java - Why javac sometimes creates unnecessary copies of variables? -

java - Why javac sometimes creates unnecessary copies of variables? -

i have code looks this:

boolean[] array = new boolean[200]; int[] indexes = {10, 42, 62, 74}; while(true) { //some code here stringbuilder sb = new stringbuilder(); (int j : indexes) { sb.append(array[j] ? '1' : '0'); } }

bytecode this:

astore 3 //"indexes" array ... aload 3 astore 8 aload 8 arraylength ...

i not sure why javac re-create ref array local var.

the for-each loop converted this:

{ int[] hidden_array_ref = indexes; int hidden_length = hidden_array_ref.length; for(int hidden_counter = 0; hidden_counter < hidden_length; hidden_counter++) { int j = hidden_array_ref[hidden_counter]; sb.append(array[j] ? '1' : '0'); } }

in particular, notice int[] hidden_array_ref = indexes;. that's re-create asking about.

the compiler way if write like:

for(int j : indexes) { indexes = new int[0]; sb.append(array[j] ? '1' : '0'); }

the assignment indexes doesn't impact loop.

java javac bytecode