I have a question regarding Bruce Eckel's book "Thinking in Java 4th Edition"

Could you paste your build.xml?

The build.xml follows. Note, although I'm not familiar with ant, I do see the refs to j2s3 5. I guess my question is, is the books source code really compatible for java 6 or is there a problem in the build.xml.

<?xml version="1.0" ?>

<project basedir="." default="run" name="Thinking in Java, 4th Edition by Bruce Eckel">

  <description>
    Main build.xml for the source code for
    Thinking in Java, 4th Edition by Bruce Eckel
    Code available at http://www.MindView.net
    See copyright notice in CopyRight.txt

    Ant available from: http://jakarta.apache.org/ant

    To see options, type: ant -p
  </description>

  <condition property="version1.5">
    <equals arg1="1.5" arg2="${ant.java.version}"/>
  </condition>

  <filelist id="buildfiles" dir="."
    files="object/build.xml
      operators/build.xml
      control/build.xml
      initialization/build.xml
      access/build.xml
      net/build.xml
      reusing/build.xml
      polymorphism/build.xml
      interfaces/build.xml
      innerclasses/build.xml
      holding/build.xml
      exceptions/build.xml
      strings/build.xml
      typeinfo/build.xml
      generics/build.xml
      arrays/build.xml
      containers/build.xml
      io/build.xml
      xml/build.xml
      enumerated/build.xml
      annotations/build.xml
      concurrency/build.xml
      gui/build.xml
      frogbean/build.xml
      bangbean/build.xml
      swt/build.xml
      "/>

  <target name="run" description="Compiles and runs all examples">
    <delete file="errors.txt"/>
    <subant>
      <filelist refid="buildfiles"/>
    </subant>
    <available file="errors.txt" property="errors"/>
    <antcall target="finish"/>
  </target>

  <target name="build" description="Compiles all examples">
    <fail message="J2SE5 required" unless="version1.5"/>
    <delete file="errors.txt"/>
    <subant target="build">
      <filelist refid="buildfiles"/>
    </subant>
    <available file="errors.txt" property="errors"/>
    <antcall target="finish"/>
  </target>

  <target name="clean" description="delete all byproducts">
    <delete>
      <fileset dir="${basedir}" includes="**/*.class"/>
      <fileset dir="${basedir}" includes="**/*Output.txt"/>
      <fileset dir="${basedir}" includes="**/log.txt"/>
      <fileset dir="${basedir}" includes="errors.txt"/>
      <fileset dir="${basedir}" includes="failures"/>
    </delete>
    <echo message="clean successful"/>
  </target>

  <target name="finish" if="errors">
    <echo message="Errors occurred.  See errors.txt for information."/>
  </target>

  <target name="verify" depends="run"
    description="Verifies comment output; requires Python 2.3">
    <exec executable="python">
      <arg value="OutputVerifier.py"/>
    </exec>
  </target>

  <target name="findbugs" depends="build"
    description="Runs findbugs. Must install findbugs from findbugs.sourceforge.net">
    <exec executable="findbugs.bat">
      <arg value="-textui"/>
      <arg value="-sortByClass"/>
      <arg value="-exclude"/>
      <arg value="FindBugsFilter.xml"/>
      <arg value="-html"/>
      <arg value="."/>
      <redirector output="findbugs.html"/>
    </exec>
  </target>

  <target name="findbugs-plain" depends="build"
    description="Runs findbugs with plain text output">
    <exec executable="findbugs.bat">
      <arg value="-textui"/>
      <arg value="-sortByClass"/>
      <arg value="-exclude"/>
      <arg value="FindBugsFilter.xml"/>
      <arg value="."/>
      <redirector output="findbugs.txt"/>
    </exec>
  </target>

  <target name="findbugs-xml" depends="build"
    description="Runs findbugs with xml output">
    <exec executable="findbugs.bat">
      <arg value="-textui"/>
      <arg value="-sortByClass"/>
      <arg value="-exclude"/>
      <arg value="FindBugsFilter.xml"/>
      <arg value="-xml"/>
      <arg value="."/>
      <redirector output="findbugs.xml"/>
    </exec>
  </target>

</project>

try getting rid of this line:

    <fail message="J2SE5 required" unless="version1.5"/>

The source is compatible, but ant is constraining the source code to the 1.5 version. You should do what objects suggested and it would be fine =)

Actually, objects suggestion causes more errors. The line in the build following the fail message displays an error if I comment out the fail message. Since my goal is to learn Java, I think I'll just install java 1.5. It's odd that the author's web site contains no information under errata discussing this problem.

if thats the case then it sounds like it is not compatible with 1.6 so grabbing 1.5 is the way to go.

Alternatively you can try using the below line

<fail message="J2SE6 required" unless="version1.6"/>

in place of the original one
<fail message="J2SE5 required" unless="version1.5"/>

That might work.

Can you post your modified build.xml for reference ? So that we would know the solution if we faced a similar problem.