Unreachability - diff results for diff version

[Geethakrishna Srihari]

For the java version j2sdk1.4.1_06

The statement:
for ( ; false ; );

Gives unreachable error.

but previous versions gives no error...
For exam which is the correct answer? Or how should i approach?

[Srinivasa Raghavan]

Which version of exam are you going to take ?

[Geethakrishna Srihari]

I am taking SCJP 1.4 310-035

[Joyce Lee]

Hi Geethakrishna,

The statement:
for ( ; false ; );

According to JLS2 14.20 Unreachable Statements, that statement is considered unreachable.

for statement can complete normally iff at least one of the following is true:

The for statement is reachable, there is a condition expression, and the condition expression is not a constant expression with value true.

There is a reachable break statement that exits the for statement.

The contained statement is reachable iff the for statement is reachable and the condition expression is not a constant expression whose value is false.

Since you're preparing for SCJP 1.4, I think it's safe as long as we follow the rules specified in JLS 2. So if being asked, I'd choose the one that gives unreachable error as the correct behavior from the compiler. Check out this bug report as well.

If you're preparing for SCJP 5.0, you'll have to refer to JLS 3rd edition.

Joyce
[ June 24, 2005: Message edited by: Joyce Lee ]

[latha yeduguri]

When it is said

for ( ; false ; );

Is it like this you are using false in the place of the i<10 ?

for (int i =0 ;i<10; i++)

[Joyce Lee]

Hi latha,

That's right. The general form of for statement can be expressed as:

for (initialization; conditional expression; iteration expression)

Both false and i<10 are in the conditional expression section. All of these three sections of for statement are optional; that is, the following code is legal:

// this is an endless loop
for ( ; ; )
    System.out.println("Help! Please stop me!");

Joyce
[ June 25, 2005: Message edited by: Joyce Lee ]