Creating a fixed-size Stack

Question

I want to create a Stack in Java, but fix the size. For example, create a new Stack, set the size to 10, then as I push items to the stack it fills up and when it fills up to ten, the last item in the stack is pushed off (removed). I want to use Stack because it uses LIFO and fits my needs very well.

But the setSize() method that Stack inherits from Vector doesn't seem to actually limit the size of the Stack. I think I am missing something about how Stacks work, or maybe Stacks weren't meant to be constrained so it is impossible. Please educate me!

Answer 1

Here is a SizedStack type that extends Stack:

import java.util.Stack;  public class SizedStack<T> extends Stack<T> {     private int maxSize;      public SizedStack(int size) {         super();         this.maxSize = size;     }      @Override     public T push(T object) {         //If the stack is too big, remove elements until it's the right size.         while (this.size() >= maxSize) {             this.remove(0);         }         return super.push(object);     } } 

Use it like this: Stack<Double> mySizedStack = new SizedStack<Double>(10);. Other than the size, it operates like any other Stack.

Answer 2

You can create a very simple stack like this:

public class FixedStack<T> {     private T[] stack;     private int size;     private int top;      public FixedStack<T>(int size)     {         this.stack = (T[]) new Object[size];         this.top = -1;         this.size = size;     }      public void push(T obj)     {         if (top >= size)             throw new IndexOutOfBoundsException("Stack size = " + size);         stack[++top] = obj;     }      public T pop()     {         if (top < 0) throw new IndexOutOfBoundsException();         T obj = stack[top--];         stack[top + 1] = null;         return obj;     }      public int size()     {         return size;     }      public int elements()     {         return top + 1;     } }