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我有两台显示器
我编写了非常小的 Swing Java 代码来收集所有屏幕设备的信息，通过在控制面板中设置显示来改变显示模式和一个或两个显示屏幕。和如下代码：

import java.awt.GraphicsDevice;
import java.awt.GraphicsEnvironment;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;


public class Main {

    public static void main(String[] args) {
        final JFrame frame = new JFrame("Demo get info screen devices");
        JButton button = new JButton("Print info screen devices");
        button.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                printInfoAllScreenDevices();
            }
        });
        frame.add(button);
        frame.setSize(500, 300);
        frame.setVisible(true);
    }
    private static void printInfoAllScreenDevices() {
        GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
        GraphicsDevice[] graphicsDevices = ge.getScreenDevices();
        System.out.println("Number of screen devices:" + graphicsDevices.length);
    }
}

首先，我用两个屏幕启动程序，然后单击按钮（“打印信息屏幕设备”）。在输出显示

Number of screen devices:2

正确的！
接下来我更改为一种显示模式。最后，再次单击按钮，结果仍然是 2。实际上只有 1 个屏幕设备。
我检查 GraphicsEnvironment.getLocalGraphicsEnvironment() 创建一个像单例这样的实例。意思是不能更新？还有一件事，我不想关闭程序并再次打开。
我怎样才能获得像这种情况下的屏幕设备的正确信息？
而且我还希望Java决定哪个类（扩展GraphicsEnvironment）提供屏幕设备的信息，取决于操作系统。
感谢您的提前！

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1 回答 1

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这可能很棘手。但是通过快速查看源代码，您可能会尝试一些反思。

免责声明：使用反射时，很多事情都可能出错。您应该意识到您在此处依赖未指定的行为这一事实。如果底层实现发生变化，那么下面的示例程序可能不再工作......

...虽然我认为这是“不太可能”，至少

下面是一个例子，展示了它是如何工作的：

import java.awt.GraphicsDevice;
import java.awt.GraphicsEnvironment;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;

public class GraphicsEnvironmentTest
{
    public static void main(String[] args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            @Override
            public void run()
            {
                createAndShowGUI();
            }
        });
    }

    private static void createAndShowGUI()
    {
        JFrame frame = new JFrame("Demo get info screen devices");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JButton button = new JButton("Print info screen devices");
        button.addActionListener(new ActionListener()
        {

            @Override
            public void actionPerformed(ActionEvent e)
            {
                printInfoAllScreenDevices();
            }
        });
        frame.add(button);
        frame.setSize(500, 300);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    private static void printInfoAllScreenDevices() 
    {
        GraphicsDevice graphicsDevices[] = getGraphicsDevices();
        System.out.println("Found "+graphicsDevices.length+" devices:");
        for (int i=0; i<graphicsDevices.length; i++)
        {
            System.out.println(graphicsDevices[i]);
        }
    }

    /**
     * Queries the local graphics environment for the available graphics
     * devices. This uses reflection internally. If anything goes wrong
     * with the reflective call, a RuntimeException will be thrown.
     * 
     * @return The available graphics devices.
     * @throws RuntimeException If the reflective calls fail
     */
    private static GraphicsDevice[] getGraphicsDevices() 
    {
        GraphicsEnvironment graphicsEnvironment = 
            GraphicsEnvironment.getLocalGraphicsEnvironment();
        Class<?> c = graphicsEnvironment.getClass();
        Method getNumScreensMethod = null;
        boolean getNumScreensMethodWasAccessible = false; 
        Method makeScreenDeviceMethod = null;
        boolean makeScreenDeviceMethodWasAccessible = false;
        try
        {
            getNumScreensMethod = 
                c.getDeclaredMethod("getNumScreens");
            getNumScreensMethodWasAccessible =
                getNumScreensMethod.isAccessible();
            getNumScreensMethod.setAccessible(true);

            makeScreenDeviceMethod = 
                c.getDeclaredMethod("makeScreenDevice", int.class);
            makeScreenDeviceMethodWasAccessible =
                makeScreenDeviceMethod.isAccessible();
            makeScreenDeviceMethod.setAccessible(true);

            int numScreens = 
                (Integer) getNumScreensMethod.invoke(graphicsEnvironment);
            GraphicsDevice graphicsDevices[] = new GraphicsDevice[numScreens];
            for (int i = 0; i < numScreens; i++)
            {
                Object object = 
                    makeScreenDeviceMethod.invoke(graphicsEnvironment, i);
                graphicsDevices[i] = (GraphicsDevice) object;
            }
            return graphicsDevices;
        }
        catch (NoSuchMethodException e)
        {
            throw new RuntimeException(e);
        }
        catch (SecurityException e)
        {
            throw new RuntimeException(e);
        }
        catch (IllegalAccessException e)
        {
            throw new RuntimeException(e);
        }
        catch (IllegalArgumentException e)
        {
            throw new RuntimeException(e);
        }
        catch (InvocationTargetException e)
        {
            throw new RuntimeException(e);
        }
        finally
        {
            if (getNumScreensMethod != null)
            {
                getNumScreensMethod.setAccessible(
                    getNumScreensMethodWasAccessible);
            }
            if (makeScreenDeviceMethod != null)
            {
                makeScreenDeviceMethod.setAccessible(
                    makeScreenDeviceMethodWasAccessible);
            }
        }
    }

}
于 2014-11-13T16:19:21.950 回答