谁能帮我有个问题,请帮忙!!

andyj2ee
03-01-13 4 169

banq 你好,我有个问题,请帮忙!! 发表时间: 2003年01月02日 14:32:41 回复

DatabaseObjectIterator.java 中有如下构造器我不明白。
extraObject 是Object 的类型。为什么能:ForumFactory factory = (ForumFactory)extraObject;
在DbForum 中传过来的只是this.它只实现了Forum, //public class DbForum implements Forum, Cacheable //
且我只看到有一个private DbForumFactory factory; 变量。
return new DatabaseObjectIterator(JiveGlobals.THREAD, popularThreads,this);






public DatabaseObjectIterator(int type, long [] elements,
final Object extraObject)
{
this.elements = elements;

// Load the appropriate proxy factory depending on the type of object
// that we're iterating through.
switch (type) {
// FORUM
case JiveGlobals.FORUM:
// Create an objectFactory to load forums.
this.objectFactory = new DatabaseObjectFactory() {
ForumFactory factory = (ForumFactory)extraObject;

public Object loadObject(long id) {
try {
Forum forum = factory.getForum(id);
return forum;
。。。。。。。。。。。。。。。。。。

andyj2ee
2003-01-13 01:08

我作了一个测试如下:报错啊。!!

谁能帮我看看。


class Forum{};
class ForumFactory {
public Forum getForum(long id) {
return new Forum();
}
}

interface DatabaseObjectFactory {
public Object loadObject(long id);
}

class DatabaseObjectIterator {

private DatabaseObjectFactory objectFactory;
public DatabaseObjectIterator(final Object extraObject)
{

this.objectFactory = new DatabaseObjectFactory() {
ForumFactory factory = (ForumFactory)extraObject;

public Object loadObject(long id) {
Forum forum = factory.getForum(id);
return forum;
}
};
}

}

class DBIteratorTest
{
public static void main(String[] args)
{
System.out.println("Hello World!");
DBIteratorTest db = new DBIteratorTest();

new DatabaseObjectIterator(db);
}
}



//
/*
---------- java ----------
Hello World!
java.lang.ClassCastException
at DatabaseObjectIterator$1.<init>(DBIteratorTest.java:24)
at DatabaseObjectIterator.<init>(DBIteratorTest.java:23)
at DBIteratorTest.main(DBIteratorTest.java:42)
Exception in thread "main" Normal Termination
Output completed (0 sec consumed).
*/

andyj2ee
2003-01-14 19:16

不用回答了。我明白了。

hxz
2003-01-20 11:06

到底是什么啊?
我今天看了好久啊!

hxz
2003-01-20 11:45

严重gz