呼叫具有圖形克作爲其參數的方法

Question

Shape類已經當我寫一個抽象的拉伸，這需要Graphics對象...例如，如果我想繪製一個矩形，在殼體2：

shapetype.draw(g); // he said that g is undefined 

應該怎麼爲了調用函數拉伸（克）初始化克：

public class main extends Applet 
    { 
     Shape shapetype; // shapeClass has 3 subclasses 

     public void init() 
     { 
      super.init(); 

// ask user to choose the type of shape 1-line 2-rectangle 3-oval 
// int choice = the type of shape   
      switch(choice) 
      { 

       case 1: 
       // draw line 
        break; 

       // draw Rectangle 
       case 2: 
       //ask user for x,y,width and height 
       shapetype = new Rectangle(x1,y1,w,h); 
       shapetype.draw(g); // to draw a rectangle 
        break; 

       case 3: 
       // draw Oval 
        break; 

       default: 
        break; 
      } 
     } 

     public void paint(Graphics g) 
     {super.paint(g); } 

    } 

Answer 1

移動繪圖調用到paint方法：

@Overrride // since you're overriding. 
public void paint(Graphics g) { 
    super.paint(g); 

    if(shapetype != null) { 
     shapetype.draw(g); 
    } 
} 

只繪製一次形狀是不夠的，每調用一次paint就會被覆蓋，所以需要重繪。