设计模式之桥接模式

桥接模式用于把抽象化与实现化解耦，使两者可以独立变化。把这种多角度分类分离出来，让它们独立变化，减少它们之间的耦合。

桥接模式的优点是抽象和实现分离，扩展性好，实现细节对客户透明；缺点是会增加系统的理解与设计难度，聚合关系建立在抽象层，要求开发者对抽象进行设计与编程。

1. 创建桥接的接口；

public interface DrawAPI {
    void drawCircle(int radius, int x, int y);
}
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2. 创建实现了桥接接口的实现类；

public class RedCircle implements DrawAPI {
    @Override
    public void drawCircle(int radius, int x, int y) {
        System.out.println("Drawing Circle[color:red, radius:"
                + radius + ",x:" + x + ",y:" + y + "]");
    }
}

public class GreenCircle implements DrawAPI {
    @Override
    public void drawCircle(int radius, int x, int y) {
        System.out.println("Drawing Circle[color:green, radius:"
                + radius + ",x:" + x + ",y:" + y + "]");
    }
}
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3. 使用桥接接口创建图形抽象类；

public abstract class Shape{
    DrawAPI drawAPI;

    protected Shape(DrawAPI drawAPI) {
        this.drawAPI = drawAPI;
    }

    abstract void draw();
}
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4. 创建图形抽象类的实现；

public class Circle extends Shape {

    private int x, y, radius;

    protected Circle(int x, int y, int radius, DrawAPI drawAPI) {
        super(drawAPI);
        this.x = x;
        this.y = y;
        this.radius = radius;
    }

    @Override
    void draw() {
        drawAPI.drawCircle(radius, x, y);
    }
}
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5. 创建启动类，测试结果。

public class BridgeInstance {
    public static void main(String[] args) {
        Shape redCircle = new Circle(100, 100, 10, new RedCircle());
        redCircle.draw();
        Shape greenCircle = new Circle(50, 50, 5, new GreenCircle());
        greenCircle.draw();
    }
}
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