Passing Objects into Methods

[Maureen Charlton]

I have the following code:

 
   //Method to convert the vehicleObject to something more meaningful
   //i.e. at the moment it displays the address vehicle@6789930
   public String convert (Vehicle vehicleObject)
   {
        String convertedObject;
        Vehicle vehicleTypes = vehicleObject;
        for (int i = 0; i < numberOfVehicles; i++)
        {
            convertedObject = toString( ).vehicleTypes[i];
            return convertedObject;
        }//end for loop
   }//end method convert
 

I get the following error:
C:\java>javac Vehicle.java
Storage.java:69: cannot resolve symbol
symbol : variable vehicleTypes
location: class java.lang.String
convertedObject = toString( ).vehicleTypes[i];

Could someone explain why it can not resolve the symbol vehicleTypes.

(Thanking you in advance).

[Paul Sturrock]

What the compiler is telling you is it is looking for a variable called vehicleTypes in the String class. Why is it looking for this variable in the String class? Its the line:

convertedObject = toString( ).vehicleTypes[ i ];

What you are asking here is for an object of whatever class this method is in to call toString() (which returns a String), then access the variable vehicleTypes. Of course when toString() is finished, you are dealling with a String, not whatever object has a public static array called vehicleTypes.
[ November 11, 2004: Message edited by: Paul Sturrock ]

[Junilu Lacar]

Maureen,

From what you have posted so far, I can only glean the following:
1. You have a Vehicle class
2. You have been trying to System.out.println(Vehicle) but don't
want the result to be the default (the result of toString()).

So, here's what I think you are trying to do:

/*
 * Vehicle.java
 */
 
public class Vehicle {
   private String type;
 
   public Vehicle(String newType) {
       type = newType;
   }
 
   public String getType() {
       return type;
   }
}
 
/*
 *  Test.java
 */
public class Test {
    public static void main(String[] args) {
         Vehicle[] smallCars = 
             { new Vehicle("Toyota Corolla"),
               new Vehicle("Honda Civic"),
               new Vehicle("Ford Focus"),
               new Vehicle("Chevy Malibu"),
               new Vehicle("Mitsubishi Eclipse") };
  
         for (int i = 0; i < smallCars.length; i++) {
              System.out.println(smallCars[i].getType());
         }
    }
}

Alternatively, you could override Vehicle.toString():

/*
 * Vehicle.java
 */
 
public class Vehicle {
   private String type;
 
   public Vehicle(String newType) {
       type = newType;
   }
 
   /** 
    * Overrides inherited toString()
    */
   public String toString() {
       return type;
   }
}
 
/*
 *  Test.java
 */
public class Test {
    public static void main(String[] args) {
         Vehicle[] smallCars = 
             { new Vehicle("Toyota Corolla"),
               new Vehicle("Honda Civic"),
               new Vehicle("Ford Focus"),
               new Vehicle("Chevy Malibu"),
               new Vehicle("Mitsubishi Eclipse") };
  
         for (int i = 0; i < smallCars.length; i++) {
              // println() calls the toString() method
              // of Objects passed to it.
              System.out.println(smallCars[i]);
         }
    }
}

HTH

[Maureen Charlton]

Junilu Lacar,

Many thanks with your response. Much appreciated.

Following what you said above I decided to create a class that I can use over and over again. I called it Override. This class is used when I try to System.out.println (.............. what ever), when I don't want the result to be the default (the result of toString ( ) ). As you mentioned.

So my class is like this:

 
/*File name:  Override.java
   Written by Maureen Charlton  ref: 52/1677
 
   Requirements:
   A class to over ride the toString( )
 
*/
 

import java.util.*;
 
public class Override
{
    //Member section
        //Private members
        private String type;
 

        //Public members
 

    //Constructor section
 
    public Override (String newType)
    {
        type = newType;
    }
 
    //Method section
 
    //Overrides inherited to String ( )
    public String toString ( )
    {
        return type;
    }//end method toString
 
    public static void main(String [ ]args) 
    {
 
        System.out.println ("\nOver ride executed and finished");
 
    }//end main program
}//end public class Override
              

This class compiles and executes as expected but when I try to use it, it is a different matter.

public void storeStudent (Student studentObject [ ])
{
for (lp = 0; lp<numberOfStudents; lp++)
{
System.out.println ("\nstudentObject Before override: "+studentObject[lp] );
//Over ride toString
Override(studentObject[lp]);
System.out.println ("\nstudentObject After override: "+studentObject[lp] );

The offending code is when I call the Override class and pass the studentObject[lp] into it.

My first thoughts were in my Override class I declared a variable of 'type' String when it should perhaps be Student - however this was unsuccessfull.

Could you point me in the right direction to correct this? Or alternatively suggest what I am doing wrong?

Thanking you in advance!

[Paul Sturrock]

What you've done is a little confused Maureen. Have another look at the second Vehicle class Junilu Lacar posted. What that does is provide a toString method specific to the Vehicle class, which overriders the one it inherits from the Object class (which all Java Objects implicitly extend). You don't need a seperate class to override the toString() method, just override the method in your Vehicle class.

Where you do this:

Override(studentObject[lp]);

I'm suprised you say it compiles - it shouldn't unless you have a method called "Override" in the same class you have this line. I think you have may confused how you call a method on another object. There's two ways:

By creating an instance of a new object and calling a method on that instance e.g.

Override obj = new Override(studentObject[lp]);
obj.toString(); 

Or by calling a static method, like this:

Override.toString(studentObject[lp]);

As I've said though, if all "Override" is there to do is override the toString method of another object, then its unneccessary. You just need to add the toString() method to your Vehicle class.

Any questions - don't hesitate to ask.
[ November 15, 2004: Message edited by: Paul Sturrock ]