java - how can I pass value from textfield to object or file(serializable file)? -

ive got layout codes ready(i have 3 classes). after inputed first name, last name, address, age , salary clicked button "save", should save on employee.ser file , should not overwrite every time save input information.

import javax.swing.*;     import java.awt.*;     import java.io.*;     import java.util.*;     public class employeeapp extends jframe     {         private arraylist <employee> list;      public employeeapp() {     list = new arraylist<employee>(); }  jpanel panel; jlabel label; jtextfield field; jframe frame; jbutton save;   public void initialize() {     panel = new jpanel();     frame = new jframe("mark");     save = new jbutton("save");     frame.add(borderlayout.south, save);     getcontentpane().setlayout(new flowlayout());     frame.setdefaultcloseoperation(jframe.exit_on_close);     frame.setsize(350,350);     frame.setvisible(true);     panel.setlayout(new gridlayout(12,0));      jlabel label = new jlabel("enter first name ");     field = new jtextfield(20);     frame.add(borderlayout.center,panel);     panel.add(label);     panel.add(field);       label = new jlabel("enter last name ");     field = new jtextfield(20);     panel.add(label);     panel.add(field);      label = new jlabel("enter adress ");     field = new jtextfield(20);     panel.add(label);     panel.add(field);      label = new jlabel("enter age ");     field = new jtextfield(20);     panel.add(label);     panel.add(field);      label = new jlabel("enter salary ");     field = new jtextfield(20);     panel.add(label);     panel.add(field);   }   public void start() {     initialize(); }  private void load() {     file empfile = new file("employee.ser");     if(empfile.exists())     {         try         {             fileinputstream fis = new fileinputstream(empfile);             objectinputstream ois = new objectinputstream(fis);             employee emp = null;             while((emp = (employee) ois.readobject()) != null)             {                 list.add(emp);             }         }         catch(exception e){}     } }     } 

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import java.io.*;      public class employee implements serializable     {      private string firstname; private string lastname; private string address; private int age; private double salary;         public void setfirstname(string first) {             firstname = first;     }     public string getfirstname() {             return firstname;     }      public void setlastname(string last) {             lastname = last;     }     public string getlastname() {             return lastname;     }      public void setaddress(string ad) {             address = ad;     }     public string getaddress() {             return address;     }      public void setage(int ag){         age = ag;     }     public int getage(){         return age;     }      public void setsalary(double sal){         salary = sal;     }     public double getsalary(){         return salary;     }     }     

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     public class employeelauncher     {         public static void main(string[] args) throws exception         {             employeeapp em = new employeeapp();             em.start();         }     }     

1. add actionlistener save button.
2. override actionperformed handle save action (get values textfields).
3. load object inside file (what done in load())
4. create fileoutputsteram , use writeobject() method of objectoutputstream write objects in list.