Java - If statement in foreach not called - if-statement

Question

I am trying to check if a certain string is in a collection of strings. (The strings in this case are Topics from a activemq broker) So basically I iterate through a topic list and compare those topics with the searched one (save in variable "compare"). "topic.getTopicName()" definately returns a string so I do not get why the varaible count is not set to 1 eventhough the condition is true in one case. So the statement in the IF clause is never executed. Am I overlooking something?
public ArrayList<String> getTopics() throws RemoteException {
try {
// get Topics as Strings from Broker
ActiveMQConnectionFactory connectionFactory = new ActiveMQConnectionFactory("tcp://localhost:61616");
ActiveMQConnection connection;
connection = (ActiveMQConnection) connectionFactory.createConnection();
connection.start();
DestinationSource ds = connection.getDestinationSource();
Set<ActiveMQTopic> topics = ds.getTopics();
String compare = "Physical";
int count = 0;
for(ActiveMQTopic topic : topics){
System.out.println(topic.getTopicName());
if(compare == topic.getTopicName()) {
System.out.println("Found " + topic.getTopicName());
count = count + 1;
}
}
if(count == 0){
System.out.println("No topic found");
}
else System.out.println("Topic found");
} catch (JMSException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}

Answer 1

I can't fully debug your code because I'm not sure what is in ActiveMQConnectionFactory but I can provide some advice.
Try adding
if(compare == topic.getTopicName()) {
System.out.println("Found " + topic.getTopicName());
count = count + 1;
}
else {
System.out.println("Not Found " + topic.getTopicName());
}
The following else statement so you can see what happens when they should be equal. Additionally, I think you should be comparing string using .equals() not == since Strings are objects.
You can see string comparison using == fail in the following code:
public static void main(String[] args) {
String compare = "Physical";
String someString = new String("Physical");
String[] words = {"Test", "Cheese", "Physical", someString};
for (String s: words) {
if(s == compare) {
System.out.println(s + " == " + compare);
}
else {
System.out.println(s + " " + "!= " + compare);
}
}
System.out.println("---------------------------------------");
for (String s: words) {
if(s.equals(compare)) {
System.out.println(s + " == " + compare);
}
else {
System.out.println(s + " " + "!= " + compare);
}
}
}
Prints
Test != Physical
Cheese != Physical
Physical == Physical
Physical != Physical
---------------------------------------
Test != Physical
Cheese != Physical
Physical == Physical
Physical == Physical

Answer 2

Strings cannot be compared using the == operator. Specific information can be found here : How do I compare strings in Java?
Change this line of code
if(compare == topic.getTopicName())
to this
if (compare.equals(topic.getTopicName())