這個課程的參考視訊和圖片來自youtube。

    主要學到的知識點有：

• Class: Blueprint for an object. (e.g. dog is a class)
• Object: custom variables contain state an behavior. (e.g. a two-year old husky is an object of a class dog, it's age is 2, and behavior is bark. then it will have methods like "bark()", "eat(food)")

Define an object:

• If want to use the classes defined in Java, like Scanner, Random. Then need to use import method to import the class libraries. ("Ctrl + Shifl + i "will automatic import/unimport the packages can be refered)

import java.util.Random;

• Show javadoc will help you to understand how to use the class or method.
  This is an example of the Random class we just import above. 

// Generator a random number between 0 - 9

Random generator = new Random();
int i = generator.nextInt(10);

• Reverse a string use StringBuilder. 
  

  String forward = "This is a test";
  StringBuilder sb = new
   
   StringBuilder();
  sb.append(forward);
  String reverseString = sb.reverse().toString();
  System.out.println(reverseString);
  
  // System output result will be: 
  // !tset a si sihT

   

• Math.PI will present pi which is 3.14.... in math. ("Tab" is also our friend to see methods that we can use, so press "Tab" after Math.)

double circ = 2 * Math.PI * radius;