簡単な質問があります。パラメータをコンストラクタに渡して新しいインスタンスを作成するにはどうすればよいですか? GraphicObject はそれを拡張するクラスのいずれかになる可能性があるため、それがどのクラスであるかを何らかの方法で知る必要があり、ここではそれを拡張するクラスを使用する必要があるため、リフレクションを試みていますが、これまでのところ null 例外のみです。
GraphicObject decor = null;
try {
decor = decorator.getClass().getDeclaredConstructor(GraphicObject.class).newInstance(mainGroup);
} catch (Exception e) {
System.out.println(e);
}
反映されるクラスは次のようになります。
public class DecoratorLeft extends GraphicObjectDecorator {
// jei bus klaida, tai bus del to, kad neuzsaugom per konstruktoriu paduodamos reiksmes i global variable
GraphicObject decoratedGraphic = null;
public DecoratorLeft(GraphicObject decoratedGraphic) {
super(decoratedGraphic);
this.decoratedGraphic = decoratedGraphic;
}
@Override
public void draw(Graphics g, AlignStrategy align) {
alignLeft();
decoratedGraphic.draw(g, align);
//drawAlignedLeft(g, decoratedGraphic, align);
}
}
エラーメッセージは次のとおりです。
java.lang.NullPointerException
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at objprog1.Whiteboard.paintComponent(Whiteboard.java:157)
printstactrace と runtimeexception を使用して、try/catch ステートメントを再度変更しました。
java.lang.NullPointerException
at objprog1.Whiteboard.paintComponent(Whiteboard.java:179)
at javax.swing.JComponent.paint(JComponent.java:1054)
at javax.swing.JComponent.paintChildren(JComponent.java:887)
at javax.swing.JSplitPane.paintChildren(JSplitPane.java:1047)
at javax.swing.JComponent.paint(JComponent.java:1063)
at javax.swing.JComponent.paintChildren(JComponent.java:887)
at javax.swing.JComponent.paint(JComponent.java:1063)
at javax.swing.JComponent.paintChildren(JComponent.java:887)
at javax.swing.JComponent.paint(JComponent.java:1063)
at javax.swing.JLayeredPane.paint(JLayeredPane.java:585)
at javax.swing.JComponent.paintChildren(JComponent.java:887)
at javax.swing.JComponent.paintToOffscreen(JComponent.java:5228)
at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(RepaintManager.java:1482)
at javax.swing.RepaintManager$PaintManager.paint(RepaintManager.java:1413)
at javax.swing.RepaintManager.paint(RepaintManager.java:1206)
at javax.swing.JComponent.paint(JComponent.java:1040)
at java.awt.GraphicsCallback$PaintCallback.run(GraphicsCallback.java:39)
at sun.awt.SunGraphicsCallback.runOneComponent(SunGraphicsCallback.java:78)
at sun.awt.SunGraphicsCallback.runComponents(SunGraphicsCallback.java:115)
at java.awt.Container.paint(Container.java:1967)
at java.awt.Window.paint(Window.java:3867)
at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:781)
at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:728)
at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:677)
at javax.swing.RepaintManager.access$700(RepaintManager.java:59)
at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1621)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:705)
at java.awt.EventQueue.access$000(EventQueue.java:101)
at java.awt.EventQueue$3.run(EventQueue.java:666)
at java.awt.EventQueue$3.run(EventQueue.java:664)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:675)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:211)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:128)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:117)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:113)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:90)
Exception in thread "AWT-EventQueue-0" java.lang.RuntimeException: java.lang.NullPointerException
at objprog1.Whiteboard.paintComponent(Whiteboard.java:182)
at javax.swing.JComponent.paint(JComponent.java:1054)
at javax.swing.JComponent.paintChildren(JComponent.java:887)
at javax.swing.JSplitPane.paintChildren(JSplitPane.java:1047)
at javax.swing.JComponent.paint(JComponent.java:1063)
at javax.swing.JComponent.paintChildren(JComponent.java:887)
at javax.swing.JComponent.paint(JComponent.java:1063)
at javax.swing.JComponent.paintChildren(JComponent.java:887)
at javax.swing.JComponent.paint(JComponent.java:1063)
at javax.swing.JLayeredPane.paint(JLayeredPane.java:585)
at javax.swing.JComponent.paintChildren(JComponent.java:887)
at javax.swing.JComponent.paintToOffscreen(JComponent.java:5228)
at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(RepaintManager.java:1482)
at javax.swing.RepaintManager$PaintManager.paint(RepaintManager.java:1413)
at javax.swing.RepaintManager.paint(RepaintManager.java:1206)
at javax.swing.JComponent.paint(JComponent.java:1040)
at java.awt.GraphicsCallback$PaintCallback.run(GraphicsCallback.java:39)
at sun.awt.SunGraphicsCallback.runOneComponent(SunGraphicsCallback.java:78)
at sun.awt.SunGraphicsCallback.runComponents(SunGraphicsCallback.java:115)
at java.awt.Container.paint(Container.java:1967)
at java.awt.Window.paint(Window.java:3867)
at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:781)
at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:728)
at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:677)
at javax.swing.RepaintManager.access$700(RepaintManager.java:59)
at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1621)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:705)
at java.awt.EventQueue.access$000(EventQueue.java:101)
at java.awt.EventQueue$3.run(EventQueue.java:666)
at java.awt.EventQueue$3.run(EventQueue.java:664)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:675)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:211)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:128)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:117)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:113)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:90)
Caused by: java.lang.NullPointerException
at objprog1.Whiteboard.paintComponent(Whiteboard.java:179)
... 39 more