尽管添加了元素，但是链表为空

Question

I created a "frame1" that contains a button , so if I click on that button , button action performed method will check if the LinkedList is empty , if is ,it will set the "addEmployee" frame visible which contains radioButton calls addEmployees_Auto, and when clicked , it will invoke method "add_Auto" from frame1 . This should fill the linkedList in frame1, but if I re-clicked on the button again , the LinkedList is empty again. why? shouldn't the LinkedList be fill ??

this is "frame1"

public class Frame1 extends javax.swing.JFrame {

    LinkedList <Employee>list2=new LinkedList <Employee>();
        ....

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {

    System.out.println("size="+list2.size());

    if(list2.isEmpty())
      new AddEmployees.setVisible(true);
}

public void addEmployees_Auto()
     {

        list2.add(new Employee(20910733,"Ahmed","Manager",2700));
        list2.add(new Employee(20910835,"Omar","Teaacher",2100));
        list2.add(new Employee(20910674,"Mohammed","Manager",3000));
        list2.add(new Employee(20910955,"Kareem","",2700));
        list2.add(new Employee(20910921,"Ameer","teacher",2500));

     }
}

AddEmployee frame :

public class AddEmployees extends javax.swing.JFrame {
             ...

    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt)    
 {                                         

     if(jRadioButton2.isSelected()){

        new Frame1().addEmployees_Auto();
        this.setVisible(false);
  }

}       

Answer 1

I think this is because you are doing:

new Frame1()

every time in your AddEmployees class, so each time a new linked list is being created, which is always going to be empty. You need to pass in a reference to the calling instance of Frame1 , such as

new AddEmployees(this)

from the Frame1 class, and add the appropriate constructor to your AddEmployees class, eg

public AddEmployees(JFrame parent) { ... }