Java How to Program Ch3-3

Java How to Program Ch3-3
(1)
一個java檔案只能有一個public class, 在一個檔案定義兩個以上的public class會產生syntax error
(2)
A static method is special because it can be called without first creating an object of the class in
which the method is declared.
Static method 不需要創建Object就可以使用囉! 例如要執行主要工作的method "main", 在定義的時候就要用:
public static void main(String arg[]) { }
(3)
class instance creation expression 就是 new, e.x. Random r = new Random();
(4)
Random r = new Random();
以這個例子來說, Random後面的"( )"叫做constructor(建構子), 用在Object剛創造出來時, 去初始化該Object的變數(如果此class需要初始化變數的話...像這個例子就沒有初始化任何參數)
(5)
在java檔案被compile且execute的時候, main這個method會被自動執行, 不需要programmer去寫程式call它
(6)
By convention, method names begin with a lowercase first letter and all subsequent words in the name begin with a capital letter.
ex. methodNumberOne
(7)
javac *.java -> 將該folder下所有的.java檔進行compile!!
javac Alice.java Bob.java Candy.java ->complie這三個java檔案
(8)
What is UML
UML is a graphical language used by programmers to represent object-oriented systems in a standardized manner. 在思考一個龐大程式架構時十分有用
in UML, + displayMessage( ) ->+號的意思是該method是public!