using arrays & methods with Object Oriented Programing Java

Question

I am learning Java, with that being said, my knowledge is still in the crawling phase of learning java. I have read about using objects in arrays which is very powerful. I am trying to edit this simple example class and test class to show who is the fastest driver, and what is the fastest speed. There are two ways I was thinking on how to solve this. One was find the maximum speed, and find what array number (e.g. array[2]).

I have managed to capture the highest speed in a loop, and the array number. putting it into a method, and then calling it is giving confusing me big time. Any help is much appreciated.

error code I am getting
TestBikeWithArray.java:73: error: bad operand types for binary operator '>'
if (bikeRace[i] > bikeRace[0])
^
first type: Bike
second type: Bike
1 error

Tool completed with exit code 1
They are both Bike classes, I don't get it.

public class Bike{

private String driver;
private int gear;
private int cadence;
private int speed;
private int id;

private static int numberOfBikes = 0;

public Bike(String theDriver, int startGear,int startCadence, int startSpeed){
    driver = theDriver;
    gear = startGear;
    cadence = startCadence;
    speed = startSpeed;
    numberOfBikes++;
    id = numberOfBikes;
}

public String getDriver() {return driver;}
public void setDriver(String d) {driver = d;}


public int getGear(){return gear;}
public void setGear(int g){gear = g;}

public int getCadence(){return cadence;}
public void setCadence(int c){cadence = c;}


public int getSpeed(){return speed;}
public void setSpeed(int s) {speed = s;}

public int getID() {return id;}

public static int getNumberOfBikes() {return numberOfBikes;}

// method to print out contents of object
public String toString ()
{
    StringBuffer sb = new StringBuffer();
    sb.append("\nDriver: " + driver);
    sb.append("\nGear: " + gear);
    sb.append("\nCadence: " + cadence);
    sb.append("\nSpeed: " + speed);
    sb.append("\nID: " + id + "\n");

    return (new String(sb));
} // end toString method

} // end class

main test bike

import java.util.Scanner;
import javax.swing.JOptionPane;

class TestBike
{
public static void main(String[] args)
{
    String message ="";

    Bike[] bikeRace = new Bike[10];

    bikeRace[0] = new Bike("Cersei Lannister", 0, 0, 0);
    bikeRace[1] = new Bike("Daenerys Targaryen", 10, 60, 22);
    bikeRace[2] = new Bike("Robb Stark", 21, 50, 15);

    //testing values
    //bikeRace[3] = new Bike("Melisandre", 31,90,155);
    //bikeRace[4] = new Bike("Margaery Tyrell", 2, 3, 100);

    bikeRace[0].setGear(3);

    for(int i=0; i < Bike.getNumberOfBikes(); i++)
    {
        System.out.println(bikeRace[i].toString());

        //testing, must use a proper function call!
        //System.out.println(bikeRace[i].getDriver());
    } // end for loop

    //find max speed & driver findTheFastestDriver

    //testing stuffs get all drivers
    /*for(int i=0; i < Bike.getNumberOfBikes(); i++)
    {
        System.out.println("Driver: " + bikeRace[i].getDriver());
    }

    //testing get all speeds
    for(int i=0; i <Bike.getNumberOfBikes(); i++)
    {
        System.out.println("Speed: " + bikeRace[i].getSpeed());
    } */

    //****************************************************************/
    //finding fastest bike without a method
    //fastest speed is 22
    /*int fastestBike = bikeRace[0].getSpeed();
    int fastestBikeIndex = 0;
    for(int i=0; i<Bike.getNumberOfBikes(); i++)
    {
        if (bikeRace[i].getSpeed() >= fastestBike)
        {
            fastestBike = bikeRace[i].getSpeed();
            fastestBikeIndex = i;
        }//end if
    }//end for
    System.out.println("fastest Bike Speed: " + fastestBike + " " + " Bike index of " + fastestBikeIndex);*/
    //********************************************************************


    int fastestBikeIndex = findTheFastestDriver(bikeRace);
    System.out.println("\nThe fastest driver is " + bikeRace[fastestBikeIndex].getDriver() + " and the speed of " + bikeRace[fastestBikeIndex].getSpeed() + " mph.");


    System.out.println("\nNumber of Bikes: " + Bike.getNumberOfBikes() + "\n");

} //end of main

public static int findTheFastestDriver(Bike[] bikeRace)
{
    int fastestBike = bikeRace[0].getSpeed();
    int fastestBikeIndex = 0;
    for(int i=0; i < Bike.getNumberOfBikes(); i++)
    {
        if (bikeRace[i].getSpeed() >= fastestBike)
        {
            fastestBike = bikeRace[i].getSpeed();
            fastestBikeIndex = i;
        }//end if
    }//end for
    return fastestBikeIndex;
}

} //end of class

code works :) so happy.

Solution

if (bikeRace[i] > bikeRace[0])

change to

if (bikeRace[i].getSpeed() > bikeRace[0].getSpeed())

Reasoning: You cannot numerically compare non-numerical objects.

Comments

[Tim Bender]

In Java, you should implement Comparable and use the compareTo method to establish a natural ordering for sorting/comparing.

[Patashu]

@Tim Bender's idea is good if (and only if) your objects have a natural ordering

[George Putnam]

thank you for the tip. So when calling the method back. int bikeIndex = findTheFastestDriver(bikeRace) System.out.print("The fastest driver " +bikeRace.getDriver[bikeIndex] + " and is going " + bikeRace.getSpeed[bikeIndex] + " mph."); Still the method call is not correct.

[Ted Hopp]

@TimBender - That's certainly one approach, but "should" is the the wrong word. It's not at all clear that Bike objects have a natural ordering. Even if they did, it's not clear that it should be based on speed. Why not on id, or on the lexical order of driver?

[George Putnam]

I never thought of that Tim. I figured since I am looking for the fastest driver, look for the highest speed first. let me take a look again at the code.

[George Putnam]

Thank very much for the explanations. I found the explanations very helpful. I need to practice more on methods, arrays, and objects to understand them more. practice makes perfect.

[George Putnam]

TimBender, wow on compareTo method. I didn't know about this tool, and reading more up on this subject. very cool, and very powerful. makes this a bit more simple. Will play around with this tomorrow.

[Patashu]

@George Putnam Another tool you should look into is Comparator. If a class doesn't have a single natural sort, you can define a Comparator for it and pass it to operations that expect one, such as sorting and making a PriorityQueue