我关闭表单然后重新打开它后，Java netbeans ArrayList重置为0

Question

Hi i have a main menu form and when you click customers opens a new CustomerRegistration form. The customer details are filled in and then it adds a Person of type Customer. (Person is an abstract class) then adds it to the arlCustomers Arraylist. This all works and the size of the list increases, but it is when i close that form using dispose() and go back to the main menu that the issue arrises as when i click back on the customer button the arlCustomers list size is back at 0 and I cant figure out why. I can only think that it is creating a new list each time i call the Customer Registration form but I am stumped on how to fix it.

I have tried declaring the list locally, settings the values of the list before the new CustomerRegistration window is called and moving where i declare the customerList but still no change.

MainMenu.java

  /*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package gui;

import dataModel.Consignment;
import dataModel.Customer;
import dataModel.MobileWarehouse;
import java.text.ParseException;
import java.util.ArrayList;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.DefaultListModel;

/**
 *
 * @author Rich
 */
public class MainMenu extends javax.swing.JFrame {
    private ArrayList<Customer> currentCustomers = new ArrayList();
    private Customer customer = new Customer();

    /**
     * Creates new form MainMenu
     */
    public MainMenu() {  
        initComponents();

    }

    /**
     * This method is called from within the constructor to initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is always
     * regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        lblTitle = new javax.swing.JLabel();
        btnConsignments = new javax.swing.JButton();
        btnCustomers = new javax.swing.JButton();
        btnStaff = new javax.swing.JButton();
        btnReports = new javax.swing.JButton();
        Admin = new javax.swing.JButton();
        btnSettings = new javax.swing.JButton();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setTitle("Fast Courier Service");

        lblTitle.setFont(new java.awt.Font("Arial", 1, 18)); // NOI18N
        lblTitle.setText("Demo Couriers");

        btnConsignments.setText("Consignments");
        btnConsignments.addMouseListener(new java.awt.event.MouseAdapter() {
            public void mouseClicked(java.awt.event.MouseEvent evt) {
                btnConsignmentsMouseClicked(evt);
            }
        });

        btnCustomers.setText("Customers");
        btnCustomers.addMouseListener(new java.awt.event.MouseAdapter() {
            public void mouseClicked(java.awt.event.MouseEvent evt) {
                btnCustomersMouseClicked(evt);
            }
        });

        btnStaff.setText("Staff");

        btnReports.setText("Reports");

        Admin.setText("Admin");

        btnSettings.setText("Settings");

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(layout.createSequentialGroup()
                        .addContainerGap()
                        .addComponent(btnConsignments, javax.swing.GroupLayout.PREFERRED_SIZE, 113, javax.swing.GroupLayout.PREFERRED_SIZE)
                        .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                        .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                            .addGroup(layout.createSequentialGroup()
                                .addComponent(lblTitle)
                                .addGap(0, 0, Short.MAX_VALUE))
                            .addGroup(layout.createSequentialGroup()
                                .addGap(10, 10, 10)
                                .addComponent(btnCustomers, javax.swing.GroupLayout.PREFERRED_SIZE, 113, javax.swing.GroupLayout.PREFERRED_SIZE)
                                .addGap(18, 18, 18)
                                .addComponent(btnStaff, javax.swing.GroupLayout.DEFAULT_SIZE, 116, Short.MAX_VALUE))))
                    .addGroup(layout.createSequentialGroup()
                        .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                            .addGroup(layout.createSequentialGroup()
                                .addGap(64, 64, 64)
                                .addComponent(btnReports, javax.swing.GroupLayout.PREFERRED_SIZE, 114, javax.swing.GroupLayout.PREFERRED_SIZE)
                                .addGap(38, 38, 38)
                                .addComponent(Admin, javax.swing.GroupLayout.PREFERRED_SIZE, 114, javax.swing.GroupLayout.PREFERRED_SIZE))
                            .addGroup(layout.createSequentialGroup()
                                .addGap(132, 132, 132)
                                .addComponent(btnSettings, javax.swing.GroupLayout.PREFERRED_SIZE, 114, javax.swing.GroupLayout.PREFERRED_SIZE)))
                        .addGap(0, 0, Short.MAX_VALUE)))
                .addContainerGap())
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(lblTitle)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(btnConsignments, javax.swing.GroupLayout.PREFERRED_SIZE, 36, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addComponent(btnCustomers, javax.swing.GroupLayout.PREFERRED_SIZE, 36, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addComponent(btnStaff, javax.swing.GroupLayout.PREFERRED_SIZE, 36, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addGap(28, 28, 28)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(btnReports, javax.swing.GroupLayout.PREFERRED_SIZE, 36, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addComponent(Admin, javax.swing.GroupLayout.PREFERRED_SIZE, 36, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addGap(26, 26, 26)
                .addComponent(btnSettings, javax.swing.GroupLayout.PREFERRED_SIZE, 36, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(94, Short.MAX_VALUE))
        );

        pack();
    }// </editor-fold>                        

    private void btnConsignmentsMouseClicked(java.awt.event.MouseEvent evt) {                                             
        try {
            new Consignments().setVisible(true);
        } catch (ParseException ex) {
            Logger.getLogger(MainMenu.class.getName()).log(Level.SEVERE, null, ex);
        }

    }                                            

    private void btnCustomersMouseClicked(java.awt.event.MouseEvent evt) {                                          

        try {
          **new CustomerRegistration().setVisible(true);**
        } catch (ParseException ex) {
            Logger.getLogger(MainMenu.class.getName()).log(Level.SEVERE, null, ex);
        }
    }                                         

    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        /* Set the Nimbus look and feel */
        //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
         * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
         */
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(MainMenu.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(MainMenu.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(MainMenu.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(MainMenu.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>

        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new MainMenu().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify                     
    private javax.swing.JButton Admin;
    private javax.swing.JButton btnConsignments;
    private javax.swing.JButton btnCustomers;
    private javax.swing.JButton btnReports;
    private javax.swing.JButton btnSettings;
    private javax.swing.JButton btnStaff;
    private javax.swing.JLabel lblTitle;
    // End of variables declaration                   
}

Person.java

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package dataModel;

import java.io.Serializable;
import java.text.ParseException;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;

/**
 *
 * @author Rich
 */
public abstract class Person implements Serializable {
    protected int ID = 0;
    protected String name = "Unknown";
    protected String email = "Unknown";
    protected String addressLine1 = "Unkown";
    protected String addressLine2 = "Unknown";
    protected String addressLine3 = "Unknown";
    protected String postCode = "Unknown";
    protected double costPerKg = 0.00;
    protected Role role;
    ArrayList<Customer> arlCustomers = new ArrayList<Customer>();

    public Person() {

    }

    public Person(String name) 
    {
        this.name = name;
    }

    public Person(String name, Role role, String addressLine1, String addressLine2, String addressLine3,
            String postCode) 
    {
        this.name = name;
        this.addressLine1 = addressLine1;
        this.addressLine2 = addressLine2;
        this.addressLine3 = addressLine3;
        this.postCode = postCode;

        //ID = generateID();
    }

    public Person(String name, String email, double costPerKg,  String addressLine1, String addressLine2, String addressLine3,
            String postCode) 
    {
        this.name = name;
        this.addressLine1 = addressLine1;
        this.addressLine2 = addressLine2;
        this.addressLine3 = addressLine3;
        this.postCode = postCode;
        this.costPerKg = costPerKg;

        //ID = generateID();
    }

    public void createTestData() throws ParseException
    {
        //arlCustomers = new ArrayList();

//        item = new Customer("Rich mann", "rich@email.com", 5.00, "1", "fake street", "Wadebridge", "pl27 8DD");
//        this.registerCustomer((Customer) item);
//        item = new Customer("bob mann", "rich@email.com", 5.00, "1", "fake street", "Wadebridge", "pl27 8DD");
//        this.registerCustomer((Customer) item);
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public double getCostPerKg() {
        return costPerKg;
    }

    public void setCostPerKg(double cost) {
        this.costPerKg = cost;
    }

    public int getID() {
        return ID;
    }

    public int generateID() {
        Random rand = new Random();

        int lowerBound = 0;
        int upperBound = 1000;

        int result = rand.nextInt(upperBound);

        return result;  
    }

     public ArrayList<Customer> getcustomers() {

         return arlCustomers;
    }

     public void setCustomers(ArrayList customers) 
     {
         arlCustomers = customers;
     }

    public void registerCustomer(Customer customer) {
        arlCustomers.add(customer);

    }

}

Answer 1

用您的arraylist和方法创建一个类以添加或删除等，并在arraylist和方法中添加static，并且您不需要该类的实例..并且您可以从任何类访问相同的列表。

static ArrayList<Customer> arlCustomers = new ArrayList<Customer>();