title: Java 8 compiler bug with Stream and reduce
body: <p>I am writing a small program to generate some random numbers and wanted to get statistical information about them. I have a <code>List&lt;AtomicInteger&gt;</code> that I want to use for outputting some information.</p>
  
  <p>I tried using following code to reduce the list to its total (e.g. the sum of the values of all the AtomicIntegers):</p>
  
  <pre><code>// not my real initialization code, just for illustration purposes
  List&lt;AtomicInteger&gt; values = new ArrayList&lt;&gt;();
  for(int i = 0; i &lt; 10; i++) {
      values.add(new AtomicInteger());
  }
  
  // this is the problematic reduce
  int total = values
      .parallelStream()
      .reduce(0, 
          (currentValue, currentAtomic) 
              -&gt; currentValue + currentAtomic.get(),
          (combiner1, combiner2) -&gt; combiner1 + combiner2);
  </code></pre>
  
  <p>My IDE (IntelliJ) has no problems with this line at all but with my current <code>javac</code> version (1.8.0_31) this line results in a NullPointerException in the compiler:</p>
  
  <pre><code>An exception has occurred in the compiler (1.8.0_31). 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.NullPointerException
      at com.sun.tools.javac.code.Types.isConvertible(Types.java:290)
      at com.sun.tools.javac.comp.Check.assertConvertible(Check.java:922)
      at com.sun.tools.javac.comp.Check.checkMethod(Check.java:876)
      at com.sun.tools.javac.comp.Attr.checkMethod(Attr.java:3838)
      at com.sun.tools.javac.comp.Attr.checkIdInternal(Attr.java:3615)
      at com.sun.tools.javac.comp.Attr.checkMethodIdInternal(Attr.java:3522)
      at com.sun.tools.javac.comp.Attr.checkMethodId(Attr.java:3501)
      at com.sun.tools.javac.comp.Attr.checkId(Attr.java:3488)
      at com.sun.tools.javac.comp.Attr.visitSelect(Attr.java:3370)
      at com.sun.tools.javac.tree.JCTree$JCFieldAccess.accept(JCTree.java:1897)
      at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:607)
      at com.sun.tools.javac.comp.Attr.visitApply(Attr.java:1843)
      at com.sun.tools.javac.tree.JCTree$JCMethodInvocation.accept(JCTree.java:1465)
      at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:607)
      at com.sun.tools.javac.comp.Attr.attribExpr(Attr.java:649)
      at com.sun.tools.javac.comp.Attr.visitVarDef(Attr.java:1093)
      at com.sun.tools.javac.tree.JCTree$JCVariableDecl.accept(JCTree.java:852)
      at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:607)
      at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:676)
      at com.sun.tools.javac.comp.Attr.attribStats(Attr.java:692)
      at com.sun.tools.javac.comp.Attr.visitBlock(Attr.java:1142)
      at com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:909)
      at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:607)
      at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:676)
      at com.sun.tools.javac.comp.Attr.visitMethodDef(Attr.java:1035)
      at com.sun.tools.javac.tree.JCTree$JCMethodDecl.accept(JCTree.java:778)
      at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:607)
      at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:676)
      at com.sun.tools.javac.comp.Attr.attribClassBody(Attr.java:4342)
      at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:4252)
      at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:4181)
      at com.sun.tools.javac.comp.Attr.attrib(Attr.java:4156)
      at com.sun.tools.javac.main.JavaCompiler.attribute(JavaCompiler.java:1248)
      at com.sun.tools.javac.main.JavaCompiler.compile2(JavaCompiler.java:901)
      at com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:860)
      at com.sun.tools.javac.main.Main.compile(Main.java:523)
      at com.sun.tools.javac.main.Main.compile(Main.java:381)
      at com.sun.tools.javac.main.Main.compile(Main.java:370)
      at com.sun.tools.javac.main.Main.compile(Main.java:361)
      at com.sun.tools.javac.Main.compile(Main.java:56)
      at com.sun.tools.javac.Main.main(Main.java:42)
  </code></pre>
  
  <p>I know that there are probably other ways to accomplish the same reduce, but I would really like to retain the parallel nature of the stream (since my original code has a lot of values). Can anyone suggest me another parallel reduce option that will not crash my compiler and can accomplish the same result?</p>
  
  <p>I would also like to know if this is just a problem I'm encountering or if other people can reproduce this compiler bug.</p>