设置文本字段文本时出现NullPointerException

Question

有人可以帮助我,因为我必须在明天结束之前完成这个项目吗？

每次我尝试设置文本字段的文本时,程序崩溃并给出空指针异常.我怎么能克服这个？

以下是发生错误的示例代码:

package disciplinesys;

public class NewJFrame extends javax.swing.JFrame {

    /** Creates new form NewJFrame */
    public NewJFrame() {
        jTextField1.setText("Yes");
        initComponents();
    }

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

        jTextField1 = new javax.swing.JTextField();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        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(120, 120, 120)
                .addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, 139, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(141, Short.MAX_VALUE))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(116, 116, 116)
                .addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(164, Short.MAX_VALUE))
        );

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

    /**
    * @param args the command line arguments
    */
    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new NewJFrame().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify
    private javax.swing.JTextField jTextField1;
    // End of variables declaration

}

Answer 1

jTextField1.setText("Yes");之后打电话initComponents();

像这样:

/** Creates new form NewJFrame */
public NewJFrame() {
    initComponents();
    jTextField1.setText("Yes");
}

这是因为你的textfield变量在创建之前不会被创建 initComponents();