将我的类数据传递给驱动程序类会产生异常吗？

Question

我有这个类，它给了我颜色对象的 RGB 值。

import java.awt.*;
import java.util.Collection;
import java.util.HashMap;

public class ColorChooserRGB {
    public static void main(String[] args) {
        // Create new HashMap
        HashMap<String, Object> colorObjectsHashMap = new HashMap<>();

        // Fill with colors
        colorObjectsHashMap.put("black", Color.BLACK);
        colorObjectsHashMap.put("lightGray", Color.LIGHT_GRAY);
        colorObjectsHashMap.put("blue", Color.BLUE);
        colorObjectsHashMap.put("magenta", Color.MAGENTA);
        colorObjectsHashMap.put("cyan", Color.CYAN);
        colorObjectsHashMap.put("orange", Color.ORANGE);
        colorObjectsHashMap.put("darkGray", Color.DARK_GRAY);
        colorObjectsHashMap.put("pink", Color.PINK);
        colorObjectsHashMap.put("gray", Color.GRAY);
        colorObjectsHashMap.put("red", Color.RED);
        colorObjectsHashMap.put("green", Color.GREEN);
        colorObjectsHashMap.put("white", Color.WHITE);
        colorObjectsHashMap.put("yellow", Color.YELLOW);

        // Get all values from the HashMap and display them.
        System.out.println("Values of colorObjectsHashMap: ");
        Collection<Object> objValues = colorObjectsHashMap.values();
        for (Object value : objValues) {
            System.out.println("\t" + value);
        }
    }    

    public Color getColor(String selected) {
        return Color.decode(selected);
    }

    public Collection<Object> getKeySet() {
        return null;
    }
}

输出：

Values of colorObjectsHashMap:      
java.awt.Color[r=192,g=192,b=192]   
java.awt.Color[r=255,g=0,b=255]     
java.awt.Color[r=255,g=175,b=175]   
java.awt.Color[r=0,g=255,b=0]       
java.awt.Color[r=0,g=0,b=0]     
java.awt.Color[r=255,g=255,b=0]     
java.awt.Color[r=0,g=255,b=255]     
java.awt.Color[r=255,g=200,b=0]     
java.awt.Color[r=255,g=0,b=0]   
java.awt.Color[r=128,g=128,b=128]   
java.awt.Color[r=0,g=0,b=255]   
java.awt.Color[r=255,g=255,b=255]   
java.awt.Color[r=64,g=64,b=64]

FLOW：我需要在 ColorTest 类中使用我的新类 RGB 数据来选择一种颜色并以该颜色绘制一个形状。当它在“chooser = new ColorChooser();”处调用我的类时，我如何将我的 Object 数据传递给这个 ColorTest 类？我将 main 更改为“public Object[] colorChooser(List list)”并添加了“return objValues.toArray();”，但事实并非如此。那我回什么？我已经尝试了我的 IDE 中的一些建议，但它总是会引发更多问题。感谢您的帮助！

import javax.swing.*;
import javax.swing.event.ListSelectionEvent;
import javax.swing.event.ListSelectionListener;
import java.awt.*;

public class ColorTest extends JFrame {
    private JList<String> colorList;
    private ColorChooser chooser;
    private JPanel drawPanel;

    public ColorTest() {
        super("List Test");

        setLayout(new GridLayout(2, 1));
        chooser = new ColorChooser();

        // create a list with items in colorNames array
        colorList = new JList<String>(chooser.getKeySet().toArray(new String[0]));
        colorList.setVisibleRowCount(5);
        colorList.setSelectedIndex(0);

        // do not allow multiple selections
        colorList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);

        JPanel choosePanel = new JPanel();

        // add a JScrollPane containing JList to content pane
        choosePanel.add(new JScrollPane(colorList));

        // set up event handler
        colorList.addListSelectionListener(
                new ListSelectionListener() { // anonymous inner class
                    // handle list selection events
                    public void valueChanged(ListSelectionEvent event) {
                        repaint();
                    }
                }
        ); // end call to addListSelectionListener

        drawPanel = new JPanel(); // create a drawing panel
        drawPanel.setBackground(Color.WHITE);

        // add the panels to the window
        add(drawPanel);
        add(choosePanel);

        setSize(300, 300);
        setVisible(true);
    }

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

        // obtain the selected value
        Object selected = colorList.getSelectedValue();

        // set the color
        g.setColor(chooser.getColor((String)selected));

        // draw the rectangle
        Rectangle bounds = drawPanel.getVisibleRect();
        g.fillRect(bounds.x + 10, bounds.y + 30, bounds.width - 15, bounds.height - 15);
    }

    public static void main(String[] args) {
        ColorTest application = new ColorTest();
        application.setDefaultCloseOperation(EXIT_ON_CLOSE);
    }
} // end class ColorTest

结果： 线程“主”java.lang.NullPointerException 中的异常

---

更新的颜色选择器： ColorChooser 第 38 行 = 返回 Color.decode(objValues); ColorTest 第 62 行 = g.setColor(chooser.getColor((String)selected)); 结果：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at java.lang.Integer.decode(Integer.java:1161)
    at java.awt.Color.decode(Color.java:729)
    at edu.austincc.colors.ColorChooser.getColor(ColorChooser.java:38)
    at edu.austincc.colors.ColorTest.paint(ColorTest.java:62)
    at javax.swing.RepaintManager$4.run(RepaintManager.java:842)
    at javax.swing.RepaintManager$4.run(RepaintManager.java:814)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:814)
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:789)
    at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:738)
    at javax.swing.RepaintManager.access$1200(RepaintManager.java:64)
    at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1732)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:756)
    at java.awt.EventQueue.access$500(EventQueue.java:97)
    at java.awt.EventQueue$3.run(EventQueue.java:709)
    at java.awt.EventQueue$3.run(EventQueue.java:703)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:726)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

Answer 1

从 cmets 中发布的堆栈跟踪来看，下面的行似乎正在抛出异常：

colorList = new JList<String>(chooser.getKeySet().toArray(new String[0]));

chooser.getKeySet() 正在返回一个null 对象，因此，在空对象上调用toArray 会引发异常。下面是getKeySet()的实现：

public Collection<Object> getKeySet() {
    return null;
}

在理想情况下，它应该返回什么取决于类/模块的功能。但是，如果我们想防止异常，那么我们可以使用以下实现（顺便说一句，它只是返回一个空列表）：

public Collection<Object> getKeySet() {
    return Collections.<Object>emptyList();
}