{column}
{column}{column}
{section}
If you understand this code, particularly how the keywords {{this}} and {{static}} work, and you can predict the output as shown below,
{toggle-cloak:id=Cat Code Output} _Cat Code Output_ 
{cloak:id=Cat Code Output|visible=false} 
{noformat}
Hello World!  My name is Mr. Mistoffelees and I am 8 years old. I am magical.
Hello World!  My name is Garfield and I am 12 years old. I am tired/hungry.
Mr. Mistoffelees and Garfield are friends? false
Mr. Mistoffelees and Garfield are friends? true
{noformat}
{cloak}
then you probably don't need to expand the section below and can continue. 
{toggle-cloak:id=Cat Code Explained} _Cat Code Explained_ 
{cloak:id=Cat Code Explained|visible=false} 
First, lets talk about the contents of the files {{Cat.java}}.
* _Fields_: The class {{Cat}} has three fields, {{name}}, {{age}} and {{friend}}.  Each field has a _type_, which ensures that we can only store a {{String}} in {{name}}, an {{int}} in {{age}} and another {{Cat}} in {{friend}}.  The word {{private}} before each field indicates that the field can only be accessed from within the class {{Cat}}.
* _Constructors_: The class {{Cat}} has one constructor {{public Cat(String name, int age){...\}}}.  In the constructor, the fields {{name}} and {{age}} are initialized with the values given in the arguments, while {{friend}} is simply set to {{null}}.  Because the constructor is public, it can be invoked from other classes.  An example of the  invoking the constructor can be seen in {{CatsTheMusical.java}}.
* _Methods_: The class {{Cat}} has four methods, {{getName(){...\}}}, {{getFriend(){...\}}}, {{setFriend(Cat friend){...\}}} and {{sayHello(String aboutMe){...\}}}.  The keyword {{public}} indicates that the methods can be called outside of the class {{Cat}}.  The second word in each method is the _return type_, or the _type_ of the result of the method.  Notice that {{setFriend(...)}} has a return type of {{void}}, indicating that nothing is returned.  The first two methods are examples of _getter_ methods, as they simply retrieve the value of a private field.  The third method is a _setter_ method, which allows the field {{friend}} to be changed from outside the class {{Cat}}.

Now lets talk about the other file {{CatsTheMusical.java}}.
* _Static Methods_: Methods that are {{static}}, while associated with the class they are written in, are not associated with any particular instance.  They can be invoked by using {{\[class-name\].\[method\]}}.  For example, see the invocation of {{areFriends(...)}} within {{main(...)}}.
* _main(...)_: All Java program must start with the code {{public static void main(String[] args){...\}}}.  From here, we will follow the methods and constructors into other class files.  The arguments, {{String\[\] args}} can be accessed by calling {{args\[0\]}} etc. and can be set by going to the top menu bar and then selecting _Run → Run Configurations..._, then selecting the _Arguments_ tab in the center and filling out the _Program Arguments_ box.

Now that we have the basic terminology down, lets examine some of the finer points which may be confusing to non-Java programmers:
* Given an instance of a class (e.g. for {{Cat c = new Cat(...)}}, {{c}} is an instance), non-static methods from the class can be called by \[instance name\].\[method name\] (e.g. {{c.getName()}}).  Similarly, non-static fields can be accessed by calling \[instance name\].\[field name\], (e.g. {{c.name}}).  However, methods or fields labeled {{private}} can only be called/accessed from code written within their own class file.
* Within a constructor, we can directly access the fields of a class by name without reference to any particular instance, as it is implied that the instance is the one that is being built.  For example, in the {{Cat}} constructor, we make the assignment {{friend = null}}.  However, when there are argument variables with the same name as the field variables, they take precedence and _shadow_ the fields variables.  To reference the fields once they have been shadowed, you need to use the keyword {{this}}.  In fact, you can use the keyword {{this}} whenever you want to refer to a field or method of the instance of the class being built by the constructor, regardless of whether there is shadowing.  The same rules when you are inside a non-static method instead of inside a constructor.
* In static methods, we cannot refer to any non-static fields or non static methods of the class without also providing an instance, as static methods are not associated with any instance.  Similarly, the keyword {{this}} cannot be applied.

{cloak}

Now you are ready for some more advanced Java!

h1. Types, Primitives, and Generics

TODO... but until then

* Try [here|http://docs.oracle.com/javase/tutorial/java/generics/] for generics, up to Generics, Inheritance, and Subtypes.
* Autoboxing [http://docs.oracle.com/javase/tutorial/java/data/autoboxing.html

]


h1. Inheritance, Abstract Classes, Interfaces, and Inner Classes

TODO... but for now

* Things in here are all pretty important [http://docs.oracle.com/javase/tutorial/java/IandI/index.html

]


h1. Data Structures

TODO... but for now

* The Java Collections documentation [http://docs.oracle.com/javase/tutorial/collections/index.html

]
** Interfaces: Sets, Lists, and Maps

** Implementations: HashSet, ArrayList, HashMap

* [Guava|http://code.google.com/p/guava-libraries/wiki/GuavaExplained?tm=6]
** [BiMap|http://code.google.com/p/guava-libraries/wiki/NewCollectionTypesExplained#BiMap]
** [Immutable Collections|http://code.google.com/p/guava-libraries/wiki/ImmutableCollectionsExplained]