如何搜索数组并检查 Java 中的条件

Question

I have an array of both new cars and used cars. I want to search through the array for the cars who have the color green. The method printAllCarsOfColor(String color) will return a string which displays the information of all cars of a color given as argument. I have tried but no luck.

I have Car class which is the superclass and NewCar and UsedCar that are subclasses. Only NewCar class has the Color method. I can't figure out how to print out the cars that are only green.I understand that the method Color is not defined for Car class.

Looking for some help. Thanks!

My code:

public class CarDearlerShip
{
   private Car[] aCar;
   private int count;
   private int car;
  
   public CarDearlerShip()
   {
     aCar = new Car[80];
      count = 0;
      car = 0;  
   }
  
   
   public void addNewCar(String model, int year, int price, String color)
   {
      aCar[count] = new NewCar(model, year, price, color);
      count++;
   }   
   
   public void addUsedCar(String model, int year, int price, boolean rusty)
   {
      aCar[count] = new UsedCar(model, year, price, rusty);
      count++;
   } 
   
   public String printReport()
   {
      String report = "---------------------------------------------\n";
      report += "The list of availabel cars:\n\n";
      
     for (int car = 0; car < count; car++)
      report += aCar[car].toString() + "\n";
      //System.out.println(report);
    return report;
      
   }
   
  public String printAllCarsWithSellingPriceBelow(int price) 
   {
      String printCars = "---------------------------------------------\n";
      printCars += "The price for these cars are: \n\n";
      
      for (int car = 0; car < count; car++)
      {
          if (aCar[car].aPrice < 1000); // The argument for the selling price
          printCars +=aCar[car].getPrice();
      }
         return printCars;       
   
   }
   
   public String printAllCarsOfColor(String color)
   {
      String printColor = "---------------------------------------------\n";
      printColor += "The color : \n\n";
      
      
      for (int car = 0; car < count; car++)
      {
         if (aCar[car].Color()==color);
         printColor +=aCar[car];
         
      }
      return printColor;      
   
   }
}

The Test Class
    
public class TestDealer 
{
    public static void main(String[] args)
    {
        CarDearlerShip dealer= new CarDearlerShip();
        dealer.addNewCar("GM Buick Century", 2004, 200000, "Silver");
        dealer.addUsedCar("Toyota Corolla", 1999, 9000, true);
        dealer.addNewCar("Honda Civic", 2004, 500, "Green");
        dealer.addNewCar("BMW 320i", 2004, 35000, "Black");
        dealer.addUsedCar("Toyota Sienna", 2000, 11000, false);
        
            System.out.println(dealer.printReport());
            System.out.println("**********************************");
        
        //System.out.println(dealer.printAllCarsWithSellingPriceBelow(1000));
            
            System.out.println("****************************************");

        System.out.println(dealer.printAllCarsOfColor("Green"));
        
        
    }

}

Answer 1

When you are comparing the output of the Color method that your car has you need to be using the built in java.lang.String method.equals().

In your code you have: if(aCar[car].Color()==color){

But it needs to be if(aCar[car].Color().equals(color)){

Basically the compiler is never going to understand what you are saying because the String variable "Color" is just a pointer to a space in your computer's memory where it is storing the value "green." So when you compare "green" to that pointer they will never be the same.