21.1

public class Test_21_1<E> {
    private int size;
    private static final int CAPACITY = 3;
    private E array[];
    
    public Test_21_1(){
        this(CAPACITY);
    }
    
    public Test_21_1(int n){
        array = (E[]) new Object[n];
    }
    
    public int getSize(){
        return size;
    }
    
    public E peek(){
        // return the top value
        return array[size - 1];
    }
    
    public void push(E o){
        //add element
        if(size >= array.length) {
            Object[] temp = new Object[array.length * 2];
            System.arraycopy(array, 0, temp, 0, array.length);
            array = (E[]) temp;
        }
        array[size++] = o;
    }
    
    public E pop(){
        //return and remove the top element
        return array[--size];
    }
    
    public boolean isEmpty(){
        return size == 0;
    }
    
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        int j;
        Test_21_1<String> t = new Test_21_1<String>();

        t.push("red");
        t.push("blue");
        t.push("black");
        
        j = t.size;
//        for( int i = 0; i < j; i++)
//        System.out.println(t.pop());
//        System.out.println(t.peek());
    }

}