Java help

[xtothez]

Here's one for you java users:

Using the Student class provided write a program to create and array of students populated with data (minimum of 5). Print this array, then sort it on lastName and print the sorted array

Student.java
public class Student
{
   private String firstName, lastName, id;

   //-----------------------------------------------------------------
   //  Sets up this Student object with the specified initial values.
   //-----------------------------------------------------------------
   public Student (String first, String last, String number)
   {
      firstName = first;
      lastName = last;
      id = number;
   }

   //  Returns this Student object as a string.
   public String toString()
   {
      String result;

      result = firstName + " " + lastName + " " + id + "\n";

      return result;
   }
}

import avi.*;

class ex1 {

	public static void main(String[] args) {
		Window screen = new Window("ex1,java");
		Student[] list = new Student[5];
		
		list[0] = new Student("Bob","Thomas","1");
		list[1] = new Student("Tim","Armstrong","2");
		list[2] = new Student("Liz","Hope","3");
		list[3] = new Student("John","Smith","4");
		list[4] = new Student("Billy","Nomates","5");
		
		screen.showWindow();
		
		for (int index=0; index != list.length; index++) {
			screen.write(list[index].toString()+"\n");
				
		}
						
	}
}

As you can see, I can fill the array no problem and print it in order. But I have no idea to sort it on lastName. The Student class returns a String with the firstName, lastName and id all concatenated, and I see no way to read the first char of lastName.
Any help would be much appreciated.

[pablissimo]

You could write a custom sorting routine that looks at each LastName in turn and puts them into a temporary array called Sorted or something, then copy the sorted array back...

You covered sorting algorithms yet?

[Nodrog]

add a getLastName() method to your student class which returns the last name. Parsing the toString() data to get it would be insanely bad OO design.

[Atamur]

are you permitted to use Collection framework or are you supposed to write your own sorting routine?

class LastNameCmp implements Comparator {
public int compare(Object o1, Object o2) {
return ((Student) o1).getLastName().compareTo(((Student) o2).getLastName());
}
}

....

Arrays.sort(list, new LastNameCmp());

or, if you are allowed to modify Student class, you can make it implement Comparable and define compareTo method instead of defining a separate comparator class.

[xtothez]

For those interested in the solution, I found a new way to do it:

import java.lang.*;
public class Student implements Comparable
{
   private String firstName, lastName, id;

   //-----------------------------------------------------------------
   //  Sets up this Student object with the specified initial values.
   //-----------------------------------------------------------------
   public Student (String first, String last, String number)
   {
      firstName = first;
      lastName = last;
      id = number;
   }
	
   //  Returns this Student object as a string.
   public String toString()
   {
   	  String result;
      result = firstName + " " + lastName + " " + id + "\n";
      return result;
   }
   
   public int compareTo(Object object) {
   		
   		return (((Student)this).lastName).compareTo(((Student)object).lastName);
   }
}

import avi.*;
import java.util.*;

class ex1 {

	public static void main(String[] args) {
		Window screen = new Window("ex1.java");
		Student[] list = new Student[5];
		int index;
		
		list[0] = new Student("Bob","Thomas","1");
		list[1] = new Student("Tim","Armstrong","2");
		list[2] = new Student("Liz","Hope","3");
		list[3] = new Student("John","Smith","4");
		list[4] = new Student("Billy","Nomates","5");
		
		screen.showWindow();
		screen.write("Array before sorting:\n\n");
		
		for (index=0; index != list.length; index++) {
			screen.write(list[index].toString());
		}
		Arrays.sort(list);
		screen.write("\n\nArray after sorting:\n\n");
		for (index=0; index != list.length; index++) {
			screen.write(list[index].toString());
		}
	}
}

[xtothez]

Originally posted by Atamur

Oops, just noticed your post there now. I ended up doing it that way, it would have been done a bit sooner if I was more awake though...

thx