Thread: Need help SORTING AN ARRAY

I am a beginner level java programmer. I have three class files:
AddressBook.class
BanffMarathonRunnerDemo.class
BanffMarathonRunner.class

BanffMarathonRunner extends the AddressBook class. And BanffMarathonRunnerDemo creates the array and calls BanffMarathonRunner.

I have made numerous attempts to sort my array by Time in BanffMarathonRunner. But can not seem to figure it out. Can someone show me how this is done?



public class BanffMarathonRunnerDemo {

public static void main(String[] args) {

BanffMarathonRunner[] runners = new BanffMarathonRunner[15];

runners[0] = new BanffMarathonRunner("Elena", "Brandon", 341, 1);
runners[1] = new BanffMarathonRunner("Thomas", "Molson", 273, 2);
runners[2] = new BanffMarathonRunner("Hamilton", "Winn", 278, 5);
runners[3] = new BanffMarathonRunner("Suzie", "Sarandin", 329, 7);

BanffMarathonRunner firstplace = BanffMarathonRunner.getFastestRunner(runners);
printWinner(firstplace);

} // End of main

static void printWinner(BanffMarathonRunner runner) {
System.out.println("Banff Marathon Winner");
System.out.println(runner.getFirstName() + " " + runner.getLastName());
System.out.println(runner.getTime());
}

} // End of class BanffMarathonRunnerDemo





public class BanffMarathonRunner extends AddressBook {
private int time;
private int years;

public BanffMarathonRunner(String firstName, String lastName, int min, int yr) {
super(firstName);
super.setLastName(lastName);
this.time = min;
this.years = yr;}

public int getTime() {return this.time;}
public int getYears() {return this.years;}
public void setTime(int time) {this.time = time;}
public void setYears(int years) {this.years = years;}

public static BanffMarathonRunner getFastestRunner(BanffMarathonRunner[] runners) {
BanffMarathonRunner fastestRunner = runners[0];

// SORT ARRAY HERE BY TIME
return fastestRunner;
}
} // End of BanffMarathonRunner

Sorry about that. I need to search for the lowest integer (time) and the second lowest integer (time) in the array. But I was thinking I could sort them to get it.

Here's the BanffMarathonRunnerDemo with the array

 
public class BanffMarathonRunnerDemo {
 
    public static void main(String[] args) {
 
        BanffMarathonRunner[] runners = new BanffMarathonRunner[15]; 
 
        	runners[0] = new BanffMarathonRunner("Elena", "Brandon", 341, 1); 
        	runners[1] = new BanffMarathonRunner("Thomas", "Molson", 273, 2);
        	runners[2] = new BanffMarathonRunner("Hamilton", "Winn", 278, 5);
        	runners[3] = new BanffMarathonRunner("Suzie", "Sarandin", 329, 7);
 
        	BanffMarathonRunner firstplace = BanffMarathonRunner.getFastestRunner(runners); 
        	printWinner(firstplace); 
 
    } //  End of main
 
static void printWinner(BanffMarathonRunner runner) {
	System.out.println("Banff Marathon Winner");
	System.out.println(runner.getFirstName() + " " + runner.getLastName()); 
    	System.out.println(runner.getTime()); 
    } 
 
} // End of class BanffMarathonRunnerDemo

And here's the BanffMarathonRunner code

 
public class BanffMarathonRunner extends AddressBook {
    private int time; 
    private int years; 
 
public BanffMarathonRunner(String firstName, String lastName, int min, int yr) {
    super(firstName);
    super.setLastName(lastName);
    this.time = min;
    this.years = yr;}
 
public int getTime() {return this.time;}
public int getYears() {return this.years;}
public void setTime(int time) {this.time = time;}
public void setYears(int years) {this.years = years;}
 
public static BanffMarathonRunner getFastestRunner(BanffMarathonRunner[] runners) {
	BanffMarathonRunner fastestRunner = runners[0];
                  //  SORT ARRAY HERE BY TIME
	return fastestRunner;
    	} 
}

I looked at endless examples online but could not figure it out. Here was one of my approaches.

 
 
import java.util.ArrayList; 
import java.util.Collections; 
 
  public ArrayList<JobCandidate> getSortedJobCandidateByAge() {         
    Collections.sort(jobCandidate, JobCandidate.ageComparator);         
    return jobCandidate;     
  }

This, of course is sample code from a web site. And not applicable to my classes. I just could not figure out what was what.

Thank you for your suggestion. I took some time to review and understand the bubble sort class. As a stand alone class it makes sense to me. However, I don't understand how it applies to my two classes.

BanffMarathonRunnerDemo.
Creates the array strings and integers. (firstname, lastname, time, year)

AddressBook
I have a class with objects firstName and lastName

BanffMarathonRunner
extends addressbook to include objects time and year.

I understand what bubble sort does. I don't undestand how to use it in BanffMarathonRunner to reference the array in BanffMarathonRunnerDemo or the objects in AddressBook.

Forgive me if my termonology is off. This is all new to me.

 
public class BanffMarathonRunner extends AddressBook {
    private int time; 
    private int years; 
 
public BanffMarathonRunner(String firstName, String lastName, int min, int yr) {
    super(firstName);
    super.setLastName(lastName);
    this.time = min;
    this.years = yr;}
 
public int getTime() {return this.time;}
public int getYears() {return this.years;}
public void setTime(int time) {this.time = time;}
public void setYears(int years) {this.years = years;}
 
public static BanffMarathonRunner getFastestRunner(BanffMarathonRunner[] runners) {
	BanffMarathonRunner fastestRunner = runners[0];
 
 
        int n = arr.length;
        for (int i = 0; i < n-1; i++)
            for (int j = 0; j < n-i-1; j++)
                if (arr[j] > arr[j+1])
                {
                    // swap temp and arr[i]
                    int temp = arr[j];
                    arr[j] = arr[j+1];
                    arr[j+1] = temp;
                }
 
	return fastestRunner;
    	} 
}

I'm getting closer. Getting a couple errors.

public static BanffMarathonRunner getFastestRunner(BanffMarathonRunner[] runners) {
 
 
	int n = runners.length;
        		for (int i = 0; i < n-1; i++)
            		for (int j = 0; j < n-i-1; j++)
                			if (runners[j].getTime() > runners[j+1].getTime())
                			{
                    			// swap temp and arr[i]
                    			int temp = runners[j];
                    			runners[j]= runners[j+1];
                    			runners[j+1] = temp;
                			}
	BanffMarathonRunner fastestRunner = runners[0];
	return fastestRunner;
    	}

Error: incompatible types: BanffMarathonRunner cannot be converted to int.

int temp = runners[j];

Error: incompatible types: int cannot be converted to BanffMarathonRunner

runners[j+1] = temp;

closer...

No compile errors. I am getting an error when running it.
java exception in thread main java.lang.nullpointerexception.
at BanffMarathonRunner.getFastestRunner(BanffMarathon Runner.java:23)
at BanffMarathonRunnerDemo.main(BanffMarathonRunnerDe mo.java:12)

I looked up the error but it isn't very clear.

--- Update ---

got it. My array was defined too long. Thank you so much.

--- Update ---

How can something be so frustrating and satisfying at the same time! Again....many thanks for your patience.

another way is using standard Java API

import java.util.Arrays;
import java.util.Comparator;
...
Arrays.sort(runners, 
  Comparator.nullsLast( 
  Comparator.comparing(Runner -> Runner.getTime() )
));