question: public static long [ ] join ( long [ ] arrayA , long ... arrayB ) { if ( ( arrayB == null ) || ( arrayB . length == 0 ) ) { return arrayA ; } if ( ( arrayA == null ) || ( arrayA . length == 0 ) ) { return arrayB ; } long [ ] array = new long [ arrayA . length + arrayB . length ] ; System . arraycopy ( arrayA , 0 , array , 0 , arrayA . length ) ; System . arraycopy ( arrayB , 0 , array , arrayA . length , arrayB . length ) ; return array ; }
target:  Joins 2 arrays together, if any array is null or empty then other array will be retuned without coping anything.