构建可扩展的Java图表组件_Java_站长学院

构建可扩展的Java图表组件

[2005-12-26 00:00:00] 作者：Northz.com 来源：北方站长站

→Tags:组件图表扩展构建 int public 一个坐标我们数据 ←

图2-4
　　由这个类图，我们可以很容易的写出它的代码：

public interface ChartWidget{
　public int getX();
　public int getY();
　public int getWidth();
　public int getHeight();
　public void draw(Graphics g);
}

　　坐标轴(Axis)
　　接下来的一个类是坐标轴Axis。坐标轴主要任务是绘制轴及其刻度(Tick)和刻度值，因为它绘制时是按一定的比例绘制的，所以它需要有一个比例尺将实际坐标值转换值成屏幕坐标值。这就引出了Scale这个类。Scale类主要完成实际坐标值到屏幕坐标值以及屏幕坐标值到实际坐标值的相互转化。由此，Axis与Scale是一对相互依赖的类。从设计模式的角度来看，Axis是视图(View)，负责界面绘制，Scale就是它的模型(Model)，负责提供相应的数据。它们的类图见图2-5：
构建可扩展的Java图表组件

图2-5
　　下面来分别看看Axis类与Scale类的代码：

public abstract class Axis implements ChartWidget
{
protected Scale scale;
protected int x;
protected int y;
protected int width;
protected int height;
protected Axis peerAxis;
protected boolean drawGrid;
protected Color gridColor;
protected Color axisColor;
protected int tickLength;
protected int tickCount;
public Axis()
{
gridColor = Color.LIGHT_GRAY;
axisColor = Color.BLACK;
tickLength = 5;
drawGrid = false;
}
public int getTickCount(){ return tickCount;}
public void setTickCount(int tickCount){this.tickCount=tickCount;}
public Scale getScale(){ return scale;}
public void setScale(Scale scale){ this.scale = scale;}
public int getX(){ return x;}
public void setX(int x){this.x = x;}
public int getY(){ return y;}
public void setY(int y){this.y = y;}
public int getHeight(){ return height;}
public void setHeight(int height){this.height = height;}
public int getWidth(){ return width;}
public void setWidth(int width){this.width = width;}
public boolean isDrawGrid(){return drawGrid;}
public void setDrawGrid(boolean drawGrid){this.drawGrid=drawGrid;}
public Color getAxisColor(){return axisColor;}
public void setAxisColor(Color axisColor){ this.axisColor=axisColor;}
public Color getGridColor(){return gridColor;}
public void setGridColor(Color gridColor){this.gridColor=gridColor;}
public int getTickLength(){return tickLength;}
public void setTickLength(int tickLength){this.tickLength=tickLength;}
public Axis getPeerAxis(){return peerAxis;}
public void setPeerAxis(Axis peerAxis){this.peerAxis = peerAxis;}protected abstract int calculateTickLabelSize(Graphics g);}
public abstract class Scale{
protected double min;
protected double max;
protected int screenMin;
protected int screenMax;
public abstract int getScreenCoordinate(double value);
public double getActualValue(int value)
{
double vrange = max - min;
if(min < 0.0 && max < 0.0)
vrange = (min - max) * -1.0;
double i = screenMax - screenMin;
i = ((double)(value - screenMin) * vrange) / i;
i += min;
return i;
}
public void setMax(double max){this.max = max;}
public void setMin(double min){this.min = min;}
public double getMax(){return max;}
public double getMin(){return min;}
public int getScreenMax(){return screenMax;}
public int getScreenMin(){return screenMin;}
public void setScreenMax(int screenMax){this.screenMax =screenMax;}
public void setScreenMin(int screenMin){this.screenMin = screenMin;}
}

　　在上面的Axis类代码中，我们在原有的ChartWidget接口的基础上，为Axis添加了几个其它的属性：轴线的颜色axisColor，网格线的颜色gridColor及网格线的可见属性drawGrid。还有刻度线的长度和个数tickLength和tickCount。而peerAxis属性是参考坐标轴，在绘制坐标轴时的会用到。 Scale类也是抽象的，因为横轴和纵轴的屏幕坐标的转换方式不一样，所以getScreenCoordinate()方法留待子类来实现它。

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