newbie: getKeyStates()

[Jeff]

Hey

midp 2.0
J2ME Wireless Toolkit 2.2
JDK 5


I get an NullPointerException when running the code (copy of code added
below, data output also added under the code), and I don't know what is
causing this exception... If you see what I'm doing wrong here, then please
tell me

public void checkKeys() {
int keyState = getKeyStates();
System.out.println(keyState);
if ((keyState & LEFT_PRESSED) != 0) {
System.out.println("LEFT_PRESSED");
}
}
***************************
Here is the thread code, you see that checkKeys are called in the loop
public void run() {
testCanvas.flushKeys();
testPause = false;
testStop = false;
while (true) {
if (testStop) {
break;
}
while (testPause) {
synchronized(this) {
try {
wait();
}
catch (Exception e) {
}
}
synchronized(this) {
try {
wait(1);
}
catch(Exception e) {}
}
}
testCanvas.checkKeys();
testCanvas.advance();
}
}

The output from this code is (as you can see from the output that this
output contain data from more than one iteraton):
I did click only 1 time on LEFT_PRESSED (on emulator) and it looks like the
loop are processing my click several times (getKeyStates= 4, 4, 0, 0):
4
LEFT_PRESSED
java.lang.NullPointerException
4
LEFT_PRESSED
java.lang.NullPointerException
0
0
0
-1
LEFT_PRESSED
java.lang.NullPointerException
-1
LEFT_PRESSED
java.lang.NullPointerException
-1
LEFT_PRESSED
java.lang.NullPointerException

I'm very thankful for help on this issue!

Jeff

 

[zero]

Hey

midp 2.0
J2ME Wireless Toolkit 2.2
JDK 5


I get an NullPointerException when running the code (copy of code
added below, data output also added under the code), and I don't know
what is causing this exception... If you see what I'm doing wrong
here, then please tell me

public void checkKeys() {
int keyState = getKeyStates();

what does getKeyStates do?

System.out.println(keyState);
if ((keyState & LEFT_PRESSED) != 0) {

how is LEFT_PRESSED defined?

System.out.println("LEFT_PRESSED");
}
}
***************************
Here is the thread code, you see that checkKeys are called in the loop
public void run() {
testCanvas.flushKeys();

what is testCanvas? What does flushKeys do?

testPause = false;
testStop = false;
while (true) {
if (testStop) {
break;
}

unless you have a very good reason, while(true) and break; are usually
not a good idea.

while(!testStop)
{
// ...
}

while (testPause) {
synchronized(this) {
try {
wait();
}
catch (Exception e) {
}

please don't drop exceptions like this. Especially not *all* exceptions,
as you are doing here.

catch(InterruptedException e)
{
// ...
}

}
synchronized(this) {
try {
wait(1);
}
catch(Exception e) {}

see above

}
}

a better, consistent indentation style will make your code much easier to
read and maintain.

testCanvas.checkKeys();
testCanvas.advance();

what does advance do?

}
}

The output from this code is (as you can see from the output that this
output contain data from more than one iteraton):
I did click only 1 time on LEFT_PRESSED (on emulator) and it looks
like the loop are processing my click several times

why is there a loop anyway? How does testStop ever get set to true? In
this code snippet it doesn't.

(getKeyStates= 4,
4, 0, 0): 4
LEFT_PRESSED
java.lang.NullPointerException
4
LEFT_PRESSED
java.lang.NullPointerException
0
0
0
-1
LEFT_PRESSED
java.lang.NullPointerException
-1
LEFT_PRESSED
java.lang.NullPointerException
-1
LEFT_PRESSED
java.lang.NullPointerException

It looks like you're catching this exception somewhere, and then only
printing its name. If you use ExceptionrintStackTrace() you'll see the
exact line number that causes the exception. For a NullPointerException
it's very easy once you know what line throws the exception: it means one
of the objects on that line is null - most likely because it was never
instatiated.

From this code snippet there is no way to tell what is going wrong
exactly. I suggest you look at the notes above, and after correcting
them post a more complete (but short!) example - if you haven't found the
solution yourself yet.

 

[Jeff]

Thank you for the tip about ExceptionrintStackTrace() , it took me 5
minutes to fix this problem

Jeff