場景

這個場景好像不用太多說淋淀，主要是減少new的數(shù)量，確保實例唯一覆醇。

代碼

//version1
public class SingleFactory {
    private static SingleFactory singleFactory = new SingleFactory();
    private SingleFactory(){
        System.out.println("init method");
    }
    public static SingleFactory getInstance(){
        return singleFactory;
    }
}

public class HungrySingleFactory {
    private static HungrySingleFactory hungrySingleFactory;
    private HungrySingleFactory(){
        System.out.println("init");
    }
    public static HungrySingleFactory getInstance(){
        if(hungrySingleFactory == null) {
            synchronized (HungrySingleFactory.class) {
                if(hungrySingleFactory == null) {
                    hungrySingleFactory = new HungrySingleFactory();
                }
            }
        }
        return hungrySingleFactory;
    }
}

定義

保證一個類只有一個實例朵纷，并提供一個訪問它的全局訪問點

類圖

單例模式.gif

場景

現(xiàn)在公交車都是上車刷卡。但是在90年代初都是在每輛公交車上有收費員跟隨公交車永脓，每站上車來的人需要和收費員買票

代碼

public class Ticket {
    private String startStation;
    private String endStation;
    private int stationNum;
    private double money;
}

public class Passenger {
    private Ticket ticket;
    public Ticket getTicket() {
        return ticket;
    }
    public void setTicket(Ticket ticket) {
        this.ticket = ticket;
    }
}

public class Bus {
    private List<Passenger> passengerList = new ArrayList<Passenger>();
    public void addPassenger(Passenger passenger) {
        passengerList.add(passenger);
    }
    public void removePassenger(Passenger passenger) {
        passengerList.remove(passenger);
    }
    public int getPassengerNum() {
        return passengerList.size();
    }
    public Passenger getPassenger(int index) {
        return passengerList.get(index);
    }
}

public interface Iterator {
    public boolean hasNext();
    public Object next();
}

public class Cashier implements Iterator {
    private Bus bus;
    public Cashier(Bus bus) {
        this.bus = bus;
    }
    int num = 1;
    public void reset(){
        num = 1;
    }
    public boolean hasNext() {
        return num < bus.getPassengerNum();
    }
    public Passenger next() {
        Passenger passenger = bus.getPassenger(num);
        num++;
        return passenger;
    }
    public void iterator() {
        reset();
        while(hasNext()){
            Passenger passenger = next();
            Ticket pTicket = passenger.getTicket();
            if(pTicket == null) {
                System.out.println("請你立刻買票");
            }
        }
    }
    public Ticket pushTicket(String startStation, String endStation, int stationNum, int money) {
        Ticket ticket = new Ticket();
        ticket.setStartStation(startStation);
        ticket.setEndStation(endStation);
        ticket.setStationNum(stationNum);
        ticket.setMoney(money);
        return ticket;
    }
}

public class Tester {
    public static void main(String[] args) {
        Bus bus = new Bus();
        Cashier cashier = new Cashier(bus);
        Passenger p1 = new Passenger();
        bus.addPassenger(p1);
        Passenger p2 = new Passenger();
        Ticket ticket = cashier.pushTicket("上海","婺源",3, 10);
        p2.setTicket(ticket);
        bus.addPassenger(p2);
        Passenger p3 = new Passenger();
        bus.addPassenger(p3);
        cashier.iterator();
      
        Passenger p4 = new Passenger();
        bus.addPassenger(p4);
        bus.removePassenger(p2);
        cashier.iterator();
    }
}

定義

提供一種方法順序訪問一個聚合對象中各個元素袍辞，而又不暴露該對象的內(nèi)部表示。

類圖

Iterator.gif