Question

Need serious help here...

Answer 1

What's your question?

Answer 2

Well, I need to know how to add an array list to this

import java.util.*;

public class StackHW
{
public static void main(String args[])
{
// Create a new, empty stack
Stack<String> stack1 = new Stack<String>();

stack1.push("Frist (bottom)");
printStack(stack1);


stack1.push("Second (middle)");
printStack(stack1);


stack1.push("Third (top)");
printStack(stack1);


stack1.pop();
printStack(stack1);


stack1.pop();
printStack(stack1);

stack1.pop();
printStack(stack1);

}


public static void printStack(Stack<String> s)
{
if (s.isEmpty())
System.out.println("You have nothing in your stack");
else
System.out.printf("%s TOP\n", s);
}

}

Answer 3

http://stackoverflow.com/questions/1200621/how-to-declare-an-array-in-java

Answer 4

This is an example of how to declare an arraylist:

ArrayList<String> arrayList = new ArrayList<String>();

Answer 5

Okay, got that.

Answer 6

okay, now you have to make the arraylist behave like a stack. In a stack, everything is First In First Out, so anytime you "push" something to it, it goes behind everything that was there before. basically like how you form a line to see a movie or something. make sense?

Answer 7

ArrayList<String> aList = new ArrayList<String>(5);
aList.add("One(bottom)");
aList.add("Two");
aList.add("Third");
aList.add("Fourth");
aList.add("First(Top)");

System.out.println(aList);

Answer 8

Stack<String> stack1 = new Stack<String>();

stack1.push(?);

Answer 9

I described stack wrong -- I was thinking of a queue. A stack is Last In First Out.

Answer 10

but what is your question now?

Answer 11

how can I add an array value to the statement > stack1.push(?);

Answer 12

aList[1]?

Answer 13

stack1.push(aList[1]); ?

Answer 14

stack1.push(aList[1]);

will grab the value at aList[1] ("Two" in this case), and push that value to the stack

Is that what you want?

Answer 15

Yes, but I'm getting an error.

Answer 16

what does it say

Answer 17

Error(39, 26) java: array required, but java.util.ArrayList<java.lang.String> Found

Answer 18

when you declared your arraylist, you put

ArrayList<String> aList = new ArrayList<String>(5);

The (5) is not necessary, just try ()

Answer 19

the arraylist will grow dynamically and you dont need to set its size

Answer 20

ah, i see the problem

Answer 21

stack1.push(aList.get(1));

is the command you need

Answer 22

aList.get(2)

Answer 23

Yes, that seems to work.

Answer 24

cool

Answer 25

Nice, thanks! Now all I need is to add top() to retrieve element...

Answer 26

top will retrieve the last element inserted into the stack

Answer 27

so, this is the last element in the arraylist. any idea how to get this index?

Answer 28

Nope.

stack1.top();?

Answer 29

aList.size() will give you the total number of elements in the arraylist. how can we use this number to get the index of the last element in the arraylist?

Answer 30

aList.size()-1

Answer 31

?

Answer 32

perfect

Answer 33

But now I gotta create my own Stack class :/ >
Do NOT use the predefined java Stack class, and create your own Stack.java instead.

Answer 34

That's what it sounds like to me..

Answer 35

can you still use an arraylist?

Answer 36

Yeah

Answer 37

Do you know about private instance variables?

Answer 38

Somewhat

Answer 39

You will need one to keep track of the arraylist as you modify it (add, remove, etc)

import java.util.*;

public class StackHW {

private ArrayList<String> aList = ArrayList<String>();

public void push(String element) {

//use the arraylist to add the element (you did this already in the previous example)

}
public static void main(String[] args) {

StackHW myStack = new StackHW();

mystack.push("Hello");

}

}

Can you make push work? It's just one line of code.

Answer 40

you might need to put static after private, but I'm not sure.

Answer 41

Okay, I'm not sure if I got the top() method to work for me.

public Object top() throws StackEmptyException
{
if(stack1.isEmpty())
throw new StackEmptyException("Stack is empty.") ;
return ? ;
}

Answer 42

without using an arraylist?