帮忙看一下这些代码有问题啊

最近在学GWT，因为要用到一个包，所以接触到这个例子但有些不明白，这些代码是

[code="java"]package com.google.code.gwt.database.sample.hellodatabase.client;

import java.util.Date;
import java.util.List;

import com.google.code.gwt.database.client.Database;
import com.google.code.gwt.database.client.service.DataServiceException;
import com.google.code.gwt.database.client.service.ListCallback;
import com.google.code.gwt.database.client.service.RowIdListCallback;
import com.google.code.gwt.database.client.service.ScalarCallback;
import com.google.code.gwt.database.client.service.VoidCallback;
import com.google.gwt.core.client.EntryPoint;
import com.google.gwt.core.client.GWT;
import com.google.gwt.event.dom.client.ClickEvent;
import com.google.gwt.event.dom.client.ClickHandler;
import com.google.gwt.user.client.Window;
import com.google.gwt.user.client.ui.Button;
import com.google.gwt.user.client.ui.DialogBox;
import com.google.gwt.user.client.ui.Image;
import com.google.gwt.user.client.ui.Label;
import com.google.gwt.user.client.ui.RootPanel;
import com.google.gwt.user.client.ui.VerticalPanel;

/**

Entry point classes define onModuleLoad().
*/
public class HelloDatabase implements EntryPoint {
ClickCountDataService dbService = GWT.create(ClickCountDataService.class);
private VerticalPanel vPanel;
/**
- This is the entry point method. */ public void onModuleLoad() { if (!Database.isSupported()) { Window.alert("HTML 5 Database is NOT supported in this browser!"); return; }
// Create the dialog box
final DialogBox dialogBox = new DialogBox();
dialogBox.setText("Welcome to GWT Database Demo!");
dialogBox.setAnimationEnabled(true);
Button closeButton = new Button("close", new ClickHandler() {
public void onClick(ClickEvent event) {
dialogBox.hide();
}
});
VerticalPanel dialogVPanel = new VerticalPanel();
dialogVPanel.setWidth("100%");
dialogVPanel.setHorizontalAlignment(VerticalPanel.ALIGN_CENTER);
final VerticalPanel clickedData = new VerticalPanel();
dialogVPanel.add(clickedData);
dialogVPanel.add(closeButton);
dialogBox.setWidget(dialogVPanel);
Image img = new Image("http://code.google.com/webtoolkit/logo-185x175.png");
Button addClickButton = new Button("Add Click", new ClickHandler() {
public void onClick(ClickEvent event) {
dbService.insertClick(new Date(), new RowIdListCallback() {
public void onFailure(DataServiceException error) {
Window.alert("Failed to add click! " + error);
}
```
  public void onSuccess(final List<Integer> rowIds) {
    dbService.getClicks(new ListCallback<ClickRow>() {
      public void onFailure(DataServiceException error) {
        Window.alert("Failed to query clicks! " + error);
      }

      public void onSuccess(List<ClickRow> result) {
        clickedData.clear();
        clickedData.add(new Label("Last click insert ID: "
            + rowIds.get(0)));
        for (ClickRow row : result) {
          clickedData.add(new Label("Clicked on " + row.getClicked()));
        }
        dialogBox.center();
        dialogBox.show();
      }
    });
  }
});
```
}
});
Button getCountButton = new Button("Get Counts", new ClickHandler() {
public void onClick(ClickEvent event) {
getCount();
}
});
vPanel = new VerticalPanel();
// We can add style names.
vPanel.addStyleName("widePanel");
vPanel.setHorizontalAlignment(VerticalPanel.ALIGN_CENTER);
vPanel.add(img);
vPanel.add(addClickButton);
vPanel.add(getCountButton);
// Add image and button to the RootPanel
RootPanel.get().add(vPanel);
// Create table 'clickcount' if it doesn't exist already:
dbService.initTable(new VoidCallback() {
public void onFailure(DataServiceException error) {
Window.alert("Failed to initialize table! " + error);
}
public void onSuccess() {
Window.alert("Database initialized successfully.");
getCount();
}
});
getVersion();
}
private void getVersion() {
dbService.getSqliteVersion(new ScalarCallback() {
public void onFailure(DataServiceException error) {
Window.alert("Failed to get SQLite version! " + error);
}
public void onSuccess(String result) {
vPanel.add(new Label("SQLite version: " + result));
}
});
}
private void getCount() {
dbService.getClickCount(new ScalarCallback() {
public void onFailure(DataServiceException error) {
Window.alert("Failed to get count! " + error);
}
public void onSuccess(Integer result) {
vPanel.add(new Label("There are " + result + " recorded clicks."));
}
});
}
}
[/code]

[code="java"]package com.google.code.gwt.database.sample.hellodatabase.client;

import java.util.Date;

import com.google.code.gwt.database.client.service.Connection;
import com.google.code.gwt.database.client.service.DataService;
import com.google.code.gwt.database.client.service.ListCallback;
import com.google.code.gwt.database.client.service.RowIdListCallback;
import com.google.code.gwt.database.client.service.ScalarCallback;
import com.google.code.gwt.database.client.service.Select;
import com.google.code.gwt.database.client.service.Update;
import com.google.code.gwt.database.client.service.VoidCallback;

/**

Demo database service to the 'ClckCnt' database.
@author bguijt
*/
@Connection(name="ClckCnt", version="1.0",
description="Click Counter", maxsize=10000)
public interface ClickCountDataService extends DataService {
/**
- Makes sure that the 'clickcount' table exists in the Database. */ @Update("CREATE TABLE IF NOT EXISTS clickcount ("
  - "id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, "
  - "clicked INTEGER)") void initTable(VoidCallback callback);
/**
- Records a Click value, and obtains the ID of the inserted record. */ @Update("INSERT INTO clickcount (clicked) VALUES ({when.getTime()})") void insertClick(Date when, RowIdListCallback callback);
/**
- Returns all clicks. */ @Select("SELECT clicked FROM clickcount") void getClicks(ListCallback callback);
/**
- Obtains the number of clicks recorded in the database. / @Select("SELECT count() FROM clickcount") void getClickCount(ScalarCallback callback);
/**
- Obtains the version number of the SQLite database. */ @Select("SELECT sqlite_version()") void getSqliteVersion(ScalarCallback callback); } [/code]

[code="java"]
package com.google.code.gwt.database.sample.hellodatabase.client;

import java.util.Date;

import com.google.gwt.core.client.JavaScriptObject;

/**

@author bguijt
*/
public class ClickRow extends JavaScriptObject {
protected ClickRow() {}
/**
- @return the 'clicked' property (an integer) as a Java Date (SQLite does not support DATE types). / public final native Date getClicked() /-{ var dateClicked = new Date(); dateClicked.setTime(this.clicked); return dateClicked; }-*/; } [/code]

1.请问HelloDatabase类里边的
[code="java"]
Button addClickButton = new Button("Add Click", new ClickHandler() {
public void onClick(ClickEvent event) {
dbService.insertClick(new Date(), new RowIdListCallback() {
public void onFailure(DataServiceException error) {
Window.alert("Failed to add click! " + error);
}

      public void onSuccess(final List<Integer> rowIds) {
        dbService.getClicks(new ListCallback<ClickRow>() {
          public void onFailure(DataServiceException error) {
            Window.alert("Failed to query clicks! " + error);
          }

          public void onSuccess(List<ClickRow> result) {
            clickedData.clear();
            clickedData.add(new Label("Last click insert ID: "
                + rowIds.get(0)));
            for (ClickRow row : result) {
              clickedData.add(new Label("Clicked on " + row.getClicked()));
            }
            dialogBox.center();
            dialogBox.show();
          }
        });
      }
    });
  }
});[/code]

为什么有两个onSuccess方法，而且dbService.insertClick(new Date(), new RowIdListCallback() {。。。}）里边的参数都初始化了些什么参数啊。

2.HelloDatabase 类中那个GWT.create()作用是什么，最后生成的是什么对象呢（怎么被初始化的）。
3.ClickCountDataService 里的那些注释怎么起作用的呢？

纠结中，求解啊，，

1.问题一：dbService.insertClick(new Date(), new RowIdListCallback() {。。。}）
这个是java里面的匿名函数，没猜错的话是重写了RowIdListCallback其中方法。
这种方法可以用内部类来代替。
即：
[code="java"]
private class RowIdListCallback{
public void onFailure(DataServiceException error) {

Window.alert("Failed to add click! " + error);

}

  public void onSuccess(final List<Integer> rowIds) {   
    dbService.getClicks(new ListCallback<ClickRow>() {   
      public void onFailure(DataServiceException error) {   
        Window.alert("Failed to query clicks! " + error);   
      }   

      public void onSuccess(List<ClickRow> result) {   
        clickedData.clear();   
        clickedData.add(new Label("Last click insert ID: "  
            + rowIds.get(0)));   
        for (ClickRow row : result) {   
          clickedData.add(new Label("Clicked on " + row.getClicked()));   
        }   
        dialogBox.center();   
        dialogBox.show();   
      }

}
[/code]
在使用时：
[code="java"]
dbService.insertClick(new Date(), new RowIdListCallback());
[/code]

2.
[code="java"]
ClickCountDataService dbService = GWT.create(ClickCountDataService.class);

[/code]
这句话创建的是一个服务（service），实际是ClickCountDataService实现类的一个远程对象，在服务器端。用来持久化数据。鼠标选中ClickCountDataService然后Ctrl+T就能看到具体实现

3.ClickCountDataService 里的那些注释怎么起作用的呢？
那里的注释其实不是一般的注释而是java中的“元数据”。元数据的起作用是利用了java反射机制的到Method里面有个getAnnotation方法。