After loading and casting the parserClass in TestRig#process using
`cl.loadClass(parserName).asSubclass(Parser.class)` there is a check if
the class returned by `#asSubclass` is not null:
```
parserClass = cl.loadClass(parserName).asSubclass(Parser.class);
if ( parserClass==null ) {
System.err.println("Can't load "+parserName);
}
```
The method `#asSubclass` will never return `null`, but throw an
`ClassCastException` when the cast is not valid, therefore the check
can be removed.
See also: [TestRig#process Documentation](http://docs.oracle.com/javase/6/docs/api/java/lang/Class.html#asSubclass(java.lang.Class\))
The `selectedTree.getSelectionPath()` return null if nothing is selected.
Added check to avoid NPE:
```java
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at org.antlr.v4.gui.TreeViewer$4.valueChanged(TreeViewer.java:376)
at javax.swing.JTree.fireValueChanged(JTree.java:2921)
at javax.swing.JTree$TreeSelectionRedirector.valueChanged(JTree.java:3382)
at javax.swing.tree.DefaultTreeSelectionModel.fireValueChanged(DefaultTreeSelectionModel.java:635)
at javax.swing.tree.DefaultTreeSelectionModel.notifyPathChange(DefaultTreeSelectionModel.java:1093)
at javax.swing.tree.DefaultTreeSelectionModel.removeSelectionPaths(DefaultTreeSelectionModel.java:502)
at javax.swing.JTree.removeDescendantSelectedPaths(JTree.java:3714)
at javax.swing.JTree.setExpandedState(JTree.java:3597)
at javax.swing.JTree.collapsePath(JTree.java:2231)
at javax.swing.plaf.basic.BasicTreeUI.toggleExpandState(BasicTreeUI.java:2297)
at javax.swing.plaf.basic.BasicTreeUI.handleExpandControlClick(BasicTreeUI.java:2273)
at javax.swing.plaf.basic.BasicTreeUI.checkForClickInExpandControl(BasicTreeUI.java:2231)
at javax.swing.plaf.basic.BasicTreeUI$Handler.handleSelection(BasicTreeUI.java:3600)
at javax.swing.plaf.basic.BasicTreeUI$Handler.mousePressed(BasicTreeUI.java:3548)
at java.awt.Component.processMouseEvent(Component.java:6524)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6292)
at java.awt.Container.processEvent(Container.java:2234)
at java.awt.Component.dispatchEventImpl(Component.java:4883)
at java.awt.Container.dispatchEventImpl(Container.java:2292)
at java.awt.Component.dispatchEvent(Component.java:4705)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4898)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4530)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4462)
at java.awt.Container.dispatchEventImpl(Container.java:2278)
at java.awt.Window.dispatchEventImpl(Window.java:2739)
at java.awt.Component.dispatchEvent(Component.java:4705)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:746)
at java.awt.EventQueue.access$400(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:697)
at java.awt.EventQueue$3.run(EventQueue.java:691)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.awt.EventQueue$4.run(EventQueue.java:719)
at java.awt.EventQueue$4.run(EventQueue.java:717)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:716)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)
```
The help and error message from the TestRig program refers to the old `runtime.misc` instead of the new `gui` package:
```
java org.antlr.v4.runtime.misc.TestRig GrammarName startRuleName
[-tokens] [-tree] [-gui] [-ps file.ps] [-encoding encodingname]
[-trace] [-diagnostics] [-SLL]
[input-filename(s)]
Use startRuleName='tokens' if GrammarName is a lexer grammar.
Omitting input-filename makes rig read from stdin.
```
Terence Parr
Udo Borkowski
Terence Parr
Michael Peyton Jones
Eric Vergnaud
HSorensen