question: protected static Object [ ] concatenate ( Object [ ] a1 , Object [ ] a2 ) { int a1Len = a1 . length ; int a2Len = a2 . length ; if ( a1Len == 0 ) return a2 ; if ( a2Len == 0 ) return a1 ; Object [ ] res = new Object [ a1Len + a2Len ] ; System . arraycopy ( a1 , 0 , res , 0 , a1Len ) ; System . arraycopy ( a2 , 0 , res , a1Len , a2Len ) ; return res ; }
target:  Utility method to concatenate two arrays.