Java敏捷开发技巧之消除代码异味

来源：赛迪网作者：yongbing 出处：巧巧读书 2007-12-28 进入讨论组

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谢谢收藏 http://www.qqread.com/java/2007/12/w389616.html

条件下的代码还是不怎么一样，不如再抽象一点：

class CADApp {  
void drawShapes(Graphics graphics, Shape shapes[]) { 
for (int i = 0; i < shapes.length; i++) {
if (shapes[i] instanceof Line) { 
画出形状;   
} else if (shapes[i] instanceof Rectangle) { 
画出形状;   
} else if (shapes[i] instanceof Circle) {
画出形状;   
}
}
}
}

好，现在三个分支下的代码都一样了。我们也就不需要条件分支了：

class CADApp {  
void drawShapes(Graphics graphics, Shape shapes[]) {
for (int i = 0; i < shapes.length; i++) {
画出形状;
}
}
}

最后，将“画出形状”这个伪码写成代码吧！

class CADApp {
void drawShapes(Graphics graphics, Shape shapes[]) {
for (int i = 0; i < shapes.length; i++) {
shapes[i].draw(graphics);
}
}
}

当然，我们需要在每种Shape的类里面提供draw这个方法：

abstract class Shape {
abstract void draw(Graphics graphics);
}   
class Line extends Shape {
Point startPoint; 
Point endPoint; 
void draw(Graphics graphics) {
graphics.drawLine(getStartPoint(), getEndPoint());
}
}   
class Rectangle extends Shape {
Point lowerLeftCorner; 
Point upperRightCorner; 
void draw(Graphics graphics) {
graphics.drawLine(...);
graphics.drawLine(...);
graphics.drawLine(...);
graphics.drawLine(...);
}
}   
class Circle extends Shape {
Point center; 
int radius;
void draw(Graphics graphics) {
graphics.drawCircle(getCenter(), getRadius());
}
}

将抽象类变成接口

现在，看一下Shape这个类，它本身没有实际的方法。所以，它更应该是一个接口：

interface Shape {   
void draw(Graphics graphics);
}   
class Line implements Shape {   
...  
}   
class Rectangle implements Shape {  
...  
}   
class Circle implements Shape { 
...  
}

改进后的代码

改进后的代码就像下面这样：

interface Shape {   
void draw(Graphics graphics);
}   
class Line implements Shape {   
Point startPoint;
Point endPoint;  
void draw(Graphics graphics) {   
graphics.drawLine(getStartPoint(), getEndPoint());   
}
}   
class Rectangle implements Shape {  
Point lowerLeftCorner;   
Point upperRightCorner;  
void draw(Graphics graphics) {   
graphics.drawLine(...);  
graphics.drawLine(...);  
graphics.drawLine(...);  
graphics.drawLine(...);  
}
}   
class Circle implements Shape { 
Point center;
int radius;  
void draw(Graphics graphics) {   
graphics.drawCircle(getCenter(), getRadius());   
}
}   
class CADApp {  
void drawShapes(Graphics graphics, Shape shapes[]) { 
for (int i = 0; i < shapes.length; i++) {
shapes[i].draw(graphics);
}
}
}