What is

<-- is not a new Java operator (even though it may look like it), but there are 2 normal operators: < and --

while (var2 <-- var1) is the same as while(var2 < (--var1)), which can be translated to plain english as:

1. decrement the var1 variable ( --var is a prefix decrementation, ie. decrement the variable before condition validation)
2. Validate the condition var2 < var1