Observablevalue check for new and old values equally - javafx

Question

In fact I have a class that performs the job of collecting website post URL.The url article I get when analyzing each page site
+http://dantri.com.vn/xa-hoi.htm
+http://dantri.com.vn/xa-hoi/trang-2.htm
....
+http://dantri.com.vn/xa-hoi/trang-9998.htm
+http://dantri.com.vn/xa-hoi/trang-n.htm
to the Property url is as follows.
public class Pagination {
private final StringProperty postURL = new SimpleStringProperty();
public String getPostURL() {
return postURL.get();
}
public void setPostURL(String value) {
postURL.set(value);
}
public StringProperty postURLProperty() {
return postURL;
}
public void gather() {
for (int i = 0; i < n; i++) {
for (String url : getAllURLToPage("http://dantri.com.vn/xa-hoi/trang-"+i+".htm")) {
setPostURL(url);
}
}
}
}
From page http://dantri.com.vn/xa-hoi/trang-9998.htm===->http://dantri.com.vn/xa-hoi/trang-n.htm.
The post url value is constant, so I want to terminate the program when consecutive url are equal,eg newValue.equals(oldValue) as below
public static void main(String[] args) {
Pagination pagination = new Pagination();
pagination.postURLProperty().addListener(new ChangeListener<String>() {
#Override
public void changed(ObservableValue<? extends String> observable, String oldValue, String newValue) {
if (newValue.equals(oldValue)) {
System.out.println("BREAK");
}
}
});
pagination.gather();
}
That's just the example by newValue and oldValue are always not equal with observableValue.
I hope you help me solve my problem how can i control post url i get

Answer 1

As I noted in the comment, a ChangeListener is invoked in response to a change in a property. If you call postURL.set(...) and pass the same value that is currently held in postURL, the change listener will not be invoked. (TBH it's not really clear what the purpose of the property is here.)
You could just do this in the for loop directly:
public void gather() {
for (int i = 0; i < n; i++) {
for (String url : getAllURLToPage("http://dantri.com.vn/xa-hoi/trang-"+i+".htm")) {
if (Objects.equals(url, getPostURL())) {
System.out.println("BREAK");
}
setPostURL(url);
}
}
}
or perhaps in the set method, assuming you don't call postURL.set(...) anywhere else:
public void setPostURL(String value) {
if (Objects.equals(value, postURL.get())) {
System.out.println("BREAK");
}
postURL.set(value);
}
But there is no way for a ChangeListener to detect a lack of a change.