20110608 Java 練習小記

package chapter9;
//汽車 class
class Car
{
 int num;
 double gas;

 void show()
 {
  System.out.println("車號是"+num);
  System.out.println("汽油量為"+gas);
 }
}
public class Sample1 {
 public static void main(String[] args) {
  Car car1 = new Car();
  car1.num = 1234;
  car1.gas = 20.5;
  car1.show();
 }
}

package lab2;//chapter 9
class Car
{
 //設定欄位為 private 型態, 不可以任意存取 private int num;
 private double gas;

 //設定一個 public 型態來存取 public void setNumGas(int n, double g)
 {
  //在這邊設定存取的邏輯  if ( g > 0 && g < 1000)
  {
   num = n;
   gas = g;
   System.out.println("改變車號為"+num+"改變油量為"+gas);
  }
  else
  {
   System.out.println(g+"不是合理的汽油量數字");
  }
 }

 public void show()
 {
  System.out.println("車號是"+num);
  System.out.println("汽油量為"+gas);
 }

}
public class Sample2 {
 public static void main(String[] args) {
  Car car1 = new Car();
  //呼叫剛剛設定的 public method 來存取  car1.setNumGas(1234, 20.5);
  car1.show();
 
  System.out.println("測試不合理的汽油量");
  car1.setNumGas(1234, -20);
  car1.show();
 }
}

package chapter9.lab3;
class Car
{
 private int num;
 private double gas;

 //練習 多載 overloading public void setCar(int n)
 {
  num = n;
  System.out.println("改變車號為"+num);
 }

 //可以有同一個方法, 但是引數不一樣, 稱為overloading
 //這邊的引數使用的是 double 用來改變汽油量 public void setCar(double g)
 {
  gas = g;
  System.out.println("改變油量為"+gas);
 }

 //當然也可以同時設定兩個 public void setCar(int n, double g)
 {
  num = n;
  gas = g;
  System.out.println("改變車號為"+num+"\t改變汽油量為"+gas);
 }

 public void show()
 {
  System.out.println("車號為"+num);
  System.out.println("汽油量為"+gas);
 }

}
public class Sample3 {
 public static void main(String[] args) {
  Car car1 = new Car();
  car1.setCar(1234, 20.5);
  car1.show();
 
  System.out.println("只變更車號");
  car1.setCar(2345);
  car1.show();
 
  System.out.println("只變更油量");
  car1.setCar(30.7);
  car1.show();
 }
}

package chapter9.lab4;
class Car
{
 private int num;
 private double gas;

 //使用建構子, 一般用來初始化值
 //產生一個新物件時候, 就會去執行建構子 public Car()
 {
  num =0;
  gas = 0;
  System.out.println("Car 初始化");
 }

 public void show()
 {
  System.out.println("車號是"+num);
  System.out.println("汽油量為"+gas);
 }

}
public class Sample4 {
 public static void main(String[] args) {
  Car car1 = new Car();
  car1.show();
 }
}

package chapter9.lab5;
class Car
{
 private int num;
 private double gas;

 //這個是沒有引數的建構子 public Car()
 {
  num =0;
  gas =0;
  System.out.println("Car 初始化 num and gas");
 }
 //同樣都是建構子,但是引數不同 public Car(int n, double g)
 {
  num = n;
  gas = g;
  System.out.println("初始化車號"+num+"汽油量"+gas+"的Car");
 }

 public void show()
 {
  System.out.println("車號為"+num);
  System.out.println("汽油量為"+gas);
 }


}
public class Sample5 {
 public static void main(String[] args) {
  //建立物件的時候, 沒有輸入任何引數  Car car1 = new Car();
  car1.show();
 
  Car car2 = new Car(1234, 20.5);
  car2.show();
 
  
 }
}

package chapter9.lab6;
class Car
{
 private int num ;
 private double gas;

 public Car()
 {
  num =0;
  gas = 0;
  System.out.println("Car 初始化");
 }

 public Car(int n, double g)
 {
  //呼叫沒有引數的建構元, this(); 一定要寫在建構子第一行  this();
  num = n;
  gas = g;
  System.out.println("改變車號為"+num+"\t改變油量為"+gas);
 }

 public void show()
 {
  System.out.println("車號為"+num);
  System.out.println("汽油量為"+gas);
 }
}
public class Sample6 {
 public static void main(String[] args) {
  Car car1 = new Car();
  car1.show();
  Car car2 = new Car(1234, 20.5);
  car2.show();
 }
}

package chapter9.lab7;//實體變數 instance variable與實體方法 instance method的練習
class Car
{
 private int num;
 private double gas;

 public Car()
 {
  num = 0;
  gas = 0.0;
  System.out.println("生產初始化汽車");
 }

 public void setCar(int n, double g)
 {
  num = n;
  gas = g;
  System.out.println("初始化車號為"+num+"\t初始化油量為"+gas);
 }

 public void show()
 {
  System.out.println("車號為"+num);
  System.out.println("汽油量為"+gas);
 }

}
public class Sample7 {
 public static void main(String[] args) {
  Car car1 = new Car();
  car1.setCar(1234, 20.5);
  car1.show();
 
  Car car2 = new Car();
  car2.setCar(4567, 30.5);
  car2.show();
 }
}

package chapter9.lab8;
class Car
{
 //使用 static 的修飾子標明是類別變數
 //使用 static 的話那就是整個類別用同一個變數 public static int sum = 0;

 private int num;
 private double gas;

 public Car()
 {
  num = 0;
  gas = 0.0;
  //每呼叫一次 Car(), 就累加一次 sum  sum++;
  System.out.println("生產初始化汽車");
 }

 public void setCar(int n, double g)
 {
  num = n;
  gas = g;
  System.out.println("初始化車號為"+num+"\t初始化油量為"+gas);
 }

 public static void showSum()
 {
  System.out.println("目前總共生產"+sum+"汽車");
 }

 public void show()
 {
  System.out.println("車號為"+num);
  System.out.println("油量為"+gas);
 }
}
public class Sample8 {
 public static void main(String[] args) {
  //先顯示目前 sum 的值, 呼叫類別方法  Car.showSum();
 
  Car car1 = new Car();
  car1.setCar(1234, 20.5);
  car1.show();
  Car.showSum();
 
  //因為有呼叫 Car(), 所以 sum會被累加  Car car2 = new Car();
  car2.setCar(2345, 30.5);
  car2.show();
  //顯示目前 sum 的值, 呼叫類別方法  Car.showSum();
 }
}

package chapter9;
class MyPoint
{
 private int x;
 private int y;

 public MyPoint()
 {
  x = 0;
  y = 0;
 }

 public MyPoint(int px, int py)
 {
  if( px >=0 && px <= 100)
  {
   x = px;
  }
  else
  {
   x = 0;
  }
  if ( py >=0 && py <=100)
  {
   y = py;
  }
  else
  {
   y = 0;
  }
  System.out.println("設定初始座標值");
 }

 public void setX(int px)
 {
  if( px >= 0 && px <= 100)
   {
     x = px;
   }
  System.out.println("設定X座標為"+x);
 }

 public void setY(int py)
 {
  if ( py >= 0 && py <= 100)
   {
    y = py;
   }
  System.out.println("設定Y座標為"+y);
 }

 public int getX()
 {
  System.out.println("讀取X座標");
  return x;
 }

 public int getY()
 {
  System.out.println("讀取Y座標");
  return y;
 }


}
public class Homework9_5 {
 public static void main(String[] args) {
  MyPoint m1 = new MyPoint();
  m1.setX(10);
  m1.setY(5);
  int px1 = m1.getX();
  int py1 = m1.getY();
  System.out.println("X座標為"+px1+"\tY座標為"+py1);
 
  MyPoint m2 = new MyPoint(20, 10);
  int px2 = m2.getX();
  int py2 = m2.getY();
  System.out.println("X座標為"+px2+"\tY座標為"+py2);
 }
}