遍历 List 但它只显示最后一项

Question

What I am trying to achieve is have one JLabel to display multiple items from a List .

I have defined the list as below but when I test the code my method to iterate through the list, after a button click, only shows the last item in the list which is "DONE!" .

I am trying to accomplish displaying only the next item in the list after each button click on one JLabel .

public class ScoutGUI extends javax.swing.JFrame {

    /**
     * Creates new form ScoutGUI
     */
    List<String> strings = Arrays.asList("Do you mind Clutter in Room?", "Do you mind alarm clocks?","Do you mind loud visitors?","Can you sleep with lights on?","Do you mind noise past Midnight?",
        "Do you consider yourself as an introvert?", "Do you consider yourself as an extrovert?","Do you like to go to parties?","Do you drink alcoholic beverages?(21+)", "DONE!");


    ArrayList<Student> obj = new ArrayList<>();
    String name , email , gender , major , year , language , building ;
    int id , i;
    public ScoutGUI() {
        initComponents();
    }

    public ScoutGUI(int a) {
        i = a;
        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() {

        panel1 = new java.awt.Panel();
        jButton1 = new javax.swing.JButton();
        jButton2 = new javax.swing.JButton();
        jLabel1 = new javax.swing.JLabel();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        jButton1.setFont(new java.awt.Font("Courier", 0, 13)); // NOI18N
        jButton1.setText("NO");
        jButton1.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButton1ActionPerformed(evt);
            }
        });

        jButton2.setFont(new java.awt.Font("Courier", 0, 13)); // NOI18N
        jButton2.setText("YES");
        jButton2.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButton2ActionPerformed(evt);
            }
        });

        jLabel1.setFont(new java.awt.Font("Courier New", 1, 18)); // NOI18N
        jLabel1.setBorder(javax.swing.BorderFactory.createMatteBorder(1, 1, 1, 1, new java.awt.Color(204, 255, 153)));

        javax.swing.GroupLayout panel1Layout = new javax.swing.GroupLayout(panel1);
        panel1.setLayout(panel1Layout);
        panel1Layout.setHorizontalGroup(
            panel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(panel1Layout.createSequentialGroup()
                .addGap(71, 71, 71)
                .addComponent(jButton1)
                .addGap(94, 94, 94)
                .addComponent(jButton2)
                .addContainerGap(129, Short.MAX_VALUE))
            .addGroup(panel1Layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(jLabel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addContainerGap())
        );
        panel1Layout.setVerticalGroup(
            panel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(panel1Layout.createSequentialGroup()
                .addGap(26, 26, 26)
                .addComponent(jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, 159, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addGap(18, 18, 18)
                .addGroup(panel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jButton1)
                    .addComponent(jButton2))
                .addContainerGap(68, Short.MAX_VALUE))
        );

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(panel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(panel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
        );

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

    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        // TODO add your handling code here:
        //skip and never

        buttonpressActionPerformed();

    }                                        

    private void jButton2ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        // TODO add your handling code here:
        //match and update

        buttonpressActionPerformed();

    }                                        

    private void buttonpressActionPerformed() { 


       // int i = 0;


        Iterator<String> iterator = strings.iterator();


        //for (String strin : strings)  
        while (iterator.hasNext())

        {   

            //if (jButton2.isSelected() || jButton1.isSelected())
            //{
            jLabel1.setText(iterator.next());
            //}       

        }

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

    // Variables declaration - do not modify                     
    private javax.swing.JButton jButton1;
    private javax.swing.JButton jButton2;
    private javax.swing.JLabel jLabel1;
    private java.awt.Panel panel1;
    // End of variables declaration                   
}

Answer 1

Your current code always overrides the current text in the JPanel, and it does that so fast, that you don't see it. Instead of using the Iterator, get the next item in the list by defining an int variable that gets incremented every press.
The index variable is a public int in this example:

 jLabel1.setText(strings.get(index));
 if (index < strings.size()-1) 
        index++;

No loops, that's everything needed in your method.

Answer 2

In order to locate next string from collection, you need somehow know about current item.

One approach is to store index (or iterator) in a field:

List<String> strings=<...>
// 1. store index    
int sentenceIndex = 0; 
// 2. store iterator. You could get ConcurrentModificationException if change list and then use iterator.
Iterator<String> iterator = strings.getIterator();
private void buttonpressActionPerformed() { 
// 1. use index. 
if (sentenceIndex < strings.size()-1) { // avoid IndexOutOfBoundException
  String nextSentence = strings.get(sentenceIndex++);
}
// 2. use iterator
if (iterator.hasNext()) {
  String nextSentence = iterator.next();
}

But in fact you don't need to store something:

// 3. calculate current index
String currentSentence = jLabel1.getText();
int currentIndex = strings.indexOf(currentSentence);
int nextIndex = incrementIndex(currentIndex);
String nextSentence = strings.get(nextIndex );

Note that I suggest new method incrementIndex . In it you could add not only lenght check but also jumping from last element to the first or just random selecting.

Each method has pro and contras:

1. index require boundary checks

2. iterator limits list updating

3. index calcucaliton also require boundary checks and label1 should have correct initial value

   I would prefer storing index but it's your choice