stack lifo

[oll3i]

@Override
public IAbstractQueryResult pop () { return lifo.pop();
}

In main

IAbstractQueryResult resLeft = qres.pop()

here i get empty stack exception

Thank YOU

[r035198x]

You are trying to get an element from an empty stack.

Either your logic is wrong and pop is being called when it's not supposed to be called or you should check to see if there is an element before popping.

[oll3i]

QResStack qres = new QResStack();
qres.push(new IntegerResult(1)); // (1)
qres.push(new IntegerResult(2)); // (2)
{ // (3)
IAbstractQueryResult resRight = qres.pop();
IAbstractQueryResult resLeft = qres.pop();
//iloczyn kartezjanski - operator przecinka
IBagResult commaRes = QExecUtils.cartesianProduct(resLeft,resRight);
qres.push(commaRes);
}
qres.push(new IntegerResult(3)); // (4)
qres.push(new IntegerResult(4)); // (5)
{ // (6)
IntegerResult resRight = (IntegerResult) qres.pop();
IntegerResult resLeft = (IntegerResult) qres.pop();
IntegerResult plusRes = new IntegerResult((Integer)resLeft.getValue() + (Integer)resRight.getValue());
qres.push(plusRes);
}
{ // (7)
IAbstractQueryResult resRight = qres.pop();
IAbstractQueryResult resLeft = qres.pop();

at the last line i get
run:
Exception in thread "main" java.util.Empty StackException
at java.util.Stack .peek(Stack.jav a:102)
at java.util.Stack .pop(Stack.java :84)
at s4409_s4409_pr2 .QResStack.pop( QResStack.java: 20)
at s4409_s4409_pr2 .S4409_s4409_pr 2.main(S4409_s4 409_pr2.java:51 )
Java Result: 1

[Nepomuk]

Without knowing the exact implementation of your stack it's difficult to tell; I implemented a simple stack, used it with your code and it works fine. Maybe debug the QResStack function? It seems that whatever internal data collection you're using there's no element in it at the last line.