JAVA 範例 ch09 Sample8

使用類別變數、類別方法

/*使用類別變數、類別方法*/
//車子類別
class Car
{
 public static int sum=0;   //這是類別變數

 private int num;
 private double gas;
 
 public Car()
 {
  num=0;
  gas=0.0;
  sum++;   //建構式每一次被呼叫，都會使類別變數sum的值遞增1
  System.out.println("生產了車子。");
 }
 public void setCar(int n,double g)
 {
  num=n;
  gas=g;
  System.out.println("將車號設為" + num + "，將汽油量設為" + gas + "。");
  //this.show();
 }
 public static void showSum()   //這是類別方法
 {
  System.out.println("車子總共有" + sum + "台。\n");
 }
 public void show()
 {  
  System.out.println("車號是" + num + "。");
  System.out.println("汽油量是" + gas + "。");
 }
}

class Sample8
{
 public static void main(String[] args)
 {
  Car.showSum();   //呼叫類別方法
      
  Car car1=new Car();   //建立新物件 
  car1.setCar(1234,20.5);
    
  Car.showSum();   //再次呼叫類別方法
  
  Car car2=new Car();
  car2.setCar(4567,30.5);
  
  Car.showSum();
 }
}