NPE在无头(RepaintManager.currentManager)中调用新的JPanel()时 [英] NPE when calling new JPanel() in headless (RepaintManager.currentManager)
问题描述
我正在使用openjdk-8-jdk-armhf
运行一个无头的linux框,当我运行我的应用程序时,该行
I'm running a headless linux box with openjdk-8-jdk-armhf
and when I run my application, the line
METRICS = new JPanel().getFontMetrics(FONT);
引发一个NullPointerException,该异常返回到RepaintManager.currentManager(RepaintManager.java:262)
,如下所示:
Throws a NullPointerException reaching back to RepaintManager.currentManager(RepaintManager.java:262)
, which looks like this:
public static RepaintManager currentManager(Component c) {
// Note: DisplayChangedRunnable passes in null as the component, so if
// component is ever used to determine the current
// RepaintManager, DisplayChangedRunnable will need to be modified
// accordingly.
return currentManager(AppContext.getAppContext());
}
完整跟踪如下:
java.lang.NullPointerException
at javax.swing.RepaintManager.currentManager(RepaintManager.java:262)
at javax.swing.JComponent.repaint(JComponent.java:4799)
at java.awt.Component.repaint(Component.java:3303)
at javax.swing.JComponent.setFont(JComponent.java:2756)
at javax.swing.LookAndFeel.installColorsAndFont(LookAndFeel.java:208)
at javax.swing.plaf.basic.BasicPanelUI.installDefaults(BasicPanelUI.java:66)
at javax.swing.plaf.basic.BasicPanelUI.installUI(BasicPanelUI.java:56)
at javax.swing.JComponent.setUI(JComponent.java:664)
at javax.swing.JPanel.setUI(JPanel.java:153)
at javax.swing.JPanel.updateUI(JPanel.java:126)
at javax.swing.JPanel.<init>(JPanel.java:86)
at javax.swing.JPanel.<init>(JPanel.java:109)
at javax.swing.JPanel.<init>(JPanel.java:117)
at lukemoll.MyClass.<init>(MyClass.java:15)
我可以通过jsvc
和java
命令重现此错误.
I can reproduce this error both through the jsvc
and java
commands.
推荐答案
此(
Canvas
)也可以在无头模式下工作.
This (
Canvas
) will also work in headless mode.
我最终使用了new Canvas().getFontMetrics(font);
,我不确定我上次如何使它工作,但这在我的机器(tm)上有效.
I ended up using new Canvas().getFontMetrics(font);
, I'm not sure how I got it to work last time but this Works On My Machine(tm).
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