Increasing / Decreasing Size Of Array

I am trying to make a code that copies the users String to a char array. However, I am in a predicament: since I would not know the exact size of the users String I am left with the options of either making my array large by default, filled in with, lets say 25, empty spaces per index OR starting out with a default size of 1, with an empty space, and then some how increase the size from there.

At this moment I am leaning on the first option, creating a large default array and then deleting the unused values. However, this brings me to my actual question: if I set the non used indexes to null, if that wont give me an error, would that change the size of my array?

Ex:
//lets say i finally copied all of the values and this is the result
char[] word = {'b', 'o', 'b', ' ', ' '};
for(int i = word.length(); i > 0; i--){
if(word[i] == ' ')//delete the value so the size decreases
word[i] = null;//if possible
}