int[] arr = {1,2,3,4,5,6,7,8,9};
String a = "";
for(int i = 0; i < arr.length; i++){
a += Integer.toString(arr[i]);
}
System.out.println(Integer.parseInt(a));
int[] array = {1,8,2,3,4,5,6,7,8,9};
int mul = 1, sum = 0;
for( int i = array.length-1; i >= 0; i-- ) {
sum += mul * array[i];
mul *= 10;
}