The Java programming language defines the following kinds of variables:
1. Instance Variables (Non-Static Fields)
2. Class Variables (Static Fields):A class variable is any field declared with the static modifier; this tells the compiler that there is exactly one copy of this variable in existence, regardless of how many times the class has been instantiated.Additionally, the keyword final could be added to indicate that the number of gears will never change.
3. Local Variable

Nested classes 分为两种: static and non-static. Nested classes that are declared static are simply called static nested classes. Non-static nested classes are called inner classes.

原型如下：

class OuterClass {
    ...
    static class StaticNestedClass {
        ...
    }
    class InnerClass {
        ...
  

class declarations includes:

1. Modifiers such as public, private.

2. class name.

3. the name of the class's parent(sperclass), if any. use extends.

4. class body

constructor的声明与method的声明差不多，constuctor的声明使用class的名字，且没有返回值。你不可以写两个一样的构造函数，使用相同数目和类型的arguments。

Parameters（形参）指的是methods声明时候的 list of variables，耳arguments（实参）是当method is invoked

因为要开发Andorid使用到Java，之前一直都是用C，现在有机会学习object-oriented programming。

可以到http://download.oracle.com/javase/tutorial/java/index.html官网上去看文章。

首先学习的是Object-包括fields及methods。记住这一句话：Hiding internal state and requiring all interaction to be performed through an object's methods is known as data encapsulation — a fundamental principle of object-oriented

因为想要开发一个自行车上的测速仪，所以想在手机上做一个软件，像电脑上上的CPU使用记录可以实时将速度绘制出来。

首先登陆http://developer.android.com/android开发的官网，按照里面的步骤下载SDK，然后还要安装，这个需要很长时间，要下载platform还有sample，tools。

下载Eclipse，这个是程序的开发工具，当然你也可以不用下载，直接用sdk里面的tools，但是使用工具会事半功倍，然后再在Eclipse 里安装ADT。

然后就可以来开发程序了，最简单的就