Gui calling method

[Dustin Schreader]

I'm trying to call this method

	public void push(T newElement)	
	{
		StackNode<T> current = stackTop;
		StackNode<T> previous = null;
		
		super.push(newElement);
		count++;
		if (count > size)
			{
				while (current != null)
				{
				previous = current;
				current = current.link;
				}
			previous.link = null;	
			count--;
			}
	}

from dropoutstack class
and this is how I do it in my gui class

	private class PushButtonHandler implements ActionListener
	{
		public void actionPerformed(ActionEvent e)
		{
			
			DropOutStack myStack = new DropOutStack();
			myStack.push(newElement);
		}
	}

but i'm getting this error

GuiDropOutStack.java:100: cannot find symbol
symbol  : variable newElement
location: class GuiDropOutStack.PushButtonHandler
			myStack.push(newElement);

I'm still having a hard time understanding this OOP why doesn't this find newElement?

[Christophe Verré]

Where did you declare newElement ?

[Dustin Schreader]

ok I didn't declare newElement, so I'm assuming that whenever there are parameters you must declare them then. It's type T so how would I declare that?

[Mohamed Sanaulla]

Dustin Schreader wrote:ok I didn't declare newElement, so I'm assuming that whenever there are parameters you must declare them then. It's type T so how would I declare that?

Yes, you would have to declare any variable being used in the code. As far as the type T is concerned, it would work as follows-

So if your newElement is of type- String, then T would be String. Implicitly this type information will be passed to the method you are invoking.
Actually the type T would depend on the type information being provided while creating the instance of the class. Can you provide us the DropOutStack class definition?

[Dustin Schreader]

public class DropOutStack<T> extends LinkedStackClass<T>
{
	int size;
	int count = 0;
	
	public DropOutStack()
	{
		super();
	}
	
	public void push(T newElement)	
	{
		StackNode<T> current = stackTop;
		StackNode<T> previous = null;
		
		super.push(newElement);
		count++;
		if (count > size)
			{
				while (current != null)
				{
				previous = current;
				current = current.link;
				}
			previous.link = null;	
			count--;
			}
	}		
	
	public void pop() throws StackUnderflowException
	{
		super.pop();
		count--;
	}
	
	public void setSize(int size)
	{
		if (size > 0)
			this.size = size;
			else
			throw new NumberFormatException("dropout size invalid");
	}
}

[Mohamed Sanaulla]

So when you are creating the instance of DropOutStack, you should be using this:

DropOutStack<String> myStack = new DropOutStack<String>(); 
/*
String can be replaced by any type you would want the stack 
to contain. So all the other method would expect data of the 
above type. 
*/

Also please check the pop() method- it isnt returning anything?

[Dustin Schreader]

I think I added the DropOutStack<String> myStack = new DropOutStack<String>(); to the method already but I guess I need to declare newElement so How do I do that?

In my DropOutStack class I was just overriding the pop method from my linked stack class.

[Mohamed Sanaulla]

Dustin Schreader wrote:I think I added the DropOutStack<String> myStack = new DropOutStack<String>(); to the method already but I guess I need to declare newElement so How do I do that?

In my DropOutStack class I was just overriding the pop method from my linked stack class.

The newElement can be declared as-

String newElement = "This should be the input from the user" ;
//The value for the above element would be from the user input-
//might be from the GUI component- Textbox? 

And also check the pop method defined in LinkedStackClass- pretty strange that it doesnt return the popped value. You might want to explore the Collection classes from the Java library.