[英]What causes a NullPointerException in the AWT-EventQueue-0 thread
我正在嘗試做一些事情來查找問題,但是直到paintContents為止,我無能為力,而且調試器中的所有東西看起來都很不錯,但是我會仔細檢查以確保沒有遺漏任何東西。 至少,我想知道如何靜默處理這些錯誤(例如捕獲它們並能夠輸出有意義的錯誤消息,因為一旦拋出該錯誤,GUI就會停頓並凍結一段時間)。
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at sun.java2d.pipe.DuctusShapeRenderer.renderPath(Unknown Source)
at sun.java2d.pipe.DuctusShapeRenderer.draw(Unknown Source)
at sun.java2d.pipe.PixelToParallelogramConverter.draw(Unknown Source)
at sun.java2d.pipe.PixelToParallelogramConverter.draw(Unknown Source)
at sun.java2d.SunGraphics2D.draw(Unknown Source)
SNIP - MY CALL TO PAINT THE LAYER
at com.jhlabs.map.layer.Layer.paintContents(Layer.java:70)
at com.jhlabs.map.layer.Layer.paint(Layer.java:59)
at com.jhlabs.map.layer.Layer.paintLayers(Layer.java:76)
at com.jhlabs.map.layer.Layer.paintContents(Layer.java:68)
at com.jhlabs.map.layer.Layer.paint(Layer.java:59)
at com.jhlabs.Globe.paint(Globe.java:305)
at javax.swing.JComponent.paintChildren(Unknown Source)
at javax.swing.JComponent.paint(Unknown Source)
at javax.swing.JComponent.paintToOffscreen(Unknown Source)
at javax.swing.BufferStrategyPaintManager.paint(Unknown Source)
at javax.swing.RepaintManager.paint(Unknown Source)
at javax.swing.JComponent._paintImmediately(Unknown Source)
at javax.swing.JComponent.paintImmediately(Unknown Source)
at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
at javax.swing.RepaintManager.seqPaintDirtyRegions(Unknown Source)
at javax.swing.SystemEventQueueUtilities$ComponentWorkRequest.run(Unknow
n Source)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)
以下源代碼來自Java Map Projection Library 。
Layer.paintContents:
public void paintContents(MapGraphics g) {
if (g != null) {
paintLayers(g);
paintFeatures(g);
paintLayer(g);
}
}
Layer.paint:
public void paint(MapGraphics g) {
if (isVisible()) {
Graphics2D g2d = g.getGraphics2D();
AffineTransform saveTransform = g2d.getTransform();
Composite saveComposite = g2d.getComposite();
Projection saveProjection = g.getProjection();
Style saveStyle = g.getStyle();
if (composite != null)
g2d.setComposite(composite);
if (transform != null)
g2d.transform(transform);
if (style != null)
g.setStyle(style);
if (projection != null)
g.setProjection(projection);
paintContents(g);
g.setStyle(saveStyle);
g.setProjection(saveProjection);
g2d.setComposite(saveComposite);
g2d.setTransform(saveTransform);
}
}
Layer.paintLayers:
public void paintLayers(MapGraphics g) {
for (Iterator<Layer> it = getLayersIterator(); it.hasNext();) {
Layer l = (Layer) it.next();
l.paint(g);
}
}
Globe.paint:
public void paint(Graphics g) {
Graphics2D g2 = (Graphics2D) g;
// Turn on antialiasing - otherwise it looks horrible
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
// Put the origin at bottom left
g2.translate(0, getHeight());
g2.scale(1, -1);
// Put the globe in the middle
g2.translate(getWidth() / 2, getHeight() / 2);
Point2D.Float p = new Point2D.Float(1, 0);
transform.deltaTransform(p, p);
float rscale = 1.0f / (float) Math.sqrt(p.x * p.x + p.y * p.y);
g2.setStroke(new BasicStroke(rscale * 0.5f));
MapGraphics mg = MapGraphics.getGraphics(g2, new Rectangle(getSize()));
seaLayer.setVisible(showSea);
tissotLayer.setVisible(showTissot);
worldLayer.setVisible(showWorld);
graticuleLayer.setVisible(showGraticule);
map.paint(mg);
if (showNight) {
Color c = new Color(0, 0, 0, 0.5f);
GeneralPath gc = new GeneralPath();
ProjectionPainter.smallCircle(45, 5, 87, 180, gc, true);
gc.closePath();
ProjectionPainter pp = ProjectionPainter.getProjectionPainter(projection);
pp.drawPath(g2, gc, null, c);
}
}
我在堆棧中看到由該行定義的空白區域:
SNIP - MY CALL TO PAINT THE LAYER
該代碼稱為SunGraphics2D.draw(Shape)
。 我沒有在編輯過的代碼中看到該調用。但是,看起來好像要傳遞給SunGraphics2D.draw()
的Shape
為空。
這意味着在處理事件時(在這種情況下看起來像是重新繪制),拋出了NullPointerException。 這意味着您嘗試在對象上調用方法,結果卻為空。
com.jhlabs.map.layer.Layer類的paintContents()方法中第70行上的內容具有空引用。
我不知道您使用的是哪個IDE,但是在Eclipse中,您可以告訴調試器打破特定類型的異常,例如NPE。
您可以在啟用此選項的情況下在Debugmodus中運行您的App,然后嘗試重現該錯誤,以便可以在Debugger中檢查出了什么問題。
檢查sun lib的源代碼是否可用。 如果是這樣:指示調試器在引發NPE時保持執行。 然后,您可以檢查為空的對象並猜測(或回溯)該引用中應包含哪個對象
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