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 t

Answer 1

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;
    }
}

Answer 2

You can use LinkedHashMap and override its removeEldestEntry method:

public class FixedStack extends LinkedHashMap<Long, String> {

    private final int capacity;

    public FixedStack(int capacity) {
        this.capacity = capacity;
    }

    @Override
    protected boolean removeEldestEntry(final Map.Entry<Long, String> eldest) {
        return super.size() > capacity;
    }
}

And to test it:

    public static void main(String[] args) {

        FixedStack stack = new FixedStack(10);

        long added = 0;
        for (Locale locale : Locale.getAvailableLocales()) {
            if (locale.getDisplayCountry().length() > 0) {
                stack.put(added, locale.getDisplayCountry());
                System.out.println(locale.getDisplayCountry());
                added++;
            }
        }
        System.out.println(String.format(">>>>>>>>> %s added",
                added));
        Iterator<Entry<Long, String>> iterator = stack.entrySet().iterator();
        while (iterator.hasNext()) {
            System.out.println(iterator.next().getValue());
        }
    }

You just have to decide what you want to use as the key, I used a simple counter in the example.