Adapter - Structural Design Pattern

public interface Stack {
    public void push(int x);
    public void pop();
    public int top();
    boolean empty();
}
public class FixedArray {
    public FixedArray() {
    index = -1;
    items = new int[10];
    }
    public void insert(int x) { items[++index] = x; }
    public void removeLast() { --index; }
    public boolean empty() { return index == -1; }
    public int top() { return items[index]; }
    private int index;
    private int [] items;
}
// making FixedArray used in Stack
public class ArrayStack implements Stack {
    private FixedArray array;
    public ArrayStack() { array = new FixedArray(); }
    public void push(int x) { array.insert(x); }
    public void pop() { array.removeLast(); }
    public int top() { return array.top(); }
    public boolean empty() { return array.empty(); }
}