How to sort array objects into alphabetical order...

(Updated: see latest post!)

Hi,

I have written a small program which is supposed to read in records of student marks stored in a text file. It is then supposed to print out the records, ordered alphabetically by surname.

I have done most of it... see here:
gillinghamband.org/java/Results.java

but am struggling to work out how I can sort the objects in the array into alphabetical order by comparing the surname variable of each array object...

...so if anyone has any hints about how I can do that, it would be greatly appreciated! :-)

...also it would be good to get some general feedback about how my code could be improved... (I do feel like I've written a lot of code in order to achieve something that sounds like it should be fairly simple...!)

Thanks,

Lisa :)

The easiest way to sort is to make sure your Student class (or whatever class you have that stores the Student's name together with his/her test scores) implements the Comparable<Student> interface. If you do this, then if your array is called students, simply use the Arrays.sort(students) method to sort the array. Your compareTo method will need to compare the surnames. The easiest way for it to do this is to simply use String's compareTo method.

Thanks for the reply. I'm still having some problems getting my code to work :-(

Basically, everything is ok up until where I have added in the recordSort method - Here, the compiler complains lots about the fact that it can't see my RecordArray variable from within the method.
I have tried placing the method in different places but with no luck so far... I am a bit stuck as to how I should restructure my code to make it compile...

Also I am not entirely sure if I have written my compareTo method correctly...

Any advice would be very much appreciated! (I will post my code below)

Thanks :-)

import java.io.File;
import java.io.FileReader;
import java.io.BufferedReader;
import java.io.IOException;
import java.lang.NumberFormatException;
import java.util.StringTokenizer;
import java.util.Arrays;


public class Results {

Record[] RecordArray;

static public class Record {
char[] RecordInitials;
String RecordSurname;
int RecordMark;

//method to set initials for record
public void setInitials(char[] InitialsArray) {
RecordInitials = InitialsArray;
}

//method to get initials for record
public char[] getInitials() {
return RecordInitials;
}

//method to set surname for record
public void setSurname(String SurnameString) {
RecordSurname = SurnameString;
}

//method to get surname for record
public String getSurname() {
return RecordSurname;
}

//method to set mark for record
public void setMark(int MarkInt) {
RecordMark = MarkInt;
}

//method to get mark for record
public int getMark() {
return RecordMark;
}

} //end of record class


public static void main(String[] args) {

//check that an arg has been supplied
if (args.length == 0) {
System.out.println ("no filename specified");
System.exit(1);
}

BufferedReader textFileBuffer = null;

try {
File textFile = new File(args[0] + ".txt");
FileReader textFileReader = new FileReader(textFile);
textFileBuffer = new BufferedReader(textFileReader);


String line;
int z = 0;
Record[] RecordArray = new Record[100];


while ((line = textFileBuffer.readLine()) != null) { //while there are still lines to read...
//reset the 3 variables ready for new values of the next record
char[] initials = new char[5];
String surname = " ";
int mark = 0;

StringTokenizer token = new StringTokenizer(line);
int x = 0;
int y = 0;

while (token.hasMoreTokens()) { //while there are more tokens on the line...

String aSingleToken = token.nextToken(); //extract the next token

//if token is a number it goes into the marks variable
boolean isNumber = false;
try {
mark = Integer.parseInt(aSingleToken);
isNumber = true;
}
catch(NumberFormatException nfe) {
isNumber = false;
}
//if token is a length 1 and not a number it goes into the initials char array
if (aSingleToken.length() == 1 && !(isNumber)) {
initials[y] = aSingleToken.charAt(0);
y++;
}

//if token is > 1 and is not a number it goes into String surname variable
if(aSingleToken.length() > 1 && !(isNumber)) {
surname = aSingleToken;
}

x++;
} //end of while there are more tokens on the line...

//the 3 variables above then get put into a Record object and object gets put into an array of record objects



RecordArray[z] = new Record();
RecordArray[z].setInitials(initials);
RecordArray[z].setSurname(surname);
RecordArray[z].setMark(mark);


z++;
} //end of while there are more lines to read



System.exit(0);


}
catch(IOException ioe) {
System.out.println("Error opening file " +args[0] + ".txt");
System.exit(1);
}





} //end of main method


//sort array objects into alphabetical order by surname
//by comparing surname part of each object
public void RecordSort() {
int i, j;
Record temporary;
for (i = 0; i < RecordArray.length - 1; i++) {
for (j = RecordArray.length-1 ; j >i; j--) {
if ((RecordArray[j].getSurname().compareToIgnoreCase( RecordArray[j -1].getSurname()) ) < 0 ) {
temporary = RecordArray[j];
RecordArray[j] = RecordArray[j -1];
RecordArray[j-1] = temporary;
}
}
}

}




//method to print out records
public void PrintRecord() {
for (int i = 0; i < RecordArray.length - 1; i++) {
System.out.print(RecordArray[i].getInitials());
System.out.print(RecordArray[i].getSurname());
System.out.println(RecordArray[i].getMark());
}
}


} //end of Students class

Argh, actually, scrap that! I have solved my first issue by putting "Record[] RecordArray; right at the top of my code, just below the Results class!
That's got rid of about 12 error messages all at once! :-)

The only thing I think I need to sort out now is how to correctly write my compareTo method...

Update: I have worked out why my comareTo method wasn't working and have corrected that...

...I still have one more issue though - I don't know how to call my RecordSort() or my PrintRecord() methods so that the records actually get sorted and printed...

I have updated my code above to the latest version...any suggestions would be greatly appreciated :-)