How to check value of a variable

Question

hi, all
I have 2 class: A and B
class A :
class A {
     static int count = 0;
     public int incre() {
          count++;
          return count;
     public int decrea() {
          count--;
          return count;
}class B:
class B {
     public void doSomething() {
          if (A.count == 0) {
               // I can get value because it have default value in class A
          } else {
               // I don't know when A.count increase or decrease by another    class
}When B start will call to use class A, after B finish, another class will call to use and can increase or decrease count.
When count is changing by another class, I (class B) want to know what is the value of count variable
Please help, thanks many

Answer 1

Depending on the actual requirement, this should be a
good exercise for using java.util.Observer and
Observable pair. See the API documentation for these
two. And, try describe your application requirement
in more detail.Thanks for your reply, but I can not use Observer/Observable to solve
To me attach example code, please see it again
class MainFrame:
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
public class MainFrame extends JFrame {
     private JButton button;
     public MainFrame(){          
          this.setTitle("Please help me");
          this.setSize(300, 200);
          button = new JButton("Open");
          button.addActionListener(new ActionListener(){
               public void actionPerformed(ActionEvent e) {
                    Object o = e.getSource();
                    if(o == button){                         
                         ChangeValue c = new ChangeValue();
                         c.show();
          this.getContentPane().setLayout(new FlowLayout());
          this.getContentPane().add(button);
          this.setDefaultCloseOperation(EXIT_ON_CLOSE);
          this.setVisible(true);
     public void howTo(){
          System.out.println("get abc variable from ChangeValue.java = "+ChangeValue.abc);
          if(ChangeValue.abc > 0){
               // I want to get value  of count variable here. But i can not
               // Please help
     public static void main(String [] args){
          MainFrame m = new MainFrame();
          m.show();
          m.howTo();          
}class ChangeValue:
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Observable;
import java.util.Observer;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
public class ChangeValue extends JFrame{
     JButton b = new JButton("Exit");
     public static int abc = 0;
     public ChangeValue(){     
          abc ++;
          this.setTitle("Child");
          this.setSize(250, 100);
          this.getContentPane().setLayout(new FlowLayout());          
          b.addActionListener(new ActionListener(){
               public void actionPerformed(ActionEvent e) {
                    if(e.getSource() == b){
                         setVisible(false);     
          this.getContentPane().add(new JLabel("You have just increase abc variable"));
          this.getContentPane().add(b);
          this.setVisible(true);
          System.out.println("You have just increase abc variable (from class ChangeValue) = " + abc);
}When MainFrame load, you press button "Open",
this button will call class ChangeValue and increase abc variable to 1
You press button Exit on ChangeValue and press button Open on MainFrame again, abc will increase to 2.
Please see howTo() method in MainFrame, i want to get value of abc variable (= 1, 2 ...) but I can not.
(See log for more detail)
Could you please help me to find the way to solve this problem !
thanks many