Effective Java 之-----消除过期的对象引用

public class Stack {
    private Object[] elements;
    private int size = 0;
    private static final int DEFAULT_CAPACITY = 16;

    public Stack() {
        elements = new Object[DEFAULT_CAPACITY];
    }

    public void push(Object e){
        ensureCapacity();
        elements[size++] = e;
    }

    public Object pop(){
        if(size == 0){
            throw new EmptyStackException();
        }
        return elements[--size];
    }

    private void ensureCapacity() {
        if(elements.length == size){
            elements = Arrays.copyOf(elements,2*size+1);
        }
    }
}                            public class Stack {
    private Object[] e