Android
- Sample code
- Common Android tasks
- Code snippets
- apps-for-android project – open source apps
- Android drawables
- stackoverflow for Android
Book reference: This is your best reference book on Java: Head First Java, 2nd Edition Amazon O'Reilly. You can read most of this on Google Books. The missing pages are right here.
Q: What are Java classes?
In Java you have objects, and every object has a template that defines what its properties and functions are. A Cat can cat.eat() (a method) and a cat has a cat.furColor (a property). When you make a new Cat you give it the properties and functions on its class.
In Android, classes are used for a lot of things. MainActivity is a class, as well as SQLiteOpenHelper. They don't have a lot in common other than that they have a file named MainActivity.java and SQLiteOpenHelper.java and a bunch of properties and functions inside them. Read the documentation carefully for what a class should have.
Q: What is this in Java?
When you call a function like kitty.eat("humans"), kitty is an object of the class Cat. So in your Cat.java file, you'll have a method (aka a function) called public void eat(String something) { ... } or something to that effect. Inside of this function, if you talk about the magic this variable, it's referring to the kitty you called the eat() method on.
(Sidenote: a "method" is a function defined in a class and thus all methods already have a "this" object.)
Android documentation on SQLite: [http://developer.android.com/guide/topics/data/data-storage.html#db)(http://developer.android.com/guide/topics/data/data-storage.html#db)
SQL is a way of interacting with a database. If you imagine your filesystem lets you open, close, delete, rename, and move files, SQL is a way of telling a database to do those types of interactions with your data.
SQL fundamentally is a gross looking string that describes an action you want to do:
SELECT * FROM my_notes WHERE done = 0This selects from the table my_notes all data fields (the * used there) where the done field is 0 (thus, all incomplete notes)
Because this is the ugliest way to work with data, we usually wrap this up in nice big Java classes.
Q: How do I use my database using nice, big Java classes? (How do I use SQLite on Android?)
Glad you asked. This tutorial on AndroidHive presents a nice way to model a row in your database (here Contact) and a way to create, delete, and find contacts (here DatabaseHelper).