Help with Java project!!!

Question

Please help me out with this, I've written this as a start to my program about kids grades and it won't compile!! I've tried everything, I just have no clue why it won't work.
// John: firsts.java
import javax.swing.*;
public class firsts {
public static void main ( String args[] )
{ int Students;
int firsts;int twoone; int twotwo; int third; int pass; int fail; int resultCounter; int result;
int total;
double average;
String StudentsString;
//initialisation
firsts = 0;
twotwo = 0;
twoone = 0;
third = 0;
pass = 0;
fail = 0;
resultCounter = 0;
total = 0;
Students = 0;
StudentsString = JOptionPane.showInputDialog ( "Enter number of students in the class (up to 20): " ) ;
Students = Integer.parseInt( StudentsString);
if ( Students <=-1 || >=21 ) JOptionPane.showMessageDialog ("No such Account Number", JOptionPane.ERROR_MESSAGE);
else if ( Students == 0 ) System.exit(0) ;
else JOptionPane.showMessageDialog("Class average is ", JOptionPane.INFORMATION_MESSAGE );
ERROR REPORT:-
C:\WINDOWS\Desktop\Johns Java>C:\j2sdk1.4.1\bin\javac firsts.java
firsts.java:36: illegal start of expression
if ( Students <=-1 || >=21 ) JOptionPane.showMessageDialog ("No such Account Number", JOptionPane.ERROR_MESSAGE);
^
firsts.java:36: ')' expected
if ( Students <=-1 || >=21 ) JOptionPane.showMessageDialog ("No such Account Number", JOptionPane.ERROR_MESSAGE);
^
firsts.java:42: cannot resolve symbol
symbol : method showMessageDialog (java.lang.String,int)
location: class javax.swing.JOptionPane
else JOptionPane.showMessageDialog("Class average is ", JOptionPane.INFORMATION_MESSAGE );
^
3 errors
What am I doing wrong? Please help!!!

Answer 1

Again, I've been all around the bushes trying to alter this but I still get 13 errors! Everytime a mark is entered I am trying to add it into the correct category so that at the end I can see how many have firsts, seconds, thirds etc. I just cannot see what I'm doing wrong.
// John: arp.java
import java.awt.event.*;
import javax.swing.*;
public class arp extends JFrame {  public arp() 
{    double average;   
String StudentsString;
// declaration and initialisation //
int firsts = 0;
int twotwo = 0;
int twoone = 0;
int third = 0;
int pass = 0;
int fail = 0;
int resultCounter = 0;
int total = 0;
int Students = 0;
int Studentmark;
StudentsString = JOptionPane.showInputDialog(this,"Enter number of students in the class (up to 20): ");
{      Students = Integer.parseInt(StudentsString);    }
// could also write this as //
if(Students <= -1 || Students >= 21)
JOptionPane.showMessageDialog(null, "ERROR", "The number needs to be between 0-20", JOptionPane.ERROR_MESSAGE);
else if(Students == 0)
System.exit(0);
else while (resultCounter <= Students) resultCounter ++;
JOptionPane.showInputDialog(this,"Enter mark (0-100) for Student" + resultCounter + " :- ");
{ Studentmark = Integer.parseInt(StudentsString);}
if (Studentmark >=70 && <=100) firsts++;
else if (Studentmark >=60 && <=69) twoone++;
else if (Studentmark >=50 && <=59) twotwo++;
else if (Studentmark >=41 && <=49) third++;
else if (Studentmark >=38 && <=40) pass++;
else if (Studentmark >=37 && <=0) fail++;
else JOptionPane.showMessageDialog(null, "ERROR", "The student mark needs to be between 0-100", JOptionPane.ERROR_MESSAGE);
addWindowListener(new WindowAdapter() {     public void windowClosing(WindowEvent e) {       System.exit(0);     } }); //
arp.java:44: illegal start of expression
if (Studentmark >=70 && <=100) (firsts++);
^
arp.java:44: ')' expected
if (Studentmark >=70 && <=100) (firsts++);
^
arp.java:46: illegal start of expression
else if (Studentmark >=60 && <=69) (twoone++);
^
arp.java:46: ')' expected
else if (Studentmark >=60 && <=69) (twoone++);
^
arp.java:48: illegal start of expression
else if (Studentmark >=50 && <=59) (twotwo++);
^
arp.java:48: ')' expected
else if (Studentmark >=50 && <=59) (twotwo++);
^
arp.java:50: illegal start of expression
else if (Studentmark >=41 && <=49) (third++);
^
arp.java:50: ')' expected
else if (Studentmark >=41 && <=49) (third++);
^
arp.java:52: illegal start of expression
else if (Studentmark >=38 && <=40) (pass++);
^
arp.java:52: ')' expected
else if (Studentmark >=38 && <=40) (pass++);
^
arp.java:54: illegal start of expression
else if (Studentmark <=37 && >=0) (fail++);
^
arp.java:54: ')' expected
else if (Studentmark <=37 && >=0) (fail++);
^
arp.java:58: '}' expected
addWindowListener(new WindowAdapter() {     public void windowClosing(WindowEvent e) {       System.exit(0);     } }); // we can use pack() or setSize() here //pack(); setSize(300,200); setLocation(300,200); setVisible(true); } public static void main(String[] args) {    arp firsts = new arp();  }}
^
13 errors