Just wondering….

Yesterday was a red letter day. I found multiple bugs in the javac and javadoc. (1.6.0_17)

This javadoc issue occurred when there is a class that has no package line ( it is in the default package). Annoyingly enough it occurred when I was trying to create a test case for this javac bug. I was running maven 2.2.1 at the time.

java.lang.NullPointerException
       at com.sun.tools.doclets.formats.html.PackageUseWriter.generatePackageUse(PackageUseWriter.java:180)
       at com.sun.tools.doclets.formats.html.PackageUseWriter.generatePackageList(PackageUseWriter.java:124)
       at com.sun.tools.doclets.formats.html.PackageUseWriter.generatePackageUse(PackageUseWriter.java:110)
       at com.sun.tools.doclets.formats.html.PackageUseWriter.generatePackageUseFile(PackageUseWriter.java:99)
       at com.sun.tools.doclets.formats.html.PackageUseWriter.generate(PackageUseWriter.java:78)
       at com.sun.tools.doclets.formats.html.ClassUseWriter.generate(ClassUseWriter.java:116)
       at com.sun.tools.doclets.formats.html.HtmlDoclet.generateOtherFiles(HtmlDoclet.java:92)
       at com.sun.tools.doclets.internal.toolkit.AbstractDoclet.startGeneration(AbstractDoclet.java:122)
       at com.sun.tools.doclets.internal.toolkit.AbstractDoclet.start(AbstractDoclet.java:64)
       at com.sun.tools.doclets.formats.html.HtmlDoclet.start(HtmlDoclet.java:42)
       at com.sun.tools.doclets.standard.Standard.start(Standard.java:23)
       at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
       at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
       at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
       at java.lang.reflect.Method.invoke(Method.java:597)
       at com.sun.tools.javadoc.DocletInvoker.invoke(DocletInvoker.java:269)
       at com.sun.tools.javadoc.DocletInvoker.start(DocletInvoker.java:143)
       at com.sun.tools.javadoc.Start.parseAndExecute(Start.java:340)
       at com.sun.tools.javadoc.Start.begin(Start.java:128)
       at com.sun.tools.javadoc.Main.execute(Main.java:41)
       at com.sun.tools.javadoc.Main.main(Main.java:31)

Solution was to put the java code into a package.

My javac crash:

An exception has occurred in the compiler (1.6.0_17). Please file a bug at the Java Developer Connection (http://java.sun.com/webapps/bugreport) after checking the Bug Parade for duplicates. Include your program and the following diagnostic in your report. Thank you.

java.lang.AssertionError: isSubtype 15 ( 15 = TypeTags.WILDCARD )
	at com.sun.tools.javac.code.Types$5.visitType(Types.java:347)
	at com.sun.tools.javac.code.Types$5.visitType(Types.java:328)
	at com.sun.tools.javac.code.Types$DefaultTypeVisitor.visitWildcardType(Types.java:3163)
	at com.sun.tools.javac.code.Type$WildcardType.accept(Type.java:416)
	at com.sun.tools.javac.code.Types$DefaultTypeVisitor.visit(Types.java:3161)
	at com.sun.tools.javac.code.Types.isSubtype(Types.java:324)
	at com.sun.tools.javac.code.Types.isSubtype(Types.java:308)
	at com.sun.tools.javac.code.Types.isSubtypeUnchecked(Types.java:288)
	at com.sun.tools.javac.code.Types.isSubtypeUnchecked(Types.java:460)
	at com.sun.tools.javac.comp.Infer.checkWithinBounds(Infer.java:388)
	at com.sun.tools.javac.comp.Infer.instantiateExpr(Infer.java:241)
	at com.sun.tools.javac.comp.Check.instantiatePoly(Check.java:356)
	at com.sun.tools.javac.comp.Check.checkType(Check.java:324)
	at com.sun.tools.javac.comp.Attr.check(Attr.java:160)
	at com.sun.tools.javac.comp.Attr.visitApply(Attr.java:1276)
	at com.sun.tools.javac.tree.JCTree$JCMethodInvocation.accept(JCTree.java:1210)
	at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:360)
	at com.sun.tools.javac.comp.Attr.attribExpr(Attr.java:377)
	at com.sun.tools.javac.comp.Attr.visitAssign(Attr.java:1550)
	at com.sun.tools.javac.tree.JCTree$JCAssign.accept(JCTree.java:1342)
	at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:360)
	at com.sun.tools.javac.comp.Attr.attribExpr(Attr.java:384)
	at com.sun.tools.javac.comp.Attr.visitExec(Attr.java:1017)
	at com.sun.tools.javac.tree.JCTree$JCExpressionStatement.accept(JCTree.java:1074)
	at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:360)
	at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:397)
	at com.sun.tools.javac.comp.Attr.attribStats(Attr.java:413)
	at com.sun.tools.javac.comp.Attr.visitBlock(Attr.java:715)
	at com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:739)
	at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:360)
	at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:397)
	at com.sun.tools.javac.comp.Attr.visitIf(Attr.java:1009)
	at com.sun.tools.javac.tree.JCTree$JCIf.accept(JCTree.java:1050)
	at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:360)
	at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:397)
	at com.sun.tools.javac.comp.Attr.attribStats(Attr.java:413)
	at com.sun.tools.javac.comp.Attr.visitBlock(Attr.java:715)
	at com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:739)
	at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:360)
	at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:397)
	at com.sun.tools.javac.comp.Attr.visitForLoop(Attr.java:740)
	at com.sun.tools.javac.tree.JCTree$JCForLoop.accept(JCTree.java:818)
	at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:360)
	at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:397)
	at com.sun.tools.javac.comp.Attr.attribStats(Attr.java:413)
	at com.sun.tools.javac.comp.Attr.visitBlock(Attr.java:715)
	at com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:739)
	at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:360)
	at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:397)
	at com.sun.tools.javac.comp.Attr.visitIf(Attr.java:1009)
	at com.sun.tools.javac.tree.JCTree$JCIf.accept(JCTree.java:1050)
	at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:360)
	at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:397)
	at com.sun.tools.javac.comp.Attr.attribStats(Attr.java:413)
	at com.sun.tools.javac.comp.Attr.visitBlock(Attr.java:715)
	at com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:739)
	at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:360)
	at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:397)
	at com.sun.tools.javac.comp.Attr.visitIf(Attr.java:1009)
	at com.sun.tools.javac.tree.JCTree$JCIf.accept(JCTree.java:1050)
	at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:360)
	at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:397)
	at com.sun.tools.javac.comp.Attr.attribStats(Attr.java:413)
	at com.sun.tools.javac.comp.Attr.visitBlock(Attr.java:715)
	at com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:739)
	at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:360)
	at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:397)
	at com.sun.tools.javac.comp.Attr.visitMethodDef(Attr.java:634)
	at com.sun.tools.javac.tree.JCTree$JCMethodDecl.accept(JCTree.java:639)
	at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:360)
	at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:397)
	at com.sun.tools.javac.comp.Attr.attribClassBody(Attr.java:2697)
	at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:2628)
	at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:2564)
	at com.sun.tools.javac.main.JavaCompiler.attribute(JavaCompiler.java:1036)
	at com.sun.tools.javac.main.JavaCompiler.compile2(JavaCompiler.java:765)
	at com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:730)
	at com.sun.tools.javac.main.Main.compile(Main.java:353)
	at com.sun.tools.javac.main.Main.compile(Main.java:279)
	at com.sun.tools.javac.main.Main.compile(Main.java:270)
	at com.sun.tools.javac.Main.compile(Main.java:69)
	at com.sun.tools.javac.Main.main(Main.java:54)

I was not successful at reducing this crash to a simple test case.

However, the line that triggered the crash was:

Some points:

• Once again (and again) the eclipse compiler is more robust than the sun javac
• ProxyMapperImplementor is defined as:
  
  

  interface ProxyMapperImplementor<I, O extends I>

• Removing the wildcards so the line looks like solved the problem:
  

  ProxyMapperImplementor childProxy = this;

  Update (email from sun):

  This issue is related to Bug ID: 6738538. You can review this bug at:

  http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6738538

  This problem has been fixed in Java SE 7.0. Consider downloading a free copy at http://download.java.net/jdk7/binaries/ and checking if the problem persists. If the problem persists do let us know and we shall investigate this furthur.

  We greatly appreciate your efforts in identifying areas in the Java Standard Edition where we can improve upon and I would request you to continue doing so.

For some reason, the type variable <O> cannot flow through from an external caller through a callee to another called method.

This compiles just fine in eclipse, but once again sun’s javac is temperamental.

The three solutions seem to be:

1. pass an object of type <O> to the subcallee method (m0(), p0() )
2. use wildcard instead of <O> – which is o.k. if O is not needed in the body of the method
3. assign to a variable with no generic information (universal backup solution to java generic wierdness)

I filed a bug with Sun.

(Technical details: javac 1.6.0_17 )

public class Foo {
    public > I m(I i) {
/*line3*/        R r = (R) p(i);
        return i;
    }
    public > R p(I i) {
        return null;
    }

    public > I m0(O o) {
        K r= (K) p0(o);
        return o;
    }
    public > K p0(O o) {
        return null;
    }

    public > I m1(I i) {
        K r= (K) p1(i);
        return i;
    }
    public > K p1(I i) {
        return null;
    }

    public > I m2(I i) {
/*line 27*/        K r= (K) p2(i);
        return i;
    }
    public > K p2(I i) {
        return null;
    }
    interface FooInterface {

    }
}

Foo.java:3: incompatible types; inferred type argument(s) I,java.lang.Object do not conform to bounds of type variable(s) O,R
found : R
required: java.lang.Object
/*line3*/ R r = (R) p(i);
^
Foo.java:27: incompatible types; inferred type argument(s) I,java.lang.Object do not conform to bounds of type variable(s) O,K
found : K
required: java.lang.Object
K r= (K) p2(i);
^

h/t Larry Gordon (copied because I want to make sure I always have it available):

When I log into the network at my job my Mac’s hostname always turns to:

larryx.na.corp.ipgnetwork.com

I have my local hostname set to:

larryx.local

So What I would like to do is set my Mac’s hostname to my local hostname. You can do this all from Terminal in a single line.

Run this command in Terminal:

sudo scutil --set HostName larryx.local

type parameters of T cannot be determined; no unique maximal instance exists for type variable T with upper bounds T,java.lang.Object

In java 1.6u2 running in maven 2.0.7, we started getting this message but in eclipse 3.3.0 we were not. (and in idea we also were failing)

First, what the hell does this message means? Second, why can eclipse handle the issue and not the regular jdk?

Anyhow the problem was caused by this (our example was a little more complex than this):



public <T> T getFoo() {
T result;
result = getBar();
return result;
}

public <T> T getBar() {
return (T) map.get("bar");
}

The workaround is casting the line:



result = getBar();

to:



result = (T)getBar();

So I struggled for hours trying to get apache to connect via the ajp13 worker to tomcat 5.5 We are using a Debian box on the production server. Could not make it happen…. until I set the worker to be ‘ajp13′.

Don’t understand what wierdness is going on but… I do know this. if my /etc/libapache-mod-jk/workers.properties file looks like this (comments removed):

workers.tomcat_home=/usr/share/tomcat5.5
workers.java_home=/usr/local/java
worker.list=ajp13
worker.ajp13.port=8009
worker.ajp13.host=localhost
worker.ajp13.type=ajp13
worker.ajp13.lbfactor=1
worker.loadbalancer.type=lb
worker.loadbalancer.balanced_workers=ajp13

Apache 2 talks very nicely with Tomcat 5.5.20

If it looks like this:

workers.tomcat_home=/usr/share/tomcat5.5
workers.java_home=/usr/local/java
worker.list=amplafi_ajp13
worker.amplafi_ajp13.port=8009
worker.amplafi_ajp13.host=localhost
worker.amplafi_ajp13.type=ajp13
worker.amplafi_ajp13.lbfactor=1
worker.loadbalancer.type=lb
worker.loadbalancer.balanced_workers=amplafi_ajp13

Everything is broken!

Does anyone have a clue here on why?