行为型 - 状态(State)

状态模式(State pattern): 允许对象在内部状态改变时改变它的行为, 对象看起来好象改了它的类。@pdai

• 行为型 - 状态(State)

• 意图

• 类图

• 实现

意图

允许对象在内部状态改变时改变它的行为，对象看起来好像修改了它所属的类。

类图

c5085437-54df-4304-b62d-44b961711ba7.png

实现

糖果销售机有多种状态，每种状态下销售机有不同的行为，状态可以发生转移，使得销售机的行为也发生改变。

396be981-3f2c-4fd9-8101-dbf9c841504b.jpg

    public interface State {
        /** * 投入 25 分钱 */
        void insertQuarter();

        /** * 退回 25 分钱 */
        void ejectQuarter();

        /** * 转动曲柄 */
        void turnCrank();

        /** * 发放糖果 */
        void dispense();
    }

    public class HasQuarterState implements State {

        private GumballMachine gumballMachine;

        public HasQuarterState(GumballMachine gumballMachine) {
            this.gumballMachine = gumballMachine;
        }

        @Override
        public void insertQuarter() {
            System.out.println("You can't insert another quarter");
        }

        @Override
        public void ejectQuarter() {
            System.out.println("Quarter returned");
            gumballMachine.setState(gumballMachine.getNoQuarterState());
        }

        @Override
        public void turnCrank() {
            System.out.println("You turned...");
            gumballMachine.setState(gumballMachine.getSoldState());
        }

        @Override
        public void dispense() {
            System.out.println("No gumball dispensed");
        }
    }

    public class NoQuarterState implements State {

        GumballMachine gumballMachine;

        public NoQuarterState(GumballMachine gumballMachine) {
            this.gumballMachine = gumballMachine;
        }

        @Override
        public void insertQuarter() {
            System.out.println("You insert a quarter");
            gumballMachine.setState(gumballMachine.getHasQuarterState());
        }

        @Override
        public void ejectQuarter() {
            System.out.println("You haven't insert a quarter");
        }

        @Override
        public void turnCrank() {
            System.out.println("You turned, but there's no quarter");
        }

        @Override
        public void dispense() {
            System.out.println("You need to pay first");
        }
    }

    public class SoldOutState implements State {

        GumballMachine gumballMachine;

        public SoldOutState(GumballMachine gumballMachine) {
            this.gumballMachine = gumballMachine;
        }

        @Override
        public void insertQuarter() {
            System.out.println("You can't insert a quarter, the machine is sold out");
        }

        @Override
        public void ejectQuarter() {
            System.out.println("You can't eject, you haven't inserted a quarter yet");
        }

        @Override
        public void turnCrank() {
            System.out.println("You turned, but there are no gumballs");
        }

        @Override
        public void dispense() {
            System.out.println("No gumball dispensed");
        }
    }

    public class SoldState implements State {

        GumballMachine gumballMachine;

        public SoldState(GumballMachine gumballMachine) {
            this.gumballMachine = gumballMachine;
        }

        @Override
        public void insertQuarter() {
            System.out.println("Please wait, we're already giving you a gumball");
        }

        @Override
        public void ejectQuarter() {
            System.out.println("Sorry, you already turned the crank");
        }

        @Override
        public void turnCrank() {
            System.out.println("Turning twice doesn't get you another gumball!");
        }

        @Override
        public void dispense() {
            gumballMachine.releaseBall();
            if (gumballMachine.getCount() > 0) {
                gumballMachine.setState(gumballMachine.getNoQuarterState());
            } else {
                System.out.println("Oops, out of gumballs");
                gumballMachine.setState(gumballMachine.getSoldOutState());
            }
        }
    }

    public class GumballMachine {

        private State soldOutState;
        private State noQuarterState;
        private State hasQuarterState;
        private State soldState;

        private State state;
        private int count = 0;

        public GumballMachine(int numberGumballs) {
            count = numberGumballs;
            soldOutState = new SoldOutState(this);
            noQuarterState = new NoQuarterState(this);
            hasQuarterState = new HasQuarterState(this);
            soldState = new SoldState(this);

            if (numberGumballs > 0) {
                state = noQuarterState;
            } else {
                state = soldOutState;
            }
        }

        public void insertQuarter() {
            state.insertQuarter();
        }

        public void ejectQuarter() {
            state.ejectQuarter();
        }

        public void turnCrank() {
            state.turnCrank();
            state.dispense();
        }

        public void setState(State state) {
            this.state = state;
        }

        public void releaseBall() {
            System.out.println("A gumball comes rolling out the slot...");
            if (count != 0) {
                count -= 1;
            }
        }

        public State getSoldOutState() {
            return soldOutState;
        }

        public State getNoQuarterState() {
            return noQuarterState;
        }

        public State getHasQuarterState() {
            return hasQuarterState;
        }

        public State getSoldState() {
            return soldState;
        }

        public int getCount() {
            return count;
        }
    }

    public class Client {

        public static void main(String[] args) {
            GumballMachine gumballMachine = new GumballMachine(5);

            gumballMachine.insertQuarter();
            gumballMachine.turnCrank();

            gumballMachine.insertQuarter();
            gumballMachine.ejectQuarter();
            gumballMachine.turnCrank();

            gumballMachine.insertQuarter();
            gumballMachine.turnCrank();
            gumballMachine.insertQuarter();
            gumballMachine.turnCrank();
            gumballMachine.ejectQuarter();

            gumballMachine.insertQuarter();
            gumballMachine.insertQuarter();
            gumballMachine.turnCrank();
            gumballMachine.insertQuarter();
            gumballMachine.turnCrank();
            gumballMachine.insertQuarter();
            gumballMachine.turnCrank();
        }
    }

    You insert a quarter
    You turned...
    A gumball comes rolling out the slot...
    You insert a quarter
    Quarter returned
    You turned, but there's no quarter
    You need to pay first
    You insert a quarter
    You turned...
    A gumball comes rolling out the slot...
    You insert a quarter
    You turned...
    A gumball comes rolling out the slot...
    You haven't insert a quarter
    You insert a quarter
    You can't insert another quarter
    You turned...
    A gumball comes rolling out the slot...
    You insert a quarter
    You turned...
    A gumball comes rolling out the slot...
    Oops, out of gumballs
    You can't insert a quarter, the machine is sold out
    You turned, but there are no gumballs
    No gumball dispensed