java实现一个栈

java实现一个栈:

public class Stack<T> {    private ArrayList<T> mStack = new ArrayList<T>();    public void push(T value) {        synchronized (mStack) {            mStack.add(value);        }    }    public T pop() {        synchronized (mStack) {            int size = mStack.size();            return mStack.get(size -1);        }    }}