這個課程的參考視訊和圖片來自youtube。

    主要學到的知識點有：

• Define a method:(motivation: write one time, but use it many times)

1. Access: public, private, protected

• public: Any other class can access a public field or method. (Further, other classes can modify public fields unless the field is declared as final.)
• private: Only current class can access. 
• protected: Accessible within all classes in the same package and within subclasses in other packages.

　　  2. Declaration: static, final

• static: methods can be called without declaring an object of the class first.
• final
  : 

　　  3. Return type: void, int, double, char, String, boolean.

• void: the method has no return value.

　　  4. Method name: 

• TODO: Good name rule: 

　　  5. Parameters:

• Variable Scope Rule:  Variable or method parameter only exists inside the method body. 
• When pass the parameters, only pass the value. That is why when we declare a field in a class, will start with "_", to distinguish variables with the local variable here. 
• TODO: Good paramether name rule

　　  6. Method body: 

• in the block { ... }
• TODO: Good block format rule