括号里的（Qiche）是类型强转，o是他用for in遍历car数组里面的元素，getrom就是获取吨数的方法咯

父类

public class Car {
 protected int xuhao;
 protected String name;
 protected int money;
 public Car(int xuhao,String name,int money)
 {
  this.xuhao=xuhao;
  this.name=name;
  this.money=money;
  
 }

 public void leixing() {
  
  System.out.println(xuhao+"\t"+name+"\t"+money+"元/天");
 }
}

货车类

public class Huoche extends Car {
 private int rom;
 public Huoche(int xuhao,String name,int money,int rom)
 {
  super(xuhao,name,money);
  
  this.rom=rom; 
 }
 public void leixing(){
  
  System.out.println(xuhao+"\t"+name+"\t"+money+"元/天"+"\t"+"载货"+rom+"吨");
 }
public int getrom(){
  
  return rom;
 }
}

汽车类

public class Qiche extends Car {
 private int ram;
 public Qiche(int xuhao,String name,int money,int ram)
 {
  super(xuhao,name,money);
 
  this.ram=ram; 
 }
 public void leixing(){
  
  System.out.println(xuhao+"\t"+name+"\t"+money+"元/天"+"\t"+"载人"+ram+"人");
 }
public int getram(){
  
  return ram;
 }

皮卡类
}

public class Pika extends Car {
 private int ram;
 private int rom;
 public Pika(int xuhao,String name,int money,int ram,int rom)
 {
  super(xuhao,name,money);
  this.ram=ram; 
        this.rom=rom;
 }
 public void leixing(){
  
  System.out.println(xuhao+"\t"+name+"\t"+money+"元/天"+"\t"+"载人"+ram+"载货"+rom+"吨");
 }
public int getram(){
  
  return ram;
 }
public int getrom(){
 
 return rom;
}
}

主类

import java.util.Scanner;

public class Main {

 public static void main(String[] args) {
  
  Main kehu = new Main();
  Car[]  xinghao = new Car[6];
  xinghao[0] =new Qiche(1,"奥迪A4",500,4);
  xinghao[1] =new Qiche(2,"马自达6",400,4);
  xinghao[2] =new Pika(3,"皮卡雪6",450,4,2);
  xinghao[3] =new Qiche(4,"金龙",800,20);
  xinghao[4] =new Huoche(5,"松花江",400,4);
  xinghao[5] =new Huoche(6,"依维柯",1000,20);
  System.out.println("欢迎使用答答租车系统");
  System.out.println("您是否要租车:1是"+"\t"+"2否");
      Scanner in =new Scanner(System.in);
      int i = in.nextInt();
      if(i==1)
      {
      System.out.println("您可租车的类型及其价格表");
      System.out.println("序号"+"\t"+"汽车名称"+"\t"+"租金"+"\t"+"容量");
     xinghao[0].leixing();
     xinghao[1].leixing();
     xinghao[2].leixing();
     xinghao[3].leixing();
     xinghao[4].leixing();
     xinghao[5].leixing();
     System.out.println("请选择您要租的汽车数量");
        int j = in.nextInt();
       Car[] f = new Car[j];
      for(int s=0;s<j;s++)
      {
       System.out.println("请输入第"+(s+1)+"辆车的序号：");
       int c=in.nextInt();
       f[s]=xinghao[c-1];
      }
      System.out.println("请输入租车天数：");
      int d=in.nextInt();
      int u=0;
      System.out.println("您的账单有：");
      System.out.println("**********载人车有：");
      for(Car o:f)
      {
       if(o.xuhao==1||o.xuhao==2||o.xuhao==4)
       {
        System.out.print(o.name);
        u+=((Qiche)o).getram();
       
       }else if(o.xuhao==3)
       {
        System.out.print(o.name);
        u+=((Pika)o).getram();
     
       }
      }
      System.out.println("总载客人数"+u+"人"); 
     System.out.println("\n**********载货车有：");
      int h =0;
      for(Car y:f)
      {
       if(y.xuhao==5||y.xuhao==6)
       {
        System.out.print(y.name);
        h+=((Huoche)y).getrom();
       
       }else if(y.xuhao==3)
       {
        System.out.print(y.name);
       h+=((Pika)y).getrom();
       }
     
      }  System.out.println("总载货数"+h+"吨");
      double qian=0;
      for(Car e:f){
      qian+=e.money;
      }
      qian=qian*d;

      System.out.print("\n*****租车总金额："+qian);
 }
  else
      {
     System.out.println("欢迎下次使用");
     
      }
 }

}