Java Integer Stack

/**
 * Program Stack (tumpukan) dengan Java
 * Author: Riyanto
 * Website: kangriyanto.wordpress.com | melonkoding.com 
 */

class Stack {
    
    private int[] items;
    private int size;
    private int top;
    
    public Stack(int size) {
        this.size = size;
        items = new int[size];
        top = -1;
    }
    
    public boolean isEmpty() {
        return top == -1;
    }
    
    public boolean isFull() {
        return top + 1 == size;
    }
    
    public int peek() {
        if (top == -1) {
            System.out.println("Stack kosong");
            return -1;
        }
        return items[top];
    }
    
    public int pop() {
        if (top == -1) {
            System.out.println("Stack kosong");
            return -1;
        }
        int item = items[top];
        top--;
        return item;
    }
    
    public void push(int item) {
        if(top == size - 1) {
            System.out.println("Stack penuh");
        } else {
            top++;
            items[top] = item;
        }
    }
    
    public int size() {
        return top + 1;
    }
    
    public static void main(String[] args) {
        Stack s = new Stack(3);
        
        // tambah item
        s.push(1);
        s.push(2);
        s.push(3);
        
        // apakah penuh
        System.out.println("Penuh? : "+ s.isFull());
        
        // lihat item teratas
        System.out.println("Teratas: "+ s.peek());
        
        // apakah kosonh
        System.out.println("Kosong?: "+ s.isEmpty());
        
        // ambil item teratas
        System.out.println("Ambil  : "+ s.pop());
        System.out.println("Ambil  : "+ s.pop());
        
        // apakah kosong
        System.out.println("Kosong?: "+ s.isEmpty());
        
        // berapa jumlah item
        System.out.println("Ukuran : "+ s.size());
    }
}