simplified boundary checking for Java List

Question

Is there an easy way/library to check and adjust parameters to stay inside the lists boundaries?

Here a long sample:

if (fromIndex < 0) {
  fromIndex = 0;
}
if (fromIndex > list.size() - 1) {
  fromIndex = list.size() - 1;
}

if (toIndex < 0) {
  toIndex = 0;
}
if (toIndex > list.size() - 1) {
  toIndex = list.size() - 1;
}

list.subList(fromIndex, toIndex);

I know i could move list.size() - 1 to a variable and do an extract-method on the index checks to remove redundant code. But it still seems a bit verbose for this simple task.

Answer 1

public int sanitize(int index) {
  return Math.max(0, Math.min(index, this.length-1));
}

Answer 2

If you want to check all accesses to your list, it seems to me you want to wrap your list within a class implementing the List interface and intercept the accessor methods to check/modify the accessor indices.

e.g.

List sanitised = new SanitisedList(existingList);

This is an example of the Decorator pattern. Note how you just need one class defined (SanitisedList) and you can apply that to any list you have. Use Zed's answer for a nice tidy bounds check.

Answer 3

You could use the ternary operator:

int listMax = list.size() - 1;
list.subList( fromIndex < 0 ? 0 : (fromIndex > listMax) ? listMax : fromIndex, 
              toIndex < 0 ? 0 : (toIndex > listMax) ? listMax : toIndex );