java - Netbeans CRUD 应用程序中的错误

Question

package org.shop.ui;

import demo.Customer;
import java.util.List;
import java.util.logging.Logger;
import javax.persistence.EntityManager;
import javax.persistence.Persistence;
import javax.persistence.Query;
import org.openide.util.NbBundle;
import org.openide.windows.TopComponent;
import org.openide.windows.WindowManager;
import org.openide.util.ImageUtilities;
import org.netbeans.api.settings.ConvertAsProperties;

/**
 * Top component which displays something.
 */
@ConvertAsProperties(dtd = "-//org.shop.ui//Customer//EN",
autostore = false)
public final class CustomerTopComponent extends TopComponent {

    private static CustomerTopComponent instance;
    /** path to the icon used by the component and its open action */
    static final String ICON_PATH = "org/shop/ui/einstein_clerk.gif";
    private static final String PREFERRED_ID = "CustomerTopComponent";

    EntityManager entityManager = Persistence.createEntityManagerFactory("CustomerLibraryPU").createEntityManager();
Query query = entityManager.createQuery("SELECT c FROM Customer c");
List<Customer> resultList = query.getResultList();
for (Customer c : resultList) {
  jTextArea1.append(c.getName() + " (" + c.getCity() + ")" + "\n");
}

    public CustomerTopComponent() {
        initComponents();
        setName(NbBundle.getMessage(CustomerTopComponent.class, "CTL_CustomerTopComponent"));
        setToolTipText(NbBundle.getMessage(CustomerTopComponent.class, "HINT_CustomerTopComponent"));
        setIcon(ImageUtilities.loadImage(ICON_PATH, true));


    }

    /** 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.
     */
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        jScrollPane1 = new javax.swing.JScrollPane();
        jTextArea1 = new javax.swing.JTextArea();

        jTextArea1.setColumns(20);
        jTextArea1.setRows(5);
        jScrollPane1.setViewportView(jTextArea1);

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(this);
        this.setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addComponent(jScrollPane1, javax.swing.GroupLayout.DEFAULT_SIZE, 390, Short.MAX_VALUE)
                .addContainerGap())
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                .addComponent(jScrollPane1, javax.swing.GroupLayout.DEFAULT_SIZE, 289, Short.MAX_VALUE)
                .addContainerGap())
        );
    }// </editor-fold>                        

    // Variables declaration - do not modify                     
    private javax.swing.JScrollPane jScrollPane1;
    private javax.swing.JTextArea jTextArea1;
    // End of variables declaration                   
    /**
     * Gets default instance. Do not use directly: reserved for *.settings files only,
     * i.e. deserialization routines; otherwise you could get a non-deserialized instance.
     * To obtain the singleton instance, use {@link #findInstance}.
     */
    public static synchronized CustomerTopComponent getDefault() {
        if (instance == null) {
            instance = new CustomerTopComponent();
        }
        return instance;
    }

    /**
     * Obtain the CustomerTopComponent instance. Never call {@link #getDefault} directly!
     */
    public static synchronized CustomerTopComponent findInstance() {
        TopComponent win = WindowManager.getDefault().findTopComponent(PREFERRED_ID);
        if (win == null) {
            Logger.getLogger(CustomerTopComponent.class.getName()).warning(
                    "Cannot find " + PREFERRED_ID + " component. It will not be located properly in the window system.");
            return getDefault();
        }
        if (win instanceof CustomerTopComponent) {
            return (CustomerTopComponent) win;
        }
        Logger.getLogger(CustomerTopComponent.class.getName()).warning(
                "There seem to be multiple components with the '" + PREFERRED_ID
                + "' ID. That is a potential source of errors and unexpected behavior.");
        return getDefault();
    }

    @Override
    public int getPersistenceType() {
        return TopComponent.PERSISTENCE_ALWAYS;
    }

    @Override
    public void componentOpened() {
        // TODO add custom code on component opening
    }

    @Override
    public void componentClosed() {
        // TODO add custom code on component closing
    }

    void writeProperties(java.util.Properties p) {
        // better to version settings since initial version as advocated at
        // http://wiki.apidesign.org/wiki/PropertyFiles
        p.setProperty("version", "1.0");
        // TODO store your settings
    }

    Object readProperties(java.util.Properties p) {
        if (instance == null) {
            instance = this;
        }
        instance.readPropertiesImpl(p);
        return instance;
    }

    private void readPropertiesImpl(java.util.Properties p) {
        String version = p.getProperty("version");
        // TODO read your settings according to their version
    }

    @Override
    protected String preferredID() {
        return PREFERRED_ID;
    }

}

上面是netbeans应用程序crud应用程序 引用网站 -- http://platform.netbeans.org/tutorials/nbm-crud.html ——第四点。 编译上面的代码后，我在该行收到非法开始类型错误--"for (Customer c : resultList) { " 下一行还有另一个错误作为非法前向引用 请指导如何修复上述两个错误

Answer 1

这段代码:

EntityManager entityManager = Persistence.createEntityManagerFactory("CustomerLibraryPU").createEntityManager();
Query query = entityManager.createQuery("SELECT c FROM Customer c");
List<Customer> resultList = query.getResultList();
for (Customer c : resultList) {
  jTextArea1.append(c.getName() + " (" + c.getCity() + ")" + "\n");
}

需要在方法或构造函数中，正如教程明确指出的:

Add this to the end of the TopComponent constructor: (...)