29．编写一个Java应用程序，设计一个汽车类Vehicle，包含的属性有车轮个数 wheels和车重weight。小车类Car是Vehicle的子类，其中包含的属性有载人数 loader。卡车类Truck是Car类的子类，其中包含的属性有载重量payload。每个 类都有构造方法和输出相关数据的方法。最后，写一个测试类来测试这些类的功 能。

//Vehicle类
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("轮子"+wheels+"个，"+"自重"+weight+"t");
}

}
// Car类
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("轮子"+getWheels()+"个"+"自重"+getWeight()+"t");
System.out.println("载客人数："+loader+"人");
}
public int getLoader() {
return loader;
}
public void setLoader(int loader) {
this.loader = loader;
}

}
// Truck类
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("轮子"+getWheels()+"个"+"自重"+getWeight()+"t");
System.out.println("载客人数："+getLoader()+"人");
System.out.println("载重："+payload+"t");
}

}
//主类
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();
	

}

}
///运行结果
轮子4个自重1.0t
载客人数：4人
载重：10.0t
轮子4个自重1.0t
载客人数：4人
载重：50.0t
轮子4个自重1.0t
载客人数：2人
载重：50.0t
轮子8个自重3.0t
载客人数：4人
载重：100.0t