每个例外都有必要的试用吗？

Question

A simple question and I can't find the answer for it. Is it required to every exception in Java to use a try-catch? Or is it only for the FileNotFoundException?

A lot of exceptions (IndexOutOfBoundException, ArithmeticException, IlligalArgumentException, NullPointerException) are saying that they didn't need an Exception, but FileNotFoundException does)... and I can't find the answer which do and which doesn't need try-catch.

Answer 1

It's not absolutely required to have a try/catch block for your exceptions. Instead, you can throw them to someone who is able to handle the exception properly.

There are 2 kinds of exceptions: Checked and Unchecked. A Checked exception can be considered one that is found by the compiler, and the compiler knows that it has a chance to occur, so you need to catch or throw it. For example, opening a file. It has a chance to fail, and the compiler knows this, so you're forced to catch or throw the possible IOException .

An Unchecked exception can be considered one that has a chance of occurring, but based on your code, the compiler doesn't know. In other words, it's a programming error . For example, if you're taking user input and expect a number, and the user enters something you didn't expect, such as a string, your program would throw a NumberFormatException . You can predict these scenarios and put try/catch to try and avoid them before they occur. Very rarely seen is a person adding a throws NullPointerException or throws NumberFormatException (or throwing any other Unchecked exception, for that matter). It's allowed, but explicitly creating that exception is weird and most people would say that it's bad coding style.

Note that all Checked suggestions must be caught or thrown to something that can handle it; if you don't do it, your program won't compile. If you throw it to something that can't handle it, then your program will likely crash if it occurs.

Also note that an unchecked Exception (eg: one that occurs during runtime, usually via bad user input or whatnot) will also usually crash your program. Thus, it's usually a good idea to use try/catch when something can potentially go wrong, but you don't have to .

Also interesting to note is that while Checked exceptions are subclasses of Exception and Unchecked exceptions are subclasses of RuntimeException, RuntimeException itself is a subclass of Exception. That means that if you really wanted to, a single try {} catch (Exception e) {} will catch every single exception your program could possibly throw. Granted, this is considered a horrible way to deal with exceptions, and you should catch each one separately so that you can handle them separately. Please try not to use it.

Answer 2

No, not every exception requires a try-catch. Every checked exception requires a try catch. For example, a NullPointerException is an unchecked exception, so it does not require a try-catch, whereas a FileNotFoundException is checked, so it does require one. You can also add "throws" to the method signature and thus avoid needing a try-catch.

Answer 3

Read: https://docs.oracle.com/javase/tutorial/essential/exceptions/

Basically checked Exceptions need to be handled or thrown Unchecked Exceptions and Errors may be handled or thrown (although handling Error is in general considered bad practise).

Checked exception is everything that inherits from java.lang.Exception

Unchecked exception is everything that inherits from java.lang.RuntimeException

Error is everything that inherits from java.lang.Error

Answer 4

只有Checked异常显式需要捕获它，对于其他所有类型的异常，您可以使用“throws”方法签名。

Answer 5

Yes, but if you don't want to handle it in your method you can pass the exception to the caller of the method with the throws keyword. Example:

void execption() throws Exception {
    throw new Exception();
}

void caller() {
    try {
        execption();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

Edit: I'm a bit rusty on my java, like josh said you can have unchecked exceptions that don't need a try/catch like NullPointerException , but you can add one if you think an unchecked exception may be thrown. Example:

Object obj = null;

obj.hashCode();// if you think a NPE will be thrown you can use a try/catch here

Answer 6

When a method that you call explicitly throws an exception then you have to use try....catch loop. But in case of the list you have given are all runtime exceptions. They get thrown when sometimes a program has inputs that were not expected or the program was put to some use that it was not intended for. These would not require a try....catch loop.