Problem with return statement....

[Justin Fox]

    
public class Stack<T>
{
public int count = 0, size = 0, top = -1;
public String result;
public T[] array;
 
int front = 0;
 
public Stack(int number)
{
array = (T[])new Object[number];
}
 
public void push(T obj)
{
if(isNotFull())
{
top++;
array[top] = obj;
}
 

}
 

public T pop()
{
    if( isNotEmpty() )
        return array[top--];
 

}
 

public boolean isNotFull()
{
return top<array.length-1;
}
 
public boolean isNotEmpty()
{
return top >= 0;
}
 

 
public void dump()
{
 
System.out.print("\t\t\t top: " + top + " Contents: " );
 front = top;
 
while(front>=0)
System.out.print(array[front--] + " ");
 
System.out.println();
 
}
 
public int Size()
{
return top+1;
}
 

}
 

ok in the code above, im having a problem with the pop() method...

    
public T pop()
{
    if( isNotEmpty() )
        return array[top--];
 

}
 

i have a return statement, so why is the compiler telling me im

missing it??

Justin

[Christophe Verré]

Hint: When the array is empty, are you returning anything ?

[Justin Fox]

well i cant return -1 or 0, cause is has to be of type T

and the stack class doesnt know what thats going to be yet..


I'm pretty much lost here...

Justin

[Dana Bothner-By]

Ask yourself: what should be the result of popping an empty stack? What's the first thing that comes to mind?

[Justin Fox]

an error message, but i added that, and it still gave me

a missing return statement error..

i had a throw new IndexOutOfBoundsException(-1);

but it threw it every time it called it....

Justin
[ August 29, 2006: Message edited by: Justin Fox ]

[Chetan Raju]

public T pop()
{
    if( isNotEmpty() )
        return array[top--];
 

}

You can see that the return statement is a part of the if block. What if the if block doesn't execute (ie if isNotEmpty() returns false). Then there is no return statement executed in the method.

[Muhammad Saifuddin]

public T pop()
{
    if( isNotEmpty() )
        return array[top--];
 
}    

Look you are not returning anything in the pop method block.
while you are using a return statement in a if condition, it is in
scope of if statement not in method block.

[Justin Fox]

dude, i know that...

what am i supposed to return?

if i just throw a

return array[top];

in there...

ill eventually get a boundsexception

and my application will terminate...

and if i remove the if loop, same thing...

thats what i need to know...

what should i put....

or point me in some kind of direction...

dont tell me what i already know...

thanks,

Justin

[Christophe Verré]

You should do the other way around. Not checking if it's not empty, but checking if it's empty.

If it's empty, throw something (not your keyboard), like java.util.EmptyStackException.

If it's not empty, pop blop wiiiiz

[Rusty Shackleford]

Originally posted by Justin Fox:
dude, i know that...

what am i supposed to return?

if i just throw a

return array[top];

in there...

ill eventually get a boundsexception

and my application will terminate...

and if i remove the if loop, same thing...

thats what i need to know...

what should i put....

or point me in some kind of direction...

dont tell me what i already know...

thanks,

Justin

Why are you being rude?

You obviously didn't know because you were asking why the compiler was complaining about no return statement.

As was noted, your design needs to be rethought.

[Ilja Preuss]

Originally posted by Justin Fox:

i had a throw new IndexOutOfBoundsException(-1);

but it threw it every time it called it....

Then you were on the right track, but did something wrong. What did your code look like?