如何将 Swing 程序转换为 MVC 形式？ [关闭]

Question

我从下面给出的链接获得了制作条形图的源代码 -

Bar chart in java

我创建了一个模型类来存储项目及其对应的值。然后，我制作了一个面板类，它应该只接受模型并将其显示为条形图。然后我创建了一个框架类，将面板添加到它的内容窗格中。然后，我创建了一个应该运行所有这些的驱动程序类，就像链接中给出的代码一样。

问题是我只看到我的框架而没有看到条形图。我该如何解决？

我故意不包含我的代码，因为它太大了。但是，如果你觉得我应该把它放在这里，那么请告诉我。

package myArea;

public class SimpleBarChartModel{

private String[] items;
private double[] valuesOfItems;
private String title;

public SimpleBarChartModel(String[] itemList, double[] valueList, String title){

    String[] items = itemList;
    double[] valuesOfItems = valueList;

}

public String[] getItems(){
    return items;
}

public void setItems(String[] items){
    this.items = items;
}

public double[] getValuesOfItems(){
    return valuesOfItems;
}

public void setValuesOfItems(double[] valuesOfItems){
    this.valuesOfItems = valuesOfItems;
}

public String getTitle(){
    return title;
}

public void setTitle(String title){
    this.title = title;
}


}


package myArea;

import java.awt.*;
import javax.swing.*;

public class SimpleBarChartPanel extends JPanel{

SimpleBarChartModel bChartMdl; 

public SimpleBarChartPanel(SimpleBarChartModel bcMdl){

    bChartMdl = bcMdl; 

}

public void paintComponent(Graphics graphics) {

//Must always be the first line in paintComponent method
super.paintComponent(graphics);
double[] values = bChartMdl.getValuesOfItems();
String[] items = bChartMdl.getItems();
String title = bChartMdl.getTitle();     

if (values == null || values.length == 0)
return;

double minValue = 0;
double maxValue = 0;

for (int i = 0; i < values.length; i++) {
    if (minValue > values[i]){

        minValue = values[i];
    }

    if (maxValue < values[i]){

        maxValue = values[i];
    }

}

Dimension dim = getSize();
int clientWidth = dim.width;
int clientHeight = dim.height;
int barWidth = clientWidth / values.length;
Font titleFont = new Font("Book Antiqua", Font.BOLD, 15);
FontMetrics titleFontMetrics = graphics.getFontMetrics(titleFont);
Font labelFont = new Font("Book Antiqua", Font.PLAIN, 10);
FontMetrics labelFontMetrics = graphics.getFontMetrics(labelFont);
int titleWidth = titleFontMetrics.stringWidth(title);
int q = titleFontMetrics.getAscent();
int p = (clientWidth - titleWidth) / 2;
graphics.setFont(titleFont);
graphics.drawString(title, p, q);
int top = titleFontMetrics.getHeight();
int bottom = labelFontMetrics.getHeight();

if (maxValue == minValue){
    return;
}


double scale = (clientHeight - top - bottom) / (maxValue - minValue);
q = clientHeight - labelFontMetrics.getDescent();
graphics.setFont(labelFont);

for (int j = 0; j < values.length; j++) {
    int valueP = j * barWidth + 1;
    int valueQ = top;
    int height = (int) (values[j] * scale);

    if (values[j] >= 0){

        valueQ += (int) ((maxValue - values[j]) * scale);
}else{
        valueQ += (int) (maxValue * scale);
        height = -height;
}

        graphics.setColor(Color.blue);
        graphics.fillRect(valueP, valueQ, barWidth - 2, height);
        graphics.setColor(Color.black);
        graphics.drawRect(valueP, valueQ, barWidth - 2, height);
        int labelWidth = labelFontMetrics.stringWidth(items[j]);
        p = j * barWidth + (barWidth - labelWidth) / 2;
        graphics.drawString(items[j], p, q);

    }

}   


}


package myArea;

import javax.swing.*;

public class SimpleBarChartView extends JFrame{

SimpleBarChartPanel bChartPanel;

public SimpleBarChartView(SimpleBarChartPanel bcPanel, int width, int height){

    bChartPanel = bcPanel;
    this.setSize(width, height);
    this.getContentPane().add(bChartPanel);
    this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}

}   


package myArea;

public class SimpleBarChartDriver {

public static void main(String[]args){

    double[] value= new double[5];
    String[] languages = new String[5];

    value[0] = 1;
    languages[0] = "Visual Basic";

    value[1] = 2;
    languages[1] = "PHP";

    value[2] = 3;
    languages[2] = "C++";

    value[3] = 4;
    languages[3] = "C";

    value[4] = 5;
    languages[4] = "Java";

            SimpleBarChartModel sBModel = 
            new SimpleBarChartModel(languages,value,"comp languages");
    SimpleBarChartPanel sBPanel = new SimpleBarChartPanel(sBModel);
    SimpleBarChartView sbView = new SimpleBarChartView(sBPanel, 500, 500);
    sbView.setVisible(true);    
}

}

更新 - 这些是我在运行驱动程序类时遇到的错误

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at sun.font.FontDesignMetrics.stringWidth(Unknown Source)

Answer 1

您正在隐藏类中的变量：

class SimpleBarChartModel {
   private String[] items;
   private double[] valuesOfItems;
   private String title;

   public SimpleBarChartModel(String[] itemList, double[] valueList,
         String title) {
      String[] items = itemList; // **** here
      double[] valuesOfItems = valueList;  // **** here
   }

如上所示，您正在重新声明类字段，因此实际字段将保持为空值。解决方法不是重新声明字段而是使用类字段：

class SimpleBarChartModel {
   private String[] items;
   private double[] valuesOfItems;
   private String title;

   public SimpleBarChartModel(String[] itemList, double[] valueList,
         String title) {
      items = itemList; // **** here
      valuesOfItems = valueList;  // **** here

      // !! missing something else here !! ;-)
   }

接下来，当您收到 NullPointerException 时，请检查引发异常的行。其中一个变量尚未初始化，您必须更正代码以使其初始化。