如何在Java中从另一个类更新jLabel或setText？

Question

我试图创建一个JFrame，其中有JLabel和按钮，并在另一个类中创建了一个方法PuttextNow，该方法将文本设置为JLabel。我已经读到，它应该使用多线程，这是更复杂的在我的部分。以下是我的代码：

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
    NewClass nc = new NewClass();
    nc.putTextNow();
}

package test1;

public class NewClass {
    public void putTextNow () {
        NewJFrame nf = new NewJFrame();
        nf.jLabel1.setText("OK!");
    }
}

public NewJFrame() {
    initComponents();
}

@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);

    jLabel1.setText("jLabel1");

    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(114, 114, 114)
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addComponent(jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, 107, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addGroup(layout.createSequentialGroup()
                    .addGap(23, 23, 23)
                    .addComponent(jButton1)))
            .addContainerGap(179, Short.MAX_VALUE))
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addGap(96, 96, 96)
            .addComponent(jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, 73, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addGap(43, 43, 43)
            .addComponent(jButton1)
            .addContainerGap(65, Short.MAX_VALUE))
    );

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

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    NewClass nc = new NewClass();
    nc.putTextNow();
}                                        

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

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

//newclass.java

    package test1;

public class NewClass{public void putTextNow（）{
NewJFrame nf=new NewJFrame（）；nf.jlabel1.settext（“ok”）；}}

Answer 1

NewJFrame nf = new NewJFrame();
nf.jLabel1.setText("OK!");

在NewClass类中，您正在创建NewJFrame的新实例。您正在尝试更新一个不在当前JFrame中的标签（您所看到的那个）。您必须从newjframe传递对jlabel的引用，并从那里进行更新：

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
    NewClass nc = new NewClass();
    nc.putTextNow(myJLabel);
}

newclass变为

public class NewClass {
    public void putTextNow (JLabel label) {
        label.setText("OK!");
    }
}