Using variable in another class

Im currently writting a Quiz program and i want to pass the varible holding the users score from the class "All.java" to "Results.java".
Any ideas how i can do this?

You can call a method in the other class and pass the value as an argument.
You can call a setter method in the other class.
You can move the knowledge and manipulation of that variable to the local class.
You can use a helper class.
All depends on what you're trying to do really, and I know that isn't much help. I struggled with the same question for a long time when I first used Java.

Similar Messages

How to update and use the values of variables of another class

I can we update or use the values of the variables of another class. For example, if we have class A
public class A //(situated in package view)
public s0,s1;
public void runFunction()
...some coding and proceedings
s0="Hi";s1"Hello";
......some coding
RequestDispatcher dispatcher = request.getRequestDispatcher("/MainUser.jsp?alert=F");
dispatcher.forward(request, response);
ARunner.jsp
<jsp:useBean id="a" class="view.A" scope="session"/>
<%
a.runFunction();
%>
MainUser.jsp
<jsp:useBean id="a" class="view.A" scope="session"/>
<%
System.out.println("S0:"+a.s0+" S1:"+a.s1); //should print S0:Hi S1:Hello, but printing S0:null S1:null
%>
A.class has some procedures and String variables which can be updated and later can be used in JSP pages. The project starts with ARunner.jsp which uses the A.class and updates the values of string variables s0 and s1of A to hi and hello respectively.And then redirects the page to MainUser.jsp.
Now what I want is ,when I call those string variables(s0 & s1 of A.class) in any another jsp likeMainUser.jsp it should give me the value of hi and hello respectively not null as it is giving right now. Could you refine the coding for this one?

public class A //(situated in package view)
public String s0,s1;
public void runFunction()
...some coding and proceedings
s0="Hi";s1"Hello";
......some coding
RequestDispatcher dispatcher = request.getRequestDispatcher("/MainUser.jsp");
dispatcher.forward(request, response);
ARunner.jsp
<jsp:useBean id="a" class="view.A" scope="session"/>
<%
a.runFunction();
%>
MainUser.jsp
<jsp:useBean id="a" class="view.A" scope="session"/>
<%
System.out.println("S0:"+a.s0+" S1:"+a.s1); //should print S0:Hi S1:Hello, but printing S0:null S1:null
%>
giving code again to remove the typing errors. Please guide.

Use methods of another class

Dear Sir/madam,
i have a question about using methods of another class. I will explane:
i have made a class which is called A. This class has some attributes (studentName and examRank) and some methods.
Now i need to made another class called B. Now i want to make an array where i can add some attributes of objects which i made of class A. How can i do that?
Kind regards

Here's a for-instance that doesn't use your exact program but demonstrates the point:
public class A
int value;
String name;
public A(int value, String name)
    this.name = name;
    this.value = value;
public int getValue()
    return value;
public String getName()
    return name;
public String toString()
    return name + ": " + value;
import java.util.Arrays;
import java.util.Random;
public class B
private static final String[] NAMES =
    "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"
private static final int MAX = 100;
private A[] myAs = new A[NAMES.length];
private Random random = new Random();
public B()
    for (int i = 0; i < myAs.length; i++)
      myAs[i] = new A(random.nextInt(MAX), NAMES);
public String toString()
return Arrays.toString(myAs);
public int getTotal()
int temp = 0;
for (int i = 0; i < myAs.length; i++)
temp += myAs[i].getValue();
return temp;
public static void main(String[] args)
B b = new B();
System.out.println(b);
System.out.println("Total: " + b.getTotal());

Using a variable from another class

hello friends, I have a class with the follow variable: dbcolTempMax, and the value of this variable I need in another class, how can do to use the value of the variable...thanks

Both people above described the solution, but from the question I take it you are somewhat new to programming. Let me give you a code example which may help.
     public class ClassWithVariable {
          private int dbcolTempMax;
          public int getDbcolTempMax() {
               return dbcolTempMax;
     public class SomeOtherClass {
          ClassWithVariable cwv = new ClassWithVariable();
          cwv.getDbcolTempMax(); // This gets the value of the variable
     }Now if the variable is static, you can provide a static "accessor" method to ge the variable. This will save you the trouble of constructing an object of the class.
Cheers,
Cypher

Using variable of one class in another class

what are the different ways in which we can access a variable defined in one class in some other class ,i am aware of making object of that class and using variable ,inheritance polymorphisms,is there any other way

learnerpuneet wrote:
i don't want to use objects of the respective class to access methods and variablesSo you've given up on OO already?
Well okay, then declare everything static and you can use class names to access methods and variables.

Using variable from another method?

Hi all, i have the code below and am getting error of:
cannot find symbol
symbol : variable myList
location: class Driver
          myList.addFirst(nodeone);
The areas noted are in bold, i want to seperate my code in the if statements into seperate methods which can be called, but when i do this i dont have access to the mylist variable. am i getting the right end of the stick? Hope someone can help. Thx
import java.util.*;
public class Driver
public static void main(String args[])
List myList = new List();
System.out.println("COMMAND LIST");
System.out.println("");
System.out.println("addFirst - Inserts a node at the beginning of the list");
System.out.println("addLast - Inserts a node at the end of the list");
System.out.println("getFirst - Returns the first node in the list");
System.out.println("getLast - Returns the last node in the list");
System.out.println("");
     Scanner input = new Scanner(System.in);
     String command;
     System.out.print("Please enter a command: ");
     command = input.next();
     if (command.equals("addFirst"))
          inputAddFirst();
          else if (command.equals("addLast"))
                    String nodeName;
                    System.out.print("Enter name of Last Node: ");
                    nodeName = input.next();
                    Node nodelast = new Node(nodeName);
                    myList.addLast(nodelast);
                    System.out.println("Setting Last Node");
          public static void inputAddFirst()
          String nodeName;
          Scanner input = new Scanner(System.in);
          System.out.print("Enter name of First Node: ");
          nodeName = input.next();
          Node nodeone = new Node(nodeName);
          myList.addFirst(nodeone);
          System.out.println("Setting First Node");
}

You can pass myList to the method that uses it.
Or, you can make inputAddFirst just return an object, and add it in main.
Or you could make myList a field, rather than a local variable. If you do that however, you'd probably want the stuff in main to go into a new, non-static method. Also you shouldn't use fields for what are in essence temporary variables, so ask yourself whether myList really represents the ongoing state of whatever object it's in.

How to call a variable in another class????

if i have two classes in a package. From one class, how do i get the value of one of the variable in the other class.
For example;
Class A have a variable call totalNum which have a value initialise.
Class B wan to get the value variable totalNum in class A.
So do i go abt calling it?
Cheers

For example;
Class A have a variable call totalNum which have a
value initialise.
Class B wan to get the value variable totalNum in
class A.Your explanation is far from clear. Is the variable in class A a field? If yes, is it a static field? Is it declared public, private, etc.?
If you don't understand the above questions, you should do the following:
1) Learn the basics of the Java language from the Java Tutorial and/or from an entry-level book: http://java.sun.com/docs/books/tutorial/
2) Post future question in the New To Java Technology forum.

Using variables in different classes

Hi,
A very basic question!
i've got a 2d array in one class, which I want another class to be able to see. Is there any way I can do this in Java - if so, how? If not, is there a way around this?
Thanks

Or don't put it in a class, put it into an interface instead; have both classes impelement it.
~Bill

To use a static variable in another class,but report NullPointerException

when TableMain is running,I run testRecord so that let TableMain add a occur informatin and
happened time in a row in TableMain,but when I run testRecord,java report a NullPointerException and I dont know how to solve this problem,thanks for helping me to check my code;(error report info is in end)
import java.awt.event.*;
import javax.swing.table.*;
import java.io.*;
public class TableMain extends JFrame{
JTable table;
static OwnModel model;
String[] columnHeader={"occur","time"};
class OwnModel extends DefaultTableModel{
public OwnModel(Object[] columnNames,int numRows){
super(columnNames,numRows);
public boolean isCellEditable(int row,int column){
return false;
public TableMain(){
model=new OwnModel(columnHeader,0);
table=new JTable(model);
JScrollPane scroll=new JScrollPane(table);
JButton save=new JButton("save record");
JButton delete=new JButton("delete record");
JPanel buttons=new JPanel();
buttons.add(save);
buttons.add(delete);
JLabel sign=new JLabel("occur record");
Container cp=getContentPane();
cp.add(BorderLayout.NORTH,sign);
cp.add(BorderLayout.CENTER,scroll);
cp.add(BorderLayout.SOUTH,buttons);
this.setSize(300,500);
this.setVisible(true);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
public static void main(String[] args){
new TableMain();
import java.util.Vector;
import java.util.Calendar;
import java.text.SimpleDateFormat;
public class testRecord{
public static void main(String[] args){
SimpleDateFormat simpledf=new SimpleDateFormat("yyyy/MM/dd hh:mm:ss");
String tableName="friends";
Calendar occurtime=Calendar.getInstance();
Vector record=new Vector();
record.add("send 'desc' sql, "+"operated table is :"+tableName);
record.add(simpledf.format(occurtime.getTime()));
System.out.println("model is "+Guide.model);
System.out.println("record is "+record);
Guide.model.addRow(record);
error report:
model is null
record is [send 'desc' sql,operated table is :friends, 2004/05/26 11:39:03]
Exception in thread "main" java.lang.NullPointerException
at testRecord.main(testRecord.java:14)

but I just use this constructor once,never use twice
with same jvm;I thinks my idea is not too very badIt's a public constructor (if I'm looking in the right
place) - it could be called from anywhere. To
intialize a static variable outside the declaration,
use a static initializer:private static String whatever;static {
whatever = "whatever";
}Or simply (in this case):private static String whatever = "whatever";

How can I call a variable from another class

hi
If I have two classes : one and two
In class two I have a variable called : action
In class one I want to check what is the value of action.
How can I call action?

Thank you scorbett
what you told me worked fine, but my problem is that MyClass2 is an application by itself that I don't want to be executed.
Creating myClass2 as in the following:
MyClass2 myClass2 = new MyClass2();
[/code]
executes myClass2.
Can I prevent the exectuion of MyClass2, or is there another way to call the variable (action)?

J2ME error to get value from variable in another class

hi,,
i write code for a mobile application like a tour guide..
i had create 5 class for this application, KutaBeachDictionary MIDlet class, ListMainMenu List class, ListMenuHotel List class, HotelDes01 Form class and the last Hotel class that store all information.
the problem is, i have [choose] variable in ListMenuHotel that contain getSelectedIndex() value, i want to take [choose] value from ListMenuHotel class to [index] variable in HotelDes01, so it determine the name of hotel that will display in form.but the index always 0 although i had choosen different menu from ListMenuHotel..
here is all code
in MIDlet class
import javax.microedition.lcdui.Alert;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;
import javax.microedition.midlet.MIDlet;
public class KutaBeachDictionary extends MIDlet {
    public KutaBeachDictionary() {
        lstMenuUtama = new ListMenuUtama(this);
        lstMenuHotel = new ListMenuHotel(this);
        htlDes1 = new HotelDes01(this);
        frmLoading = new FormLoading(this);
    public Display getDisplay() {
        return Display.getDisplay(this);
    public void exitMIDlet() {
        switchDisplayable(null, null);
        destroyApp(true);
        notifyDestroyed();
    public void startApp() {
        if (midletPaused) {
            resumeMIDlet();
        } else {
            initialize();
            startMIDlet();
        midletPaused = false;
        getDisplay().setCurrent(frmLoading);
        new Thread(frmLoading).start();
        frmLoading.done = false;
        frmLoading.gLoading.setValue(0);
    public void pauseApp() {
        midletPaused = true;
    public void destroyApp(boolean unconditional) {
    private boolean midletPaused = false;
    public ListMenuHotel lstMenuHotel;
    public ListMenuRestaurant lstMenuRestaurant;
    ListMenuUtama lstMenuUtama;
    FormAbout frmAbout;
    public HotelDes01 htlDes1;
    FormLoading frmLoading;
}the code in ListMenuHotel
import java.io.IOException;
import javax.microedition.lcdui.Command;
import javax.microedition.lcdui.CommandListener;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.Image;
import javax.microedition.lcdui.List;
import javax.microedition.lcdui.Ticker;
public class ListMenuHotel extends List implements CommandListener {
    Hotel objHotel = new Hotel();
    ListMenuHotel(KutaBeachDictionary run) {
        super("List Hotel", List.IMPLICIT);
        this.run = run;
        try {
            btnImage = Image.createImage("/btnImage.png");
        } catch (IOException e) {
        tickerMenu = new Ticker("Daftar Hotel di Pantai Kuta Bali");
        setTicker(tickerMenu);
        for (int i = 0; i < objHotel.namaHotels.length; i++) {
            append(objHotel.namaHotels, btnImage);
addCommand(new Command("Select", Command.OK, 0));
addCommand(new Command("Back", Command.BACK, 0));
setCommandListener(this);
public void commandAction(Command cmd, Displayable dsp) {
if (cmd == SELECT_COMMAND) {
choose = getSelectedIndex();
Display.getDisplay(run).setCurrent(run.htlDes1);
switch (cmd.getCommandType()) {
case Command.BACK:
Display.getDisplay(run).setCurrent(run.lstMenuUtama);
break;
public int getChoose() {return choose;}
private KutaBeachDictionary run;
private Image btnImage;
private Ticker tickerMenu;
private int choose;
the code in HotelDes01 Form classimport java.io.IOException;
import javax.microedition.lcdui.Command;
import javax.microedition.lcdui.CommandListener;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.Form;
import javax.microedition.lcdui.Image;
import javax.microedition.lcdui.ImageItem;
public class HotelDes01 extends Form implements CommandListener {
private KutaBeachDictionary run;
private int index;
private Hotel isiHotel = new Hotel();
public HotelDes01(KutaBeachDictionary run) {
super("Inna Kuta Hotel");
index = run.lstMenuHotel.getChoose(); //here is the problem..the value remain 0 althought i choose another??!!
this.run = run;
Image imgHotel = null;
String namaHotel = "\n" + isiHotel.namaHotels[index] + "\n";
try {
imgHotel = Image.createImage("/HotelImage/interface/htlDes1.png");
} catch (IOException e) {
append(new ImageItem(null, imgHotel, ImageItem.LAYOUT_CENTER, null));
append(namaHotel);
addCommand(new Command("Back", Command.BACK, 0));
setCommandListener(this);
public void commandAction(Command cmd, Displayable dsp) {
switch (cmd.getCommandType()) {
case Command.BACK:
Display.getDisplay(run).setCurrent(run.lstMenuHotel);
break;
can someone fix the code,, i had tried so many ways,,but completely failure.. T_T
Edited by: diaca on Mar 22, 2010 7:55 AM
Edited by: diaca on Mar 22, 2010 8:01 AM

hei bro,i had solved the problem :)
the problem is , i had constructed the form of hotelDes01 each time the program starting with this code
public class KutaBeachDictionary extends MIDlet {
    public KutaBeachDictionary() {
        //.. declaring several new object
        htlDes1 = new HotelDes01(this);
    //..another procedure like startApp, pauseApp, etc
public HotelDes01 htlDes1;
}i think if i declare this class in the beginning it never updated the index value
so i delete the code above, and i declare the htlDes1 in the listMenuHotel like this:
public class ListMenuHotel extends List implements CommandListener {
    //..several code just like before
public void commandAction(Command cmd, Displayable dsp) {
        if (cmd == cmdSelect) {
           objHotel.setChoose(getSelectedIndex()); //i change the code like this
           showInformation();
        if (cmd == cmdBack) {
            Display.getDisplay(run).setCurrent(run.lstMenuUtama);
    public void showInformation() {
        HotelDescription htlDes1 = new HotelDescription(run); //reconstruct the object in the class ListMenuHotel
        Display.getDisplay(run).setCurrent(htlDes1); //display the object
    }so the form of hotelDes01 now always reconstruct whenever user change the election in ListMenuHotel class and now index value get updated.. :D
thanks for trying to fix the code qnat..
this is my coursework, so i get to finish it ASAP..

Reading variable from another class

If you have two java classes both inside the same java package.
And you declared a variable for example
String bob;
bob = "hello world?"How would you make it so that the other file could then output this value
System.out.print(bob);Would you have to make the variable public and then something else?

Are you working with a main and subclass then?
Why not just write a String method and use it from the main class
public String string()
String bob = "Hello word"
return bob;
Then in your main class just create a object of the subclass
Subclass obj = new Subclass();
The just use System.out.println(obj.string());
i guess this would work also....?

Using HashMaps from another class

I'm trying to use a HashMap to store a person with a given Id. When i create a HashMap as part of a main method and use the put method on that HashMap everything goes fine ie:
Map myMap = new HashMap();
Person james = new Person)("James", "Smith");
myMap.put(1,james);However, when I use a HashMap as part of one class and attempt to call it in another using a simple add method I get a null pointer exception. For example, I have the class People which is basically:
import java.util.*;
public class People
    private Map myPeople;
    public People()
        Map myPeople = new HashMap();
    public void addPerson(int id, Person p)
        PeopleTable.put(id,p);
}I then make a call to this using a separate main method
Person james = new Person ("James","Smith");
People myFamily = new myFamily();
myFamily.addPerson(1,james);but get a null pointer exception. I can't see anything glaringly obvious that i'm getting wrong, but i've just started using HashMaps so I may be missing something.
Any insight would be greatly appreciated!
Thanks,
Nick

nickd_101 wrote:
However, when I use a HashMap as part of one class and attempt to call it in another using a simple add method I get a null pointer exception. For example, I have the class People which is basically:
import java.util.*;
public class People
private Map myPeople;
public People()
Map myPeople = new HashMap(); //*** You're declaring the map again here, don't do this.
public void addPerson(int id, Person p)
PeopleTable.put(id,p);
You're declaring the map twice, once at the top of the class, which is good, and once again in the constructor, which is very bad since the class's hashmap never gets constructed. Don't do this.
The constructor should be:
    public People()
        myPeople = new HashMap(); // ** better
    }

How to call a variable from another class?

Greetings
I�m designing a program that is called Senior.java, and I want to design it�s menus, for simplicity in reading the code, I want to write a separate java file for each menu. For example I want a file.java, edit.java etc�.
Since I�m not a professional I�m having problems in calling the variable �bar�, that I created in senior.java,
In Senior.java I have :
JMenuBar bar = new JMenuBar();
setJMenuBar( bar );
In fileMenu.java I want to add file menu to the menu bar �bar�:
bar.add( fileMenu );
When I compile the fileMenu.java I got a �cannot resolve symbol � message, where symbol is the variable bar.
Can you please help me, knowing that i'm using SDK1.4.1?

Sun has recommendations for naming conventions. Class names should start with a capital letter. You should avoid using class names that are the same as classes provided in the SDK. Following these conventions will make it easier for people to help you. For example, you should not use file, nor should you use File. It's better to use MyFile, replacing My with something that makes sense to your application (SeniorFile?).
Also, check the Formatting Help link when posting for a desciption on how to use the code tags for posting code.
1. You need to establish references between your classes. One way is to have a constructor that has a JMenuBar argument.
2. You can not add a file to a JMenuBar because a JMenuBar adds a JMenu. I don't think you want file to extend JMenu. It may be better for file to have a JMenu.
I haven't tried to compile this code so no guarantees - just trying to show you an approach.
public class Senior extends JFrame {
   public Senior() {
      JMenuBar bar = new JMenuBar();
      MyFile file = new MyFile(bar);
//whatever else you need
public class MyFile {
   public MyFile(JMenuBar mbar) {
      JMenu menu = new JMenu();
      mbar.add(menu);

How to get variable from another class?

I have 2 classes. In first I have int variable. In second class I need to get this variable value. How I can make it?
import javax.microedition.lcdui.*;
import java.io.*;
import java.util.*;
public class ChooseLessons extends Form implements CommandListener, ItemStateListener
     ChoiceGroup lessons;     // Choice Group of preferences
     Dictionary     dictionary;
     int volumeSize;
     ChooseLessons(Dictionary dictionary)
          int volumeSize = 15;
     public void commandAction(Command c, Displayable s)
          if (c == Dictionary.BEGIN_CMD) {
               new TeachForm(dictionary, this);
import javax.microedition.lcdui.*;
import java.util.*;
public class TeachForm extends Form implements CommandListener
     Dictionary               dictionary;
     ChooseLessons          lessons;
     TeachForm(Dictionary dictionary, ChooseLessons lessons) {
          super(Locale.WORD);
          this.dictionary = dictionary;
          this.lessons = lessons;
          lessons.volumeSize(); // HERE I NEED VARIABLE VALUE FROM PREVIOUS CLASS
}Edited by: Djanym on Mar 16, 2009 4:43 PM

This is a classic problem that coders run into when trying to get their head around object-oriented programing. Since you have a class that should be modeled after a real world object, as far as that object is concerned, no one else needs to know the details of it - without asking nicely. This is where you should set up some getters and setters, which are methods that allow fields in a class to reveal themselves or allow their states to be changed in a orderly fashion.
There are a number of fields that never need to be known outside of the class. Then there are some fields you would like to let people know about, but don't want them to have the ability to change them. In the example below, there are to getter methods allow return of the necessary fields. If you made these public, there is a possibility that someone utilizing this field may change it outside of its intended use, or access them without them being ready for public consumption.
Class test {
//These private variables are only visible from the class
private int grade1 = 0;
private int grade2 = 0;
private int grade3 = 0;
private float average = 0;
private int gradeboost = 0;
//This method sets the gradeboost field to one desired by the instructor
void setboost(int boost) {
gradeboost = boost;
//These methods accept test scores and compute the average for three test
//Notice that the calculated average may not be the true average of the three test scores
//because of the possibility of gradeboost calculation being greater than 1
void test1(int score) {
         grade1 = score;
         average = (grade1 + grade2 + grade3 + gradeboost)/3;
void test2(int score) {
         grade2 = score;
         average = (grade1 + grade2 + grade3 + gradeboost)/3;
void test3(int score) {
         grade3 = score;
         average = (grade1 + grade2 + grade3 + gradeboost)/3;
//This is a getter method, which provides read access to the private variable average
//If someone just had public access to the grades and wanted to take their own average
//They would miss how the gradeboost field affects the final outcome.
float getAverage() {
    return average;
//Here is a getter method, which accepts an argument to determine which test score to return
//Notice that this isn't the true testscore, but it has been modified by the gradeboost field.
//If the user had public access to the true testscore, it wouldn't take into account the gradeboost calculation!!
//This is how a getter can control exactly what a user has access to.
float get testScore(int test) {
float testresult = 0;
if (test = 1) {
       testresult = (grade1+ gradeboost) / 3;
if (test = 2) {
       testresult = (grade2+ gradeboost) / 3;
if (test = 3) {
       testresult = (grade3+ gradeboost) / 3;
return testresult;
}

Using variable in another class

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