接口型模式

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设计模式

1.Adapter(适配器)模式

对象适配器(Object Adapter)

public interface IPeg {
	void insertIntoHole();
}
public class SquarePeg implements IPeg {
	@Override
	public void insertIntoHole() {
		System.out.println("I'm inserting into square hole...");
		// other logic...
	}
}
public interface IRoundPeg {
	void insertIntoRoundHole();
}
public class RoundPeg implements IRoundPeg {
	@Override
	public void insertIntoRoundHole() {
		System.out.println("I'm inserting into round hole...");
		// other logic...
	}
}
public class RoundPegAdapter implements IPeg {
	private IRoundPeg roundPeg;

	public RoundPegAdapter(IRoundPeg roundPeg) {
		this.roundPeg = roundPeg;
	}

	@Override
	public void insertIntoHole() {
		roundPeg.insertIntoRoundHole();
	}
}

类适配器

public class RoundPegAdapter2 extends RoundPeg implements IPeg {
	@Override
	public void insertIntoHole() {
		super.insertIntoRoundHole();
	}
}

双向适配器

public class TwoWayPegAdapter implements IRoundPeg, IPeg {
	private IPeg squarePeg;
	private IRoundPeg roundPeg;

	public TwoWayPegAdapter(IPeg squarePeg) {
		this.squarePeg = squarePeg;
	}

	public TwoWayPegAdapter(IRoundPeg roundPeg) {
		this.roundPeg = roundPeg;
	}

	@Override
	public void insertIntoRoundHole() {
		squarePeg.insertIntoHole();
	}

	@Override
	public void insertIntoHole() {
		roundPeg.insertIntoRoundHole();
	}
}

测试

public class TestDrive {
	public static void main(String[] args) {
		TestDrive test = new TestDrive();
		IPeg squarePeg = new SquarePeg();
		IRoundPeg roundPeg = new RoundPeg();
		RoundPegAdapter adpater = new RoundPegAdapter(roundPeg);
		System.out.println("Testing square peg...");
		test.testPeg(squarePeg);
		System.out.println("\nTesting square adapter peg...");
		test.testPeg(adpater);
		TwoWayPegAdapter roundPeg2 = new TwoWayPegAdapter(roundPeg);
		TwoWayPegAdapter squarePeg2 = new TwoWayPegAdapter(squarePeg);
		System.out.println("\nTesting a 2-way square adapter peg...");
		test.testPeg(roundPeg2);
		System.out.println("\nTesting 2-way round adapter peg...");
		test.testRoundPeg(squarePeg2);
	}

	private void testPeg(IPeg peg) {
		peg.insertIntoHole();
	}

	private void testRoundPeg(IRoundPeg peg) {
		peg.insertIntoRoundHole();
	}
}

2.Facade(外观)模式

目的：提供一个接口，使子系统更加容易使用。

通常，我们应该把子系统中的类重构为一个个目的明确的类。这样做可以使代码更加容易维护，但是这样也会让子系统用户不知从何处开始。为了便于子系统用户的使用，我们可以在子系统中顺带提供一些示例类或者外观类。示例类通常是指能够独立运行但不可复用的应用程序，仅用来示范子系统的用法。外观类通常是一个可配置、可复用的类，它为方便用户使用子系统提供了一个更高层次的接口。

总结：外观封装了子系统之间复杂的交互和依赖关系,为客户对象提供了单一简单的界面,降低了系统的复杂性。在讲解外观模式同时,介绍了最少知识原则,我们知道,类之间耦合度越低,越易扩展和实现重用。

public class HotelReceptionist {
    public void subscribe() {
        System.out.println("Subscribe a table...");
    }
}
public class Cook {
    public void cookDish() {
        System.out.println("Cooking dishes...");
    }
}
public class Waitress {
    public void serveDishes() {
        System.out.println("Serving dishes...");
    }

    public void waitForAnOrder() {
        System.out.println("Waiting for the order...");
    }
}
public class Cashier {
    public void check() {
        System.out.println("Check the bill...");
    }
}
public class Assistant {
    private HotelReceptionist hotelReceptionist;
    private Cook cook;
    private Waitress waitress;
    private Cashier cashier;

    public Assistant(HotelReceptionist hotelReceptionist, Cook cook, Waitress waitress, Cashier cashier) {
        this.hotelReceptionist = hotelReceptionist;
        this.cook = cook;
        this.waitress = waitress;
        this.cashier = cashier;
    }

    public void prepareDinner() {
        hotelReceptionist.subscribe();
        waitress.waitForAnOrder();
        cook.cookDish();
    }

    public void endDinner() {
        waitress.serveDishes();
        cashier.check();
    }
}
public class Boss {
    private Assistant assistant;

    public Boss(Assistant assistant) {
        this.assistant = assistant;
    }

    public void treat() {
        assistant.prepareDinner();
        address();
        assistant.endDinner();
    }

    private void address() {
        System.out.println("Boss is bitching : \"Tomorrow is going to be better, we will make blah blah...\"");
    }
}
public class FacadeTestDrive {
    public static void main(String[] args) {
       Cashier cashier = new Cashier();
       Cook cook = new Cook();
       HotelReceptionist hotelReceptionist = new HotelReceptionist();
       Waitress waitress = new Waitress();
       Assistant assistant = new Assistant(hotelReceptionist, cook, waitress, cashier);

       Boss boss = new Boss(assistant);

       boss.treat();
   }
}

3.Composite(组合)模式

目的：让用户能够用统一的接口处理单个对象以及对象组合。

常见的组合

Composite模式包含两个相关的重要概念。其中一个概念是群组可以包含个体对象，也可以包含其他的群组。与此相关的另一个概念是群组和个体对象可以共享同一个接口。将这些概念应用于对象建模，就可以创建一个抽象类或Java接口来定义群组对象和个体对象的公有特性。

组合对象模式中的方法通常采用递归定义。由于递归的存在，在编写代码的时候需要谨防死循环。不过，只要通过采取措施保证组合对象模型为树状结构，就可一避免这类问题。另外，组合对象模型中也可以出现环，但是我们必须修改算法来监控可能出现的无穷尽递归。

安全的组合模式

public abstract class BranchComponent {
    public String getName() {
        throw new UnsupportedOperationException();
    }

    public String getDiscription() {
        throw new UnsupportedOperationException();
    }

    public void display() {
        throw new UnsupportedOperationException();
    }
}
import java.util.ArrayList;
import java.util.List;
public class BranchComposite extends BranchComponent {
    private String name;
    private String discription;
    private List<BranchComponent> childrenBranch;

    public BranchComposite(String name, String discription) {
        this.name = name;
        this.discription = discription;
        childrenBranch = new ArrayList<BranchComponent>();
    }

    public void display() {
        System.out.printf("%s: %s\n", name, discription);
        for (BranchComponent child : childrenBranch) {
            child.display();
        }
    }

    public String getName() {
        return name;
    }

    public String getDiscription() {
        return discription;
    }

    public void add(BranchComponent child) {
        childrenBranch.add(child);
    }

    public void remove(BranchComponent child) {
        childrenBranch.remove(child);
    }

    public BranchComponent getChild(int index) {
        return childrenBranch.get(index);
    }
}
public class BranchLeaf extends BranchComponent {
    private String name;
    private String discription;

    public BranchLeaf(String name, String discription) {
        this.name = name;
        this.discription = discription;
    }

    public void display() {
        System.out.printf("\t%s: %s\n", name, discription);
    }

    public String getName() {
        return name;
    }

    public String getDiscription() {
        return discription;
    }
}
public class TestDrive {
    public static void main(String[] args) {
        BranchComposite china = new BranchComposite("CN", "China Branch");

        BranchComposite shanghai = new BranchComposite("Sh", "Shanghai Branch");
        BranchLeaf huangpu = new BranchLeaf("Hp", "Huangpu Branch");
        BranchLeaf yangpu = new BranchLeaf("Yp", "Yangpu Branch");
        BranchLeaf pudong = new BranchLeaf("Pd", "Pudong Branch");

        BranchComposite beijing = new BranchComposite("Bj", "Beijing Branch");
        BranchLeaf dongcheng = new BranchLeaf("Dc", "Dongcheng Branch");
        BranchLeaf xicheng = new BranchLeaf("Xc", "Xicheng Branch");
        BranchLeaf haidian = new BranchLeaf("Hd", "Haidian Branch");

        shanghai.add(huangpu);
        shanghai.add(yangpu);
        shanghai.add(pudong);

        beijing.add(dongcheng);
        beijing.add(xicheng);
        beijing.add(haidian);

        china.add(shanghai);
        china.add(beijing);

        System.out.println("Displaying the head bank information");
        display(china);

        System.out.println("\nDisplaying Shanghai bank branch information");
        display(shanghai);

        System.out.println("\nDisplaying Pudong bank branch information in Shanghai");
        display(pudong);
    }

    private static void display(BranchComponent branch) {
        branch.display();
    }
}

透明的组合模式

public abstract class BranchComponent {
    public String getName() {
        throw new UnsupportedOperationException();
    }

    public String getDiscription() {
        throw new UnsupportedOperationException();
    }

    public void display() {
        throw new UnsupportedOperationException();
    }

    public void add(BranchComponent child) {
        throw new UnsupportedOperationException();
    }

    public void remove(BranchComponent child) {
        throw new UnsupportedOperationException();
    }

    public BranchComponent getChild(int index) {
        throw new UnsupportedOperationException();
    }
}
import java.util.ArrayList;
import java.util.List;
public class BranchComposite extends BranchComponent {
    private String name;
    private String discription;
    private List<BranchComponent> childrenBranch;

    public BranchComposite(String name, String discription) {
        this.name = name;
        this.discription = discription;
        childrenBranch = new ArrayList<BranchComponent>();
    }

    public void display() {
        System.out.printf("%s: %s\n", name, discription);
        for (BranchComponent child : childrenBranch) {
            child.display();
        }
    }

    public String getName() {
        return name;
    }

    public String getDiscription() {
        return discription;
    }

    public void add(BranchComponent child) {
        childrenBranch.add(child);
    }

    public void remove(BranchComponent child) {
        childrenBranch.remove(child);
    }

    public BranchComponent getChild(int index) {
        return childrenBranch.get(index);
    }
}
public class BranchLeaf extends BranchComponent {
    private String name;
    private String discription;

    public BranchLeaf(String name, String discription) {
        this.name = name;
        this.discription = discription;
    }

    public void display() {
        System.out.printf("\t%s: %s\n", name, discription);
    }

    public String getName() {
        return name;
    }

    public String getDiscription() {
        return discription;
    }
}
public class TestDrive {
    public static void main(String[] args) {
        BranchComposite china = new BranchComposite("CN", "China Branch");

        BranchComposite shanghai = new BranchComposite("Sh", "Shanghai Branch");
        BranchLeaf huangpu = new BranchLeaf("Hp", "Huangpu Branch");
        BranchLeaf yangpu = new BranchLeaf("Yp", "Yangpu Branch");
        BranchLeaf pudong = new BranchLeaf("Pd", "Pudong Branch");

        BranchComposite beijing = new BranchComposite("Bj", "Beijing Branch");
        BranchLeaf dongcheng = new BranchLeaf("Dc", "Dongcheng Branch");
        BranchLeaf xicheng = new BranchLeaf("Xc", "Xicheng Branch");
        BranchLeaf haidian = new BranchLeaf("Hd", "Haidian Branch");

        shanghai.add(huangpu);
        shanghai.add(yangpu);
        shanghai.add(pudong);

        beijing.add(dongcheng);
        beijing.add(xicheng);
        beijing.add(haidian);

        china.add(shanghai);
        china.add(beijing);

        System.out.println("Displaying the head bank information");
        display(china);

        System.out.println("\nDisplaying Shanghai bank branch information");
        display(shanghai);

        System.out.println("\nDisplaying Pudong bank branch information in Shanghai");
        display(pudong);
    }

    private static void display(BranchComponent branch) {
        branch.display();
    }
}

4.Bridge(桥接)模式

意图：将抽象与抽象方法的实现相分离，这样他们就可以独立变化。

抽象就是指依赖于一系列抽象方法的类。最简单的抽象实例是抽象的类层次结构，其中超类中的具体类依赖于其他抽象类。如果希望用另一种机器的排列方式来构造最初的类层次结构，就必须把那些抽象的方法移到另一种类层次结构中。在这种情况下，我们可以使用Bridge模式，将抽象与其抽象方法的实现相分离。
Bridge模式是常见的例子就是驱动程序，比如数据库驱动程序。数据库驱动程序提供了Bridge模式结构中固有的权衡的良好实例。一个驱动程序可能会请求某个实现程序不支持的方法。另一方面，驱动程序可能会忽略应用到某个特定数据库的有用方法。这将迫使我们重新编写针对实现而不是抽象的代码。我们是否应该更重视抽象而不是具体并非一直都很明朗，但是有意地做这些决定是非常重要的.