public interface Command {

    void execute();

}

public class ConsolePrintCommand {

    public void execute() {
        System.out.println("This is a ConsolePrintCommand!");
    }

}

wes109 wrote:

画图软件的工具箱就是一个很好的例子:
用户选择不同的工具,就保存一个不同的Command对象
在画板上拖拽的时候,调用对象的execute方法
执行画圆或画方的操作

在《设计模式》中，client将command对象保存在invoker中，然后调用execute()

我觉得这只用一种应用而已，invoker和此模式没什么关系

public class ClientB
{
  public ClientB()
  {
  }
  
  public static void main(String args[])
  {
    DrawPane pane = new DrawPane();
    LineShape line = new LineShape();
    CircularShape circular = new CircularShape();
    QuadrateShape quadrate = new QuadrateShape();
  
    pane.drawObject(line);
    pane.drawObject(circular);
    pane.drawObject(quadrate);
      
  }

}

interface ShapeObject
{
  public String getShape();
  public void draw();
}

class DrawPane
{ 
    java.util.ArrayList shapeList = new java.util.ArrayList();
    
    public void drawObject(ShapeObject so)
    {
       shapeList.add(so);
       this.repaint(); 
       System.out.println("--------------------------");      
    }
    
    public void repaint()
    {      
      for(int i=0;i<shapeList.size();i++)
      {
        System.out.print(i+":");
        ((ShapeObject)shapeList.get(i)).draw();
      }
      
    }
    
}

 class LineShape implements ShapeObject 
 {
    public String getShape()
    {
       return "画线";
    }
    public void draw()
    {
       System.out.println(this.getShape());
    }
 }
 
 class CircularShape implements ShapeObject
 {
   public String getShape()
   {
     return "画圆";
   }
 
   public void draw()
   {
     System.out.println(this.getShape());
   }
 
 }
 
 class QuadrateShape implements ShapeObject
 {
   public String getShape()
   {
     return "画方";
   }
 
   public void draw()
   {
     System.out.println(this.getShape());
   }

WeiterWay wrote:
I think your DrawPane is the Invoker here. It is a command manager or command aggregator. Your implementation has one drawback: It is not a good idea to let command object implements shap object(the receiver or response object). this way the response object's interface is exposed to client (tight-coupled). it is better to embed the implementation details for command object, or even further maybe we can use bridge pattern to externalize the command receiver's implementation.