Tricky stuff

[JosAH]

As everybody knows (or should know) the following is useless:

[code=java]
private static int x= 42;
...
x= x++;
[/code]
The value of x will stay 42. Or does it? Have a look at the following little experiment
and try to figure out what is happening:

[code=java]
public class TrickyStuff {

private static int x= 42;

public static void main(String[] args) {

(new Thread() {
public void run() {
while(x == 42);
System.out.prin tln( "x != 42" );
System.exit(0);
}
} ).start();

System.out.prin tln("x= "+x);
while(true) { x=x++;}
}
}[/code]

kind regards,

Jos

[prometheuzz]

It's because 42 is a special kind of integer, of course!
; )

Here's another one:

[CODE=java]public class TrickyStuff {

public static void main(String[] args) {

double a = 0.1 + 0.1 + 0.1 + 0.1 + 0.1 + 0.1 + 0.1 + 0.1;
double b = 0.8;

System.out.prin tln("Are a and b the same? "+(a==b));
}
}[/CODE]
The output is "Are a and b the same? false". How is this possible?
It's not for you Jos: I know you know the answer.

[JosAH]

It's not for you Jos: I know you know the answer.

I don't want to participate in any contest that wants me to participate :-P

kind regards,

Jos (duh ;-)

[Tripmaker]

It's because 42 is a special kind of integer, of course!
; )

Here's another one:

[CODE=java]public class TrickyStuff {

public static void main(String[] args) {

double a = 0.1 + 0.1 + 0.1 + 0.1 + 0.1 + 0.1 + 0.1 + 0.1;
double b = 0.8;

System.out.prin tln("Are a and b the same? "+(a==b));
}
}[/CODE]
The output is "Are a and b the same? false". How is this possible?
It's not for you Jos: I know you know the answer.

I'm new at programming so I'm going to take a calculated guess. The answer for a = 0.7999999999999 999 . The reason being double belongs to Floating-point numbers which represent numbers with fractional precision. Double doesn't round off a number.

Petra

[JosAH]

I'm new at programming so I'm going to take a calculated guess. The answer for a = 0.7999999999999 999 . The reason being double belongs to Floating-point numbers which represent numbers with fractional precision. Double doesn't round off a number.

Petra

Very close; bookmark this document and read it when you find some spare time.

kind regards,

Jos

ps. now what about that x == 42 thingie in my original post?

[sumittyagi]

As everybody knows (or should know) the following is useless:

[code=java]
private static int x= 42;
...
x= x++;
[/code]
The value of x will stay 42. Or does it? Have a look at the following little experiment
and try to figure out what is happening:

[code=java]
public class TrickyStuff {

private static int x= 42;

public static void main(String[] args) {

(new Thread() {
public void run() {
while(x == 42);
System.out.prin tln( "x != 42" );
System.exit(0);
}
} ).start();

System.out.prin tln("x= "+x);
while(true) { x=x++;}
}
}[/code]

kind regards,

Jos

Why is it useless?
x is not declared final, and thus is not a constant.

It's because 42 is a special kind of integer, of course!
; )

I didn't get this line. It would be great if you could explain this one.
Thanks!

Regards,
Sumit Tyagi.

[JosAH]

Why is it useless?
x is not declared final, and thus is not a constant.

So you're not surprised by the output it shows?

I didn't get this line. It would be great if you could explain this one.
Thanks!

42 is 54 using base 13.

kind regards,

Jos

[r035198x]

Why is it useless?
x is not declared final, and thus is not a constant.



I didn't get this line. It would be great if you could explain this one.
Thanks!

Regards,
Sumit Tyagi.

It's not a constant alright but when you do
[CODE=java]while(true) {
x = x++;
}[/CODE]
the value of x does not change since x will be assigned to the previous value always which will be the initial value. The post increment won't take any effect there. But when a thread is reading off the values of x ...

[Tripmaker]

As everybody knows (or should know) the following is useless:

[code=java]
private static int x= 42;
...
x= x++;
[/code]
The value of x will stay 42. Or does it? Have a look at the following little experiment
and try to figure out what is happening:

[code=java]
public class TrickyStuff {

private static int x= 42;

public static void main(String[] args) {

(new Thread() {
public void run() {
while(x == 42);
System.out.prin tln( "x != 42" );
System.exit(0);
}
} ).start();

System.out.prin tln("x= "+x);
while(true) { x=x++;}
}
}[/code]

kind regards,

Jos

Let see if I can get this right. The value stays at 42 because of the while statement. In laymans terms while x == 42 the system prints out x != 42 and the program is ended. Everytime you re-run the program you keep getting the same answer. You will never get to the second while statement.

[r035198x]

Let see if I can get this right. The value stays at 42 because of the while statement. In laymans terms while x == 42 the system prints out x != 42 and the program is ended. Everytime you re-run the program you keep getting the same answer. You will never get to the second while statement.

Put the program on your compiler and test it. Realize also that there are two threads running here.

[sumittyagi]

So you're not surprised by the output it shows?

Yea! I am not surprized by the output, because output is as I expected it to be.
---------- java ----------
x= 42
x != 42
Normal Termination
Output completed (1 sec consumed).

42 is 54 using base 13.

But how does that make a difference. I mean does this fact have any influence on the output.

[r035198x]

Yea! I am not surprized by the output, because output is as I expected it to be.
...

Would you then care to explain why the value of x changes (or seems to change)?

[sumittyagi]

It's not a constant alright but when you do
[CODE=java]while(true) {
x = x++;
}[/CODE]
the value of x does not change since x will be assigned to the previous value always which will be the initial value. The post increment won't take any effect there. But when a thread is reading off the values of x ...

x++ is having a side effect of incrementing the value of x.
so it will be solved as follows:
x = x++;
x = 42 (value replaced, so x becomes 42);
x++ (x++ have side effect of incrementing x, so now x becomes 43);

[prometheuzz]

Yea! I am not surprized by the output, because output is as I expected it to be.
---------- java ----------
x= 42
x != 42
Normal Termination
Output completed (1 sec consumed).

Huh? Have we compiled and run the same code (from the original post)? I don't get that output!

But how does that make a difference. I mean does this fact have any influence on the output.

That was a joke of me (42 being a special kind of integer).

[sumittyagi]

Huh? Have we compiled and run the same code (from the original post)? I don't get that output!

Then what output are u getting?

That was a joke of me (42 being a special kind of integer).

There are a lots of things in java that make you bite your finger, so I never take any statement as joke.

But that was nice one!!! LOL.