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PONullPointerException in the middle of GridWorld code
 

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    <p>I am using the <a href="http://gridworld.info" rel="nofollow noreferrer">GridWorld</a> case study. I seem to have discovered a bug in the provided program. After attempting to create a grid of invalid size through the GUI and closing the error message, whenever I try to do anything with the existing grid, I get a NullPointerException:</p> <pre><code>Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at info.gridworld.gui.GUIController$3.mousePressed(GUIController.java:119) at java.awt.AWTEventMulticaster.mousePressed(AWTEventMulticaster.java:279) at java.awt.Component.processMouseEvent(Component.java:6501) at javax.swing.JComponent.processMouseEvent(JComponent.java:3321) at java.awt.Component.processEvent(Component.java:6269) at java.awt.Container.processEvent(Container.java:2229) at java.awt.Component.dispatchEventImpl(Component.java:4860) at java.awt.Container.dispatchEventImpl(Container.java:2287) at java.awt.Component.dispatchEvent(Component.java:4686) at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832) at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4489) at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422) at java.awt.Container.dispatchEventImpl(Container.java:2273) at java.awt.Window.dispatchEventImpl(Window.java:2713) at java.awt.Component.dispatchEvent(Component.java:4686) at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:707) 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.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87) at java.awt.EventQueue$4.run(EventQueue.java:680) at java.awt.EventQueue$4.run(EventQueue.java:678) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76) at java.awt.EventQueue.dispatchEvent(EventQueue.java:677) at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThre ad.java:211) at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread. java:128) at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThre ad.java:117) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:113) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:105) at java.awt.EventDispatchThread.run(EventDispatchThread.java:90) </code></pre> <p>Additionally, I am unable to change the grid to something else, via the provided GUI:</p> <pre><code>Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at info.gridworld.gui.WorldFrame.setGrid(WorldFrame.java:237) at info.gridworld.gui.MenuMaker$GridConstructorItem.actionPerformed(MenuMaker.java:344) at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018) at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341) at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402) at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259) at javax.swing.AbstractButton.doClick(AbstractButton.java:376) at javax.swing.plaf.basic.BasicMenuItemUI.doClick(BasicMenuItemUI.java:833) at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(BasicMenuItemUI.java:877) at java.awt.Component.processMouseEvent(Component.java:6504) at javax.swing.JComponent.processMouseEvent(JComponent.java:3321) at java.awt.Component.processEvent(Component.java:6269) at java.awt.Container.processEvent(Container.java:2229) at java.awt.Component.dispatchEventImpl(Component.java:4860) at java.awt.Container.dispatchEventImpl(Container.java:2287) at java.awt.Component.dispatchEvent(Component.java:4686) at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832) at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492) at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422) at java.awt.Container.dispatchEventImpl(Container.java:2273) at java.awt.Window.dispatchEventImpl(Window.java:2713) at java.awt.Component.dispatchEvent(Component.java:4686) at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:707) 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.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87) at java.awt.EventQueue$4.run(EventQueue.java:680) at java.awt.EventQueue$4.run(EventQueue.java:678) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76) at java.awt.EventQueue.dispatchEvent(EventQueue.java:677) 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) </code></pre> <p>I think this is a bug in the GridWorld program itself, and not in any code I write, because this seems to happen even when I just launch the program without giving it any code to execute. I've done some investigation and found that for some reason, the grid gets set to <code>null</code> whenever I attempt to change the grid in the GUI, and the grid I try to create is invalid (or any exception happens when creating the grid). Why is the grid getting set to <code>null</code>? Is there a way I can fix this in the provided source code myself?</p> <p>The build that I am using is GridWorld 1.02 available at GridWorld.info under the "unofficial code" link. The code at the CollegeBoard website is older. I've tested this and it <em>also</em> happens for older releases.</p>
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    1. COStart with `GUIController.java:119` maybe and work out what's `null` any why.
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    2. CO@bmorris591 For some reason, World.getGrid() is returning null. Have you tried testing it?
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