设计模式的分类

根据Design Patterns - Elements of Reusable Object-Oriented Software（中文译名：设计模式 - 可复用的面向对象软件元素）一书，总体来说设计模式分为三大类：

创建型模式，共五种：工厂方法模式、抽象工厂模式、单例模式、建造者模式、原型模式。

结构型模式，共七种：适配器模式、装饰器模式、代理模式、外观模式、桥接模式、组合模式、享元模式。

行为型模式，共十一种：策略模式、模板方法模式、观察者模式、迭代子模式、责任链模式、命令模式、备忘录模式、状态模式、访问者模式、中介者模式、解释器模式。

单例模式

// 懒汉式
public class Singleton {
    private static Singleton instance;
    private Singleton() {
        
    }
    public static Singleton getInstance() {
        if (instance == null) {
            instance = new Singleton();
            return instance;
        }
    }
}

//饿汉式
public class Singleton {
    private static Singleton instance = new Singleton();
    private Singleton() {
        
    }
    public static Singleton getInstance() {
        return instance;
    }
}

// 双重检查
public class Singleton {
    private static Singleton instance;
    private Singleton() {
        
    }
    public static Singleton getInstance() {
        if (instance == null) {
            synchronized (Singleton.class) {
                if (instance == null) {
                    instance = new Singleton();
                    return instance;
                }
            }
        }
    }
}

工厂模式（Factory Pattern）

public class ShapeFactory {
    public Shape getShape(String shapeType) {
        if (shapeType == null) {
            return null;
        }
        if (shapeType.equalsIgnoreCase("CIRCLE")) {
            return new Circle();
        }
        if (shapeType.equalsIgnoreCase("RECTANGLE")) {
            return new Rectangle();
        }
        if (shapeType.equalsIgnoreCase("SQUARE")) {
            return new Square();
        }
        return null;
    }
    
}

生成器模式

// 生成器模式
public class ShapeMaker {
    private Shape circle;
    private Shape rectangle;
    private Shape square;
    public void draw() {
        circle.draw();
        rectangle.draw();
        square.draw();
    }
    public void setCircle(Shape circle) {
        this.circle = circle;
    }
    public void setRectangle(Shape rectangle) {
        this.rectangle = rectangle;
    }
    public void setSquare(Shape square) {
        this.square = square;
    }
}

原型模式

//原型模式
public class ShapeCache {
    private static Map<String, Shape> shapeMap = new HashMap<>();
    public static Shape getShape(String shapeId) {
        Shape cachedShape = shapeMap.get(shapeId);
        return cachedShape.clone();
    }
    public static void loadCache() {
        Circle circle = new Circle();
        circle.setId("1");
        shapeMap.put(circle.getId(), circle);
        Rectangle rectangle = new Rectangle();
        rectangle.setId("2");
        shapeMap.put(rectangle.getId(), rectangle);
        Square square = new Square();
        square.setId("3");
        shapeMap.put(square.getId(), square);
    }
}

适配器模式

public class ShapeDecorator implements Shape {
    protected Shape decoratedShape;
    public ShapeDecorator(Shape decoratedShape) {
        this.decoratedShape = decoratedShape;
    }
    public void draw() {
        decoratedShape.draw();
    }
}
public class RedShapeDecorator extends ShapeDecorator {
    public RedShapeDecorator(Shape decoratedShape) {
        super(decoratedShape);
        decoratedShape.setBorderColor("Red");
    }
    public void setBorderColor(String borderColor) {
        decoratedShape.setBorderColor(borderColor);
    }
}

装饰者模式

代理模式

外观模式

参考

23中设计模式菜鸟教程-设计模式