从 ArrayList 一无所获的公共类

Question

我正在开发一个用于编程练习的 GUI。我期望 GUI 做的是 CLASSTEST2 将在单击按钮时在 ArrayList (arrayList1) 中添加项目，而另一个 GUI (CLASSTEST1) 将通过公共打印该 arraylist 中的第一个项目和 arraylist 本身CLASSTEST1 中的无效函数 printArrayList ()。

问题是，当我调用或运行打印上述内容的函数时，它显示 arrayList 是空的，并且即使项目已经添加到 arraylist 上，它也会抛出 IndexOutOfBoundsException。我有什么遗漏吗？

CLASSTEST1：

public class CLASSTEST1 extends javax.swing.JFrame {
    public CLASSTEST1() {
        initComponents();
    }

    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        jButton1 = new javax.swing.JButton();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        jButton1.setText("jButton1");
        jButton1.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButton1ActionPerformed(evt);
            }
        });

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(146, 146, 146)
                .addComponent(jButton1)
                .addContainerGap(177, Short.MAX_VALUE))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(128, 128, 128)
                .addComponent(jButton1)
                .addContainerGap(140, Short.MAX_VALUE))
        );

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

    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        CLASSTEST2 classTest2 = new CLASSTEST2();
        System.out.print(classTest2.arrayList1.get(0));
    }                                        

    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new CLASSTEST1().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify                     
    private javax.swing.JButton jButton1;
    // End of variables declaration  

CLASSTEST2：

import java.util.ArrayList;

/**
 *
 * @author Private
 */
public class CLASSTEST2 extends javax.swing.JFrame {

    ArrayList arrayList1 = new ArrayList();
    public CLASSTEST2() {
        initComponents();
    }


    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        addToArrayListTEXT = new javax.swing.JTextField();
        addToArrayListBTN = new javax.swing.JButton();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        addToArrayListBTN.setText("jButton1");
        addToArrayListBTN.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                addToArrayListBTNActionPerformed(evt);
            }
        });

        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()
                        .addGap(82, 82, 82)
                        .addComponent(addToArrayListTEXT, javax.swing.GroupLayout.PREFERRED_SIZE, 169, javax.swing.GroupLayout.PREFERRED_SIZE))
                    .addGroup(layout.createSequentialGroup()
                        .addGap(122, 122, 122)
                        .addComponent(addToArrayListBTN)))
                .addContainerGap(90, Short.MAX_VALUE))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(86, 86, 86)
                .addComponent(addToArrayListTEXT)
                .addGap(18, 18, 18)
                .addComponent(addToArrayListBTN)
                .addContainerGap(140, Short.MAX_VALUE))
        );

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

    private void addToArrayListBTNActionPerformed(java.awt.event.ActionEvent evt) {                                                  
       arrayList1.add(addToArrayListTEXT.getText());
      
    }                                                 
    
    public void printArrayList (){
        System.out.println(arrayList1.get(0));
        System.out.println(arrayList1);
    }
   
    /**
     * @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(CLASSTEST2.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(CLASSTEST2.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(CLASSTEST2.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(CLASSTEST2.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 CLASSTEST2().setVisible(true);
            }
        });
    }

这些小类只是我在大型项目中遇到的一个问题的代表，但我不能在这里发布，因为它太大了，但是这个问题和类几乎总结了它。

Answer 1

与CLASSTEST2中的ArrayList类似，需要让CLASSTEST2实例成为CLASSTEST1的成员，而不是每次都新建一个：

public class CLASSTEST1 extends javax.swing.JFrame {

    private CLASSTEST2 classTest2;

    private void initComponents() {
      
       classTest2 = new CLASSTEST2();
    }

    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        System.out.print(classTest2.arrayList1.get(0));
    }   

    java.awt.EventQueue.invokeLater(new Runnable() {
        public void run() {
            classtest2.setVisible(true);
        }
    });
}