29．編寫一個Java應用程序，設計一個汽車類Vehicle，包含的屬性有車輪個數 wheels和車重weight。小車類Car是Vehicle的子類，其中包含的屬性有載人數 loader。卡車類Truck是Car類的子類，其中包含的屬性有載重量payload。每個 類都有構造方法和輸出相關數據的方法。最后，寫一個測試類來測試這些類的功 能。

//Vehicle類
package d922A;

public class Vehicle {
private int wheels;
private double weight;
Vehicle()
{
weight=1;wheels=4;
}
Vehicle(int lun, double zizhong)
{
wheels=lun;
weight=zizhong;
}
public int getWheels() {
return wheels;
}
public void setWheels(int wheels) {
this.wheels = wheels;
}
public double getWeight() {
return weight;
}
public void setWeight(double weight) {
this.weight = weight;
}
public void showData(){
System.out.println("輪子"+wheels+"個，"+"自重"+weight+"t");
}

}
// Car類
package d922A;

public class Car extends Vehicle {
private int loader;
Car()
{
loader=4;
}
Car(int zaikeshu)
{
loader=zaikeshu;
}
Car(int lun, double zizhong,int zaikeshu)
{
super(lun,zizhong);
loader=zaikeshu;
}
public void showData(){
System.out.println("輪子"+getWheels()+"個"+"自重"+getWeight()+"t");
System.out.println("載客人數："+loader+"人");
}
public int getLoader() {
return loader;
}
public void setLoader(int loader) {
this.loader = loader;
}

}
// Truck類
package d922A;

public class Truck extends Car {
private double payload;
Truck()
{
payload=10;
}
Truck(double zaizhong)
{
payload=zaizhong;
}
Truck(int zaikeshu,double zaizhong)
{
super(zaikeshu);
payload=zaizhong;
}
Truck(int lun, double zizhong,int zaikeshu,double zaizhong)
{
super(lun,zizhong,zaikeshu);
payload=zaizhong;
}
public void showData(){
System.out.println("輪子"+getWheels()+"個"+"自重"+getWeight()+"t");
System.out.println("載客人數："+getLoader()+"人");
System.out.println("載重："+payload+"t");
}

}
//主類
package d922A;

public class Testvec {

public static void main(String[] args) {
	Truck a=new Truck();
	a.showData();
	a=new Truck(50);
	a.showData();
	a=new Truck(2,50);
	a.showData();
	a=new Truck(8,3,4,100);
	a.showData();
	

}

}
///運行結果
輪子4個自重1.0t
載客人數：4人
載重：10.0t
輪子4個自重1.0t
載客人數：4人
載重：50.0t
輪子4個自重1.0t
載客人數：2人
載重：50.0t
輪子8個自重3.0t
載客人數：4人
載重：100.0t