CODEWITHSUNDEEP
javaexception
Ruchira Gayan Ranaweera
Ruchira Gayan Ranaweera

Reputation: 35597

Why can't use throws Exception here?

Consider following statement

BufferedReader br=new BufferedReader(new FileReader("D:\\test.txt"));

Normally we have to throws Exception or we have to use try-catch to handle the Exception.

But if I want to use this in a static block as follows. Only thing can do is use try-catch block to handle the Exception. But can't use throws here? What is the reason behind java doesn't provide throws here?

  static {
    try {
        BufferedReader br = new BufferedReader(new FileReader("D:\\test.txt"));
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    }
  }

Let me add this too. The case the block not a static block similar rule apply here.

 {
    try {
        BufferedReader br = new BufferedReader(new FileReader("D:\\test.txt"));
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    }
}

We can normally do if this in a method as follows

    public static void main(String[] args) throws FileNotFoundException {
    BufferedReader br = new BufferedReader(new FileReader("D:\\test.txt"));
     }

Upvotes: 0

Views: 315

Answers (4)

René Jensen
René Jensen

Reputation: 451

It's a static block being run when the class is initialized. Since it's a checked exception, you cannot throw it as there's nowhere to catch it.
throwing an unchecked exception is possible, but it will crash the program, as neither that can be caught anywhere.

Instead, you can put the code in a

public static void init() throws FileNotFoundException
{
   BufferedReader br = new BufferedReader(new FileReader("D:\\test.txt"));
}

And then call that once on your program start up.

Edit: Removing the static keyword doesn't change anything in the compiled result. It's just the syntax that allows it to be missing.

Upvotes: 6

Evgeniy Dorofeev
Evgeniy Dorofeev

Reputation: 136152

You can throw an exception from init block but it should be an unchecked exception. What you can do is this

static {
    try {
        BufferedReader br = new BufferedReader(new FileReader("D:\\test.txt"));
    } catch (FileNotFoundException e) {
        throw new IllegalStateException(e);
    }
}

Upvotes: 0

vikingsteve
vikingsteve

Reputation: 40438

Since an exception escaping the static block would cause an ExceptionInInitializerError.

In other words, don't let Exceptions escape from a static initializer - handle them instead.

Upvotes: 0

kajacx
kajacx

Reputation: 12959

Well, static code block like that is run when your class is loaded (ussualy after JVM starts), so throwing exeption here would crush your entire java program, as you cant catch it anywhere

Upvotes: 0

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