - because IllegalArgumentException extends RuntimeException. It's therefore not a checked exception, and doesn't need to be declared in a method that throws it.

See the Java tutorial for more details on when you need to use a throws declaration.

answered Mar 16, 2023 at 10:19

Jon Skeet

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2 Comments

miao sun Over a year ago

Thank you, When a checked exception is thrown, only callers who can handle it properly should catch it with a try/catch. A runtime exception, should not be caught in the program. If you catch it, you run the risk that a bug in the code will be hidden from view at runtime. Is my understanding right?

Jon Skeet Over a year ago

@miaosun: Not necessarily - you certainly can catch RuntimeExceptions, and sometimes that's appropriate... but it's less common.

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