What is this strange syntax in the package com.sun.tools.javac.code (javac compiler) and how does it work?

Question

I was looking at some of the internal javac sun compiler API source and came across this in the Types class:

public Boolean visitTypeVar(TypeVar var1, Type var2) {
         switch(null.$SwitchMap$com$sun$tools$javac$code$TypeTag[var2.getTag().ordinal()]) {
         case 12:
            if(Types.this.isSubtype(var1, var2)) {
               return Boolean.valueOf(true);
            } else {
               if(Types.this.isCastable(var1.bound, var2, Types.this.noWarnings)) {
                  ((Warner)Types.this.warnStack.head).warn(LintCategory.UNCHECKED);
                  return Boolean.valueOf(true);
               }

               return Boolean.valueOf(false);
            }
         case 13:
         case 16:
            return Boolean.valueOf(true);
         case 14:
         case 15:
         default:
            return Boolean.valueOf(Types.this.isCastable(var1.bound, var2, (Warner)Types.this.warnStack.head));
         }
      }

It's the second line that was interesting at this statement:

null.$SwitchMap$com$sun$tools$javac$code$TypeTag[var2.getTag().ordinal()]

Which looks like it returns an integer. How does this work?

Answer 1

This is just some fancy artifact of your decompiler.

If you look at the same code in source code form (http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/8-b132/com/sun/tools/javac/code/Types.java#1658) it is just a switch statement on an enum:

        @Override
        public Boolean visitTypeVar(TypeVar t, Type s) {
            switch (s.tag) {
            case ERROR:
            case BOT:
                return true;
            case TYPEVAR:
                if (isSubtype(t, s)) {
                    return true;
                } else if (isCastable(t.bound, s, Warner.noWarnings)) {
                    warnStack.head.warn(LintCategory.UNCHECKED);
                    return true;
                } else {
                    return false;
                }
            default:
                return isCastable(t.bound, s, warnStack.head);
            }
        }