桥接模式

意图

将抽象与实现分离，使两者可独立变化。避免「多维度组合」导致类爆炸（如 RedCircle、BlueCircle、RedSquare…）。

类图

Java 示例

public interface DrawAPI {
    void drawCircle(int x, int y, int radius);
}

public class DrawRed implements DrawAPI {
    public void drawCircle(int x, int y, int r) {
        System.out.println("red circle @" + x + "," + y + " r=" + r);
    }
}

public class DrawBlue implements DrawAPI {
    public void drawCircle(int x, int y, int r) {
        System.out.println("blue circle @" + x + "," + y + " r=" + r);
    }
}

public abstract class Shape {
    protected final DrawAPI drawAPI;
    protected Shape(DrawAPI api) { this.drawAPI = api; }
    public abstract void draw();
}

public class Circle extends Shape {
    private int x, y, radius;
    public Circle(int x, int y, int r, DrawAPI api) {
        super(api);
        this.x = x; this.y = y; this.radius = r;
    }
    public void draw() { drawAPI.drawCircle(x, y, radius); }
}

新增颜色只加 DrawAPI 实现，新增形状只加 Shape 子类。

下一节：组合模式