Array Length: should I use parenthesis or not?

I'm a little bit confused about this piece of code (I didn't create it : I've taken it from a tutorial):

public String findLongestName(String[] names){
    int size = names.length;
    String longestName = names[0];

    for(int i=1; i<size; i++) {
        if(names[i].length() > longestName.length()) {
            longestName = names[i];
        }
    }

    return longestName;
}

Maybe this is a very trivial question, but I'm still a beginner in Java programming language. In particular, why is "names.length" written without parentheses when storing the length into the variable "size" ? Why should we use parentheses, instead, inside of the "if" function?

In other words, why is it incorrect to write this:

int size = names.length(); instead of "int size = names.length;"

or this:

if(names[i].length > longestName.length) instead of "if(names[i].length() > longestName.length())"

?