Java Declaring a variable in an if-statement

Question

I had a fellow student ask me this question and I have no idea how to answer it.

The following code works fine.

    int x = 40;
    int y = 35;
    if (x > y)
    {
        int ans = x + y;
    }

However, the code below gives an error saying that the variable declaration isn't allowed where it is. Why isn't it allowed there? NetBeans throws the following exception: Uncompilable source code - Erroneous tree type:

    int x = 40;
    int y = 35;
    if (x > y)
        int ans = x + y;

We are using NetBeans 8.0 Beta if it matters.

NetBeans compiles the top code correctly and the bottom one tells me that variable declaration is not allowed there. I am wondering why it is not allowed. Thanks for the quick response! — user3806867, Jul 05 '14 at 02:38
Its not clear how it would not work with the information you've provided. Both will compile — Amir Afghani, Jul 05 '14 at 02:38
On the bottom code NetBeans throws an exception: Uncompilable source code - Erroneous tree type: — user3806867, Jul 05 '14 at 02:41
That information should be part of your question as it is key to understanding your problem. — Hovercraft Full Of Eels, Jul 05 '14 at 02:45

score 1 · Answer 1 · answered Jul 05 '14 at 02:37

1

Not so much a question of working or not working, it's a syntax error. You can't have variable declarations outside of a block.

Why would you even want to do the second pattern? Who is going to use ans?

answered Jul 05 '14 at 02:37

Thilo

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Define "*outside of a block*" – PM 77-1 Jul 05 '14 at 02:42

score 1 · Accepted Answer · answered Jul 05 '14 at 02:39

When you scope a variable, it will only be available in that scope.

if (stuff) {
    int i;
    // i available here
}
// i not available here

The first type, the compiler doesn't know if you will use the variable later. it doesn't think there's anything wrong with creating a variable in that block.

In the second type, the compiler knows there is only one statement, because you didn't create a {} block. The variable that you created will definitely not be used, so the compiler is alerting you that you will never be able to use the variable that you defined there.

Because it's not in a block it would automatically be out of scope so it's useless. I understand now. — user3806867, Jul 05 '14 at 03:02

Java Declaring a variable in an if-statement

2 Answers2