how do I reverse a stack?

public Stack reverseStack(final Stack s){

Stack temp = new Stack();

while (! s.empty()){

temp.push(s.pop());

}

return temp;

}

call the method like this

Stack myOriginalStack = new Stack();

// add stuff to your stack

myOriginalStack = reverseStack( myOriginalStack);

Don't forget java forces you to use certain patterns (techniques) that are clearer and easier to debug and modify, that is why there is no true pass by reference in java. It is far better to return a value than to modify it with a pass by reference. The final keyword was added to make sure you don't alter the original copy of the stack (good programming technique).

Message was edited by:

MicroDat

MicroData at 2007-7-10 0:40:58 >

It's a common form to use void signatures if the argument is mutated.

Stack extends Vector so is O(1) access, so you can swap the first and last elements, then the second and first from last, and so on until you have reversed the whole Vector:

[0,1,2,3,4]

[4,1,2,3,0]

[4,3,2,1,0]

Pete

pm_kirkhama at 2007-7-10 0:40:58 >

one more thing I cant use vector because I haven't learned it. The only thing I can do is by creating a new stack and using the pop and push method. But as I posted on my very first post it fails somehow to get s reference to temp at the end. This is the only problem. I also tried to use s.addAll(temp) but somehow it wont give me the reversed stack

aditya15417a at 2007-7-10 0:40:59 >

> so there's no other way to do this except if I make

> my own stack class not using the java.util.Stack?

If you can't make use of the java.util.Vector class, then you cannot use the java.util.Stack class since a java.util.Stack IS a java.util.Vector. In that case, you'll need to write your own Stack class.

Do you understand what it means that the java.util.Stack class extends the java.util.Vector class?

prometheuzza at 2007-7-21 17:54:26 >

Here's the inheretance tree of the java.util.Stack class:

java.lang.Object

|

+--> java.util.AbstractCollection

|

+--> java.util.AbstractList

|

+--> java.util.Vector

|

+--> java.util.Stackso a Stack is an Object, an AbstractCollection, an AbstractList and a Vector. All the methods defined in those classes can be used by the Stack class. So again, if your teacher says you cannot make use of the java.util.Vector class, then you cannot make use of the java.util.Stack class.

prometheuzza at 2007-7-21 17:54:26 >

so here's my code, but still won't work:

Stack<Object> temp = new Stack<Object>();

Stack<Object> temp2 = new Stack<Object>();

int count = 0;

while (!s.empty()){

temp.push(s.pop());

count++;

}

for (int i = count; i>=0 ; i--){

temp2.push(temp.pop());

}

while(!temp2.empty()){

s.push(temp2.pop());

aditya15417a at 2007-7-21 17:54:26 >

> so here's my code, but still won't work:

>

> ...

Now we can all go and play outside:import java.util.Stack;

public class StackTrouble {

public <T> void reverseStack(Stack<T> s){

Stack<T> temp = new Stack<T>();

temp.addAll(s);

s.clear();

while(!temp.isEmpty()) {

s.push(temp.pop());

}

}

public static void main(String[] args) {

StackTrouble st = new StackTrouble();

Stack<String> stack = new Stack<String>();

stack.push("A");

stack.push("B");

stack.push("C");

System.out.println("Before : "+stack);

st.reverseStack(stack);

System.out.println("After : "+stack);

}

}

prometheuzza at 2007-7-21 17:54:26 >