这个课程的参考视频和图片来自。

    主要学到的知识点有：

• Constructors: A special method called when an object of the class is created
• property pattern and encapsulation(封装): hide the implementation details from the user, so when the class is been inherited, only the methods, but not the members. 
• this: simply refers to the current class. 
• Also allow us to call other constructor in one constructor

public class Foo {    private int _x;  // if class members, and not public, start with underscore.    public Foo()     {        this(1);    }    public Foo(int x)    {        _x = x;    }}

 

• Overload: The method with different parameter but same method name. (for example, the constructors. Java will automatic search for the constructors that fits the parameters passed in)

             e.g. Foo foo = new Foo(8); will automatic search for the second constructor "public Foo(int x)".

• Every class should have a constructor. But the body can be empty. 
• Declare variables as private as possible. Can create getter and setter for the variables to control access to private variables.  based on the encapsulation(封装) concept. 
• Initialize all private variables in constructor. (if not, make them final)
• this disambiguates method parameters from private members, but will name the members with _(unless it is public). Below is an example without "_".

public class Foo {    private int x;    public Foo()     {        this(1);    }    public int setX(int x)    {        this.x = x;    }}

• Use get/set methods to control access to private variables.