从一个州转移到另一个州

Question

我使用集中式模式编码自动售货机。问题是我发现我无法改变状态。在构造函数中，我将状态初始化为Ls [0]，但是当我转到方法public void coin（）来改变状态时，我发现状态没有改变。我的代码部分是：

 class Vending_machine {

    State st;
    private int price;
    private int k;
    private int k1;
    private int t;
    private int s;
    private State[] Ls;

    public Vending_machine() {
        Ls = new State[7];
        Ls[0] = new Idle();
        Ls[1] = new Coins_inserted();
        Ls[2] = new Sugar();
        Ls[3] = new No_small_cups();
        Ls[4] = new No_large_cups();
        Ls[5] = new Exit();
        Ls[6] = new Start();
        st = Ls[0];
        st.vm = this;

        k = 0;
        k1 = 0;
        t = 0;
        price = 0;
        s = 0;

    }

    public void setK(int k) {
        this.k = k;

    }

    public int getK() {
        return k;
    }

    public void setS(int s) {
        this.s = s;
    }

    public int getS() {
        return s;
    }......


          public void coin() {
        st.coin();
        if (st.getId() == 0) {
            if (t + 25 < price) {
                // t=t+25;
                st = Ls[0];
            }
            if (t + 25 >= price && price > 0) {
                // s=0;
                // t=0;
                st = Ls[1];
            }
        }......

 class State {

    public Vending_machine vm;
    int id = 0;
    public void coin() {}
        public void small_cup() {}
        public void large_cup() {}
        public void sugar() {}
        public void tea() {}
        public void insert_large_cups(int n) {}
        public void insert_small_cups(int n) {}
        public void set_price(int p) {}
    .......
}
   class Idle extends State {
    public void coin() {
        if (vm.getT() + 25 < vm.getPrice()) {
            vm.setT((vm.getT()) + 25);
            System.out.println(vm.getT());
        }
        else if ((vm.getT() + 25 >= vm.getPrice()) && (vm.getPrice() > 0)) {
            vm.setS(0);
            vm.setT(0);
        }
    }......