本文共 2142 字,大约阅读时间需要 7 分钟。
装饰器模式(Decorator Pattern)允许向一个现有的对象添加新的功能,同时又不改变其结构。这种类型的设计模式属于结构型模式,它是作为现有的类的一个包装。
这种模式创建了一个装饰类,用来包装原有的类,并在保持类方法签名完整性的前提下,提供了额外的功能。 我们通过下面的实例来演示装饰器模式的用法。其中,我们将把一个形状装饰上不同的颜色,同时又不改变形状类。我们将创建一个 Shape 接口和实现了 Shape 接口的实体类。然后我们创建一个实现了 Shape 接口的抽象装饰类 ShapeDecorator,并把 Shape 对象作为它的实例变量。
RedShapeDecorator 是实现了 ShapeDecorator 的实体类。DecoratorPatternDemo,我们的演示类使用 RedShapeDecorator 来装饰 Shape 对象。步骤 1创建一个接口。Shape.javapublic interface Shape { void draw();}步骤 2创建实现接口的实体类。Rectangle.javapublic class Rectangle implements Shape { @Override public void draw() { System.out.println("Shape: Rectangle"); }}Circle.javapublic class Circle implements Shape { @Override public void draw() { System.out.println("Shape: Circle"); }}步骤 3创建实现了 Shape 接口的抽象装饰类。ShapeDecorator.javapublic abstract class ShapeDecorator implements Shape { protected Shape decoratedShape; public ShapeDecorator(Shape decoratedShape){ this.decoratedShape = decoratedShape; } public void draw(){ decoratedShape.draw(); } }步骤 4创建扩展了 ShapeDecorator 类的实体装饰类。RedShapeDecorator.javapublic class RedShapeDecorator extends ShapeDecorator { public RedShapeDecorator(Shape decoratedShape) { super(decoratedShape); } @Override public void draw() { decoratedShape.draw(); setRedBorder(decoratedShape); } private void setRedBorder(Shape decoratedShape){ System.out.println("Border Color: Red"); }}步骤 5使用 RedShapeDecorator 来装饰 Shape 对象。DecoratorPatternDemo.javapublic class DecoratorPatternDemo { public static void main(String[] args) { Shape circle = new Circle(); Shape redCircle = new RedShapeDecorator(new Circle()); Shape redRectangle = new RedShapeDecorator(new Rectangle()); System.out.println("Circle with normal border"); circle.draw(); System.out.println("\nCircle of red border"); redCircle.draw(); System.out.println("\nRectangle of red border"); redRectangle.draw(); }}步骤 6验证输出。Circle with normal borderShape: CircleCircle of red borderShape: CircleBorder Color: RedRectangle of red borderShape: RectangleBorder Color: Red
转载地址:http://ewfnx.baihongyu.com/