in checkForSum change
if (abundant.get(start) == num) {
return true; // not false
}
and remove
else if (abundant.get(end) == num) {
...
}
try
public static boolean checkForSum(int num) {
int start = 0;
int end = abundant.size() - 1;
while (start < end) {
if (abundant.get(start) == num) {
return true;
}
else if (abundant.get(start)*2 == num) {
return false;
}
else if (abundant.get(end)*2 == num) {
return false;
}
else if (abundant.get(start) + abundant.get(end) == num) {
return false;
}
else if (abundant.get(start) + abundant.get(end) < num) {
start++;
}
else if (abundant.get(start) + abundant.get(end) > num) {
end--;
}
}
return true;
}