สร้าง Stack รับ Generic Type

แบบง่ายๆ นะครับ

import java.lang.reflect.Array;

 class Stack<T> {

    private final T[] array;
    public int index = -1;
    public Stack(Class<T> tClass, int stackSize) {
        array = (T[]) Array.newInstance(tClass, stackSize);
    }

    public void push(T t) {
        array[++index] = t;
    }

    private T pop() throws Exception {
        if (index < 0) {
            throw new Exception("Stack is empty.");
        }
        return array[index--];
    }

     public static void main(String[] args) throws Exception {
         Stack<String> stringStack = new Stack<String>(String.class, 50);
         stringStack.push("Hello");
         stringStack.push("Pee");
         stringStack.push("Nok");
         stringStack.push("Bee");
         System.out.println(stringStack.index);
         System.out.println(stringStack.pop());
         System.out.println(stringStack.pop());
         System.out.println(stringStack.pop());
         System.out.println(stringStack.pop());
         System.out.println(stringStack.pop());
         System.out.println(stringStack.pop());
     }
}

ผลที่ได้

อีกแบบใช้ List แทน Array นะครับ

import java.util.ArrayList;
import java.util.List;

class Stack<T> {

     private List<T> mylist = new ArrayList<>();

    public void add(T t) {
         mylist.add(t);
    }

    private T get() throws Exception {
        if (mylist.isEmpty()) {
            return null;
        }
        final int index = mylist.size() - 1;
        T t = mylist.get(index);
        mylist.remove(index);
        return t;
    }

     public static void main(String[] args) throws Exception {
         Stack<Integer> stack = new Stack<>();
         stack.add(1);
         stack.add(2);
         stack.add(3);
         stack.add(4);
         System.out.println(stack.get());
         System.out.println(stack.get());
         System.out.println(stack.get());
         System.out.println(stack.get());
         System.out.println(stack.get());
     }
}

ผลที่ได้