Why does javac checkcast arrays twice?

Examining bytecode, I've noticed javac seems to duplicate `checkcast` instructions when casting to array types. Cast.java: ``` class Cast { void test(Object a) { Object[] b = (Object[]) a; } } ``` javap disassembly of the javac compiled version ``` void test(java.lang.Object); Code: 0: aload_1 1: checkcast #2; //class "[Ljava/lang/Object;" 4: checkcast #2; //class "[Ljava/lang/Object;" 7: astore_2 8: return ``` Testing jikes shows the expected single cast ``` void test(java.lang.Object); Code: 0: aload_1 1: checkcast #10; //class "[Ljava/lang/Object;" 4: astore_2 5: return ``` `checkcast` is supposed to raise an exception if the object can't be treated as the requested type and otherwise does nothing, so I don't see why it might help to double the cast. I haven't looked at the JDK sources to see how it's produced, and if that helps explain the why (maybe it's meant as a hint).