单击按钮时依次显示每个数组列表元素

Question

我使用 Java 制作了JFrame。

我得到一个arraylist =[1,2,3,4]，每当我单击下一个按钮时，列表中的下一个数字应该显示在JLabel 中。 我已经编写了代码，但问题是当我运行文件时它显示 "1" 并且当我单击下一个按钮时它在标签中显示 4 。 2 和 3 未显示。

我该如何解决这个问题？

public class prac extends javax.swing.JFrame {
    ArrayList<Integer>arr=new ArrayList<>();
        

    /**
     * Creates new form prac
     */
    
    public prac() {
        initComponents();
        arr.add(1);
        arr.add(2);
        arr.add(3);
        arr.add(4);
        String s=String.valueOf(arr.get(0));
        jLabel1.setText(s);
    }
    
    

    /**
     * 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() {

        jLabel1 = new javax.swing.JLabel();
        jButton1 = new javax.swing.JButton();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        jButton1.setText("next");
        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()
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(layout.createSequentialGroup()
                        .addGap(42, 42, 42)
                        .addComponent(jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, 281, javax.swing.GroupLayout.PREFERRED_SIZE))
                    .addGroup(layout.createSequentialGroup()
                        .addGap(124, 124, 124)
                        .addComponent(jButton1, javax.swing.GroupLayout.PREFERRED_SIZE, 73, javax.swing.GroupLayout.PREFERRED_SIZE)))
                .addContainerGap(77, Short.MAX_VALUE))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(41, 41, 41)
                .addComponent(jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, 69, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 86, Short.MAX_VALUE)
                .addComponent(jButton1)
                .addGap(81, 81, 81))
        );

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

    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        // TODO add your handling code here:
        //System.out.println(lis);
        int i;
        
        for(i=1;i<arr.size();i++)
        {
            String d=String.valueOf(arr.get(i));
           jLabel1.setText(d);
        }
    }                                        

    /**
     * @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(prac.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(prac.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(prac.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(prac.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 prac().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify                     
    private javax.swing.JButton jButton1;
    private javax.swing.JLabel jLabel1;
    // End of variables declaration                   
}

运行文件后

点击下一步后

Answer 1

如果您真的只想循环遍历数字 1 到 4，则根本不需要数组。您只需要读取标签的当前值并将其递增，如果递增为 5，则将其更改回 1。

private static void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
    Integer i = Integer.parseInt(jLabel1.getText());
    i++;
    if (i == 5) i = 1;
    jLabel1.setText(i.toString());
}

但是，如果您确实需要从数组中读取值，因为它可能不是连续的，您可以在数组中查找当前值并增加索引。

private static void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
    Integer i = Integer.parseInt(jLabel1.getText());
    int index = arr.indexOf(i);
    index++;
    if (index == 3) index = 0;
    jLabel1.setText(arr.get(index).toString());
}

注意：如果数组中有重复值，第二种方法将不起作用。

Answer 2

只跑过 1-4

如 cmets 中所述，jButton1ActionPerformed 方法中的 for 循环不正确。你应该：

• 取现有值
  

• 加一
  

• 如果超过限制，则重置为 1
  

   private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
       int limit = arr.size(); //or just 4?
       String d=jLabel.getText(); //take old one
       //if no value was set before..
       if (d.length()==0) d = "0";
       int num = Integer.parseInt(d) + 1; //takes next one
       if (num>limit) num = 1; //resets to 1 if needed
       jLabel1.setText(""+num);
   }  
  

从 ArrayList 中取值

从ArrayList 获得类似的计划，但不仅仅是 +1，你：

• 在列表中查找旧值的索引，
• 索引加一，
• 如果超出范围，则重置为 0，
• 将 JLabel 的文本设置为新索引处 List 的值

.

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
    String d = jLabel1.getText(); //take from old one
    //if no value was set before, just sets to -1, so after +1 would be at idx 0
    if (d.length()==0) d = "-1";
    int parsedOldValue = Integer.parseInt(d); //gets int from String
    int newIndex = arr.indexOf(parsedOldValue) + 1; //takes next index
    if (newIndex >= arr.size()) newIndex = 0; //if exceeds, takes 0th
    jLabel1.setText(""+arr.get(newIndex));
}