我有一个名为 TopicS 的Listner类我试图从名为readMessages的gui中调用它
当我尝试使用以下方法运行类TopicS时,
private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
System.out.println("test test test");
System.out.print("you pressed" +topicCombobox.getSelectedItem());
TopicS a = new TopicS();
a.addTopicToListner(topicCombobox.getSelectedItem());
}
它给我错误说
主题中的addTopicListner(java.lang.String)无法应用于(java.lang.Object)
当我将String更改为Object时,我得到其他错误。下面包含主要方法,没有GUI就可以正常工作,但我需要将其添加到GUI。我想要做的是取值为String数组的组合框,并将该字符串放入主题(其中(t)现在是
import java.util.Hashtable;
import javax.jms.JMSException;
import javax.jms.Message;
import javax.jms.MessageListener;
import javax.jms.Session;
import javax.jms.TextMessage;
import javax.jms.Topic;
import javax.jms.TopicConnection;
import javax.jms.TopicConnectionFactory;
import javax.jms.TopicSession;
import javax.jms.TopicSubscriber;
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;
public class TopicS implements MessageListener
{
private TopicConnection topicConnection;
private TopicSession topicSession;
public Topic topic;
private TopicSubscriber topicSubscriber;
public TopicS()
{}
public void addTopicToListner(String t){
try
{
// create a JNDI context
Hashtable properties = new Hashtable();
properties.put(Context.INITIAL_CONTEXT_FACTORY,"org.exolab.jms.jndi.InitialContextFactory");
properties.put(Context.PROVIDER_URL,"rmi://localhost:1099/");
Context context = new InitialContext(properties);
// retrieve topic connection factory
TopicConnectionFactory topicConnectionFactory =
(TopicConnectionFactory)context.lookup("JmsTopicConnectionFactory");
// create a topic connection
topicConnection = topicConnectionFactory.createTopicConnection();
// create a topic session
// set transactions to false and set auto acknowledgement of receipt of messages
topicSession = topicConnection.createTopicSession(false,Session.AUTO_ACKNOWLEDGE);
// retrieve topic
topic = (Topic) context.lookup(t);
// create a topic subscriber and associate to the retrieved topic
topicSubscriber = topicSession.createSubscriber(topic);
// associate message listener
topicSubscriber.setMessageListener(this);
// start delivery of incoming messages
topicConnection.start();
}
catch (NamingException e)
{
e.printStackTrace();
}
catch (JMSException e)
{
e.printStackTrace();
}
}
/* public static void main(String[] args)
//{
try
{
TopicS listener = new TopicS();
Thread.currentThread().sleep(2000);
}
catch (InterruptedException e)
{
e.printStackTrace();
}
}
*/
// process incoming topic messages
public void onMessage(Message message)
{
try
{
String messageText = null;
if (message instanceof TextMessage)
messageText = ((TextMessage)message).getText();
System.out.println(messageText);
}
catch (JMSException e)
{
e.printStackTrace();
}
}
}
答案 0 :(得分:2)
JComboBox.getSelectedItem()
会返回Object
类型,而非String
。您可以在其结果上调用toString()
以返回对象的字符串表示形式。您好像要尝试返回Topic
类型,这意味着您需要覆盖toString()
上的Topic
方法以返回所需的值。
答案 1 :(得分:1)
那是因为JComboBox.html.getSelectedItem()返回Object
public Object getSelectedItem()
你的方法需要一个字符串
public void addTopicToListner(String t)
如果你100%确定你的组合框的内容是字符串你只需要施放它:
a.addTopicToListner( (String) topicCombobox.getSelectedItem());
就是这样。
此代码示例完全重现您的编译错误:
class StringAndObject {
public void workWithString( String s ) {} // We just care about
public void workWithObject( Object o ) {} // the signature.
public void run() {
String s = ""; // s declared as String
Object o = s; // o declared as Object
// works because a String is also an Object
workWithObject( s );
// naturally a s is and String
workWithString( s );
// works because o is an Object
workWithObject( o );
// compiler error....
workWithString( o );
}
}
输出:
StringAndObject.java:19: workWithString(java.lang.String) in StringAndObject cannot be applied to (java.lang.Object)
workWithString( o );
^
1 error
如您所见,即使 是String对象,最后一次调用(workWithString(o)
)也无法编译。事实证明,编译器只知道o
被声明为Object
,但它没有办法知道该对象是字符串还是其他东西(例如Date
)。
我希望这会有所帮助。
答案 2 :(得分:0)
尝试以下代码
topicCombobox.getSelectedItem() instanceof String ? (String)topicCombobox.getSelectedItem() : "Socks";
这是一个临时修复,因为我不知道传入的getSelectedItem()
是否为String
。
如果你知道它总是会被施展它
(String)topicCombobox.getSelectedItem()