package bzu.aa;
public class Vehicle {
  protected int capacity;
  public Vehicle (){
    capacity=2;
    System.out.println("执行交通工具类的无参构造方法.");
  }
  public Vehicle(int capacity){
    //super();
    this.capacity=capacity;
    System.out.println("执行交通工具类的有参构造方法.");
  }
  public int getCapacity(){
    return capacity;
  }
  public void setCapacity(int capacity){
    this.capacity=capacity; 
  }
  public void print(){
    System.out.println("交通工具的载客量为:"+capacity); 
  }
}
Car类：
package bzu.aa;
public class Car extends Vehicle {
  protected int speed;
  public Car(){
    super();
    speed=0;
    System.out.println("执行汽车类的无参构造方法.");
    }
  public Car(int speed){
    super(6);
    this.speed=speed;  
    System.out.println("执行汽车类的有参构造方法.");
    }
  public int speedUp(int speed){
    this.speed=speed+10;
    return speed;
  }
  public int speedDown(int speed){
    this.speed=speed-10;
    return speed;
  }
  public void print(){
    System.out.println("汽车的载客量为:"+capacity+";汽车的速度为:"+speed);
  }  
}
Bus类：
package bzu.bb;
import bzu.aa.Car;
public final class Bus extends Car{
  public int capacity;
  public Bus(){
    super();
    capacity=20;
    System.out.println("执行公交车类的无参构造方法.");  
  }
  public Bus(int capacity){
    super(40);
    this.capacity=capacity;
    System.out.println("执行公交车类的有参构造方法.");  
  }
  public void print(){
    System.out.println("公交车的的载客量为:"+capacity+";公交车的速度为:"+speed+";汽车类的载客量为:"+getCapacity());
  }  
}
Test类：
package bzu.bb;
import bzu.aa.Car;
public class Test {
  public static void main(String[] args) {
    Car car=new Car();
    car.speedUp(40);
    car.print();
    car.speedDown(30);
    car.print();
    Bus bus=new Bus(20);
    bus.print();
  }
}