Question

I hope this is a very simple question, what is the Android equivalent to doing this in PHP:

PHP:

function BlahBlah ($first_var,$second_var,$optional_var_1=null,$optional_var_2=null) {

}

In Android it appears everything I feed into a function must have a non-null value for all variables. While I can add logic such as if statements to check for null values, why can’t I simply pass through null values and have them be ignored?

My problem revolves around a function which enters a book into my sql database for my app. If I enter all of the book’s information such as author, title, copyright, ISBN, etc. there is no problem as I am not supplying any null values. If however, I were to leave the copyright or ISBN as Null and try to pass these through to the function I get a nullpointerexception. Sometimes I don’t need to record the ISBN or the copyright (this is an example and not the real app) so instead of making multiple functions such as addBook(…) addBookWithNoISBN(…) addBookWithNoCopyright(…) … what is the better way to do this?

I believe I should be sending all of my variables to the function as a string array and perhaps do some processing in the function itself? Is there a better way?

I hope people get what I’m trying to say, thanks a lot!

Answer 1

Java supports something called method overloading, which lets you define multiple methods having the same exact name, but with different numbers/types of parameters: http://download.oracle.com/javase/tutorial/java/javaOO/methods.html

So you would end up coding a separate method for each possible combination. They would then pass in null values where needed, and call the main method that does the core logic:

boolean test(int param1, String param2) {
    return test(param1, param2, null, null);
}
boolean test(int param1, String param2, String param3) {
    return test(param1, param2, param3, null);
}
boolean test(int param1, String param2) {
    // Do your logic here
    if(param1 == 'foo' && param3 == null)
        return false;
    if(param2 == param3)
        return true;
}

With this, it doesn’t matter if you pass in 2, 3, or 4 variables as the same function is ultimately called with ‘null’ values for things you didn’t pass.

Here’s another example, where you have a single method name that can accept all sorts of input types:

boolean AddBook(int isbn)
{
    Book result = FindBookByISBN(isbn);
    return AddBook(result);
}
boolean AddBook(String asin)
{
    Book result = FindBookByAmazonId(asin);
    return AddBook(result);
}
boolean AddBook(String title, String author)
{
    Book result = FindBookByTitleAndAuthor(title, author);
    return AddBook(result);
}
boolean AddBook(Book theBook)
{
    if(theBook == null)
        return false;

    return MyBookCollection.Add(theBook);
}

Hope that helps!