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: (...)