我有一个类，它创建一个包含textarea和其他元素的图形界面。为了创建GUI，我使用了NetBeans，因此存在一些不可编辑的代码。 我的问题是我无法更改textarea中的文本。我尝试使用 setText（）和 append（），但textarea不会改变。问题在哪里？
public class Cifra extends javax.swing.JFrame {
/** Creates new form Cifra */
public Cifra() {
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() {
comboBox = new javax.swing.JComboBox();
jLabel1 = new javax.swing.JLabel();
chiaveField = new javax.swing.JTextField();
jScrollPane1 = new javax.swing.JScrollPane();
antMexCif = new javax.swing.JTextArea();
jScrollPane2 = new javax.swing.JScrollPane();
antMex = new javax.swing.JTextArea();
jLabel2 = new javax.swing.JLabel();
jLabel3 = new javax.swing.JLabel();
logoutButton = new javax.swing.JButton();
inviaPropostaButton = new javax.swing.JButton();
indietroButton = new javax.swing.JButton();
cifra = new javax.swing.JButton();
setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
setTitle("Cifra");
comboBox.setModel(new javax.swing.DefaultComboBoxModel(new String[] { "Scegli cifratura...", "Cesare", "Pseudocasuale", "Chiave" }));
comboBox.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
comboBoxActionPerformed(evt);
}
});
jLabel1.setText("Inserisci una chiave:");
chiaveField.setColumns(20);
antMexCif.setEditable(false);
antMexCif.setColumns(20);
antMexCif.setRows(5);
jScrollPane1.setViewportView(antMexCif);
antMex.setEditable(false);
antMex.setColumns(20);
antMex.setRows(5);
jScrollPane2.setViewportView(antMex);
jLabel2.setText("Anteprima messaggio originale:");
jLabel3.setText("Anteprima messaggio cifrato:");
logoutButton.setText("Logout");
logoutButton.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
logoutButtonActionPerformed(evt);
}
});
inviaPropostaButton.setText("Invia proposta");
indietroButton.setText("Indietro");
indietroButton.setToolTipText("");
indietroButton.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
indietroButtonActionPerformed(evt);
}
});
cifra.setText("Cifra");
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(28, 28, 28)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(comboBox, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addGroup(layout.createSequentialGroup()
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(jLabel2)
.addComponent(logoutButton))
.addGap(168, 168, 168))
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
.addComponent(jScrollPane2, javax.swing.GroupLayout.PREFERRED_SIZE, 311, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)))
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
.addGroup(layout.createSequentialGroup()
.addComponent(indietroButton)
.addGap(40, 40, 40)
.addComponent(cifra)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addComponent(inviaPropostaButton))
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(jLabel3)
.addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 311, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGroup(layout.createSequentialGroup()
.addComponent(jLabel1)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addComponent(chiaveField, javax.swing.GroupLayout.PREFERRED_SIZE, 131, javax.swing.GroupLayout.PREFERRED_SIZE))))))
.addGap(31, 69, Short.MAX_VALUE))
);
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addContainerGap()
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(comboBox, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(jLabel1)
.addComponent(chiaveField, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGap(9, 9, 9)
.addComponent(jLabel2))
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addComponent(jLabel3)))
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 223, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(jScrollPane2, javax.swing.GroupLayout.PREFERRED_SIZE, 223, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(inviaPropostaButton)
.addComponent(indietroButton)
.addComponent(cifra)))
.addGroup(layout.createSequentialGroup()
.addGap(24, 24, 24)
.addComponent(logoutButton)))
.addContainerGap(16, Short.MAX_VALUE))
);
setSize(new java.awt.Dimension(741, 389));
setLocationRelativeTo(null);
}// </editor-fold>
/**
* @param args the command line arguments
*/
public static void start() {
/* 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(Cifra.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (InstantiationException ex) {
java.util.logging.Logger.getLogger(Cifra.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (IllegalAccessException ex) {
java.util.logging.Logger.getLogger(Cifra.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (javax.swing.UnsupportedLookAndFeelException ex) {
java.util.logging.Logger.getLogger(Cifra.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
}
//</editor-fold>
antMex = new javax.swing.JTextArea(DBManager.messaggio.getTesto() + newline);
antMex.append("hello world" + newline);
antMex.setText("hello world");
/* Create and display the form */
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
new Cifra().setVisible(true);
}
});
}
private final static String newline = "\n";
// Variables declaration - do not modify
public static javax.swing.JTextArea antMex;
private javax.swing.JTextArea antMexCif;
private javax.swing.JTextField chiaveField;
public static javax.swing.JButton cifra;
private javax.swing.JComboBox comboBox;
private javax.swing.JButton indietroButton;
private javax.swing.JButton inviaPropostaButton;
private javax.swing.JLabel jLabel1;
private javax.swing.JLabel jLabel2;
private javax.swing.JLabel jLabel3;
private javax.swing.JScrollPane jScrollPane1;
private javax.swing.JScrollPane jScrollPane2;
private javax.swing.JButton logoutButton;
// End of variables declaration
}
谢谢！
答案 0 :(得分：3)
您的问题的关键在于您需要了解对象和变量之间的区别。
您正在创建一个新的JTextArea对象并将其放入antMex变量，然后设置该对象的文本：
// ******* here *******
antMex = new javax.swing.JTextArea(DBManager.messaggio.getTesto() + newline);
antMex.append("hello world" + newline);
antMex.setText("hello world");
理解这对创建的原始JTextArea对象完全没有影响，分配给antMex，并在创建和分配新对象之前添加到GUI中。
解决方案：不要创建新对象，而是继续调用原始引用上的方法。
// commenting out the line that creates the new JTextArea
// antMex = new javax.swing.JTextArea(DBManager.messaggio.getTesto() + newline);
antMex.append("hello world" + newline);
antMex.setText("hello world");
更好的解决方案：避免使用GUI代码生成器，直到您有更多的Swing体验。相信我，你将通过Swing和一般Java教程学到很多东西。
修改
Rod Algonquin非常重视我的建议是在你的对象创建之前做出的。相反，考虑给出Cifra公共方法，如：
public void setAntMexText(String text) {
antMex.setText(text);
}
public void appendAntMexText(String text) {
antMex.append(text);
}
并像这样称呼他们：
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
Cifra cifra = new Cifra();
cifra.setVisible(true);
cifra.setAntMexText("Hello World!" + NEW_LINE); // NEW_LINE should be all caps
cifra.appendAntMexText("Next Line");
}
});
答案 1 :(得分：1)
antMex.append("hello world" + newline);
antMex.setText("hello world");
在initComponents()语句之后，该代码应该在您的类的构造函数中。
也就是说，在创建变量之前，你无法引用变量。