import java.util.Arrays;
/**
* Created by Great on 2017/2/23.
*/
public class Stack {
private final int DEFAULT_SIZE = 20;
private int base;
private int top;
private int[] array = new int[DEFAULT_SIZE];
public void push(Integer e) {
if (top == array.length){
array = Arrays.copyOf(array, array.length + DEFAULT_SIZE);
}
array[top] = e;
++top;
}
public Integer pop(){
if (top == 0) return null;
top--;
return array[top];
}
public int size() {
return top;
}
public boolean isEmpty(){
return top == 0;
}
}