Java无法从同一类中获取静态变量的值

Question

I have a AppConstants class where I have some static variables and static methods. Variable like

public static final String BASE_URL = "http://www.somevalue.com/api/";
private static String MID_FIX_API;
public static final String API_CALL = BASE_URL + getMidFixApi() + "/" + GET_KEY(appContext, KEY_FOR_KEY);

As MID_FIX_API is private so I have its public getter/setter. When I set its value from another class by its setter method AppConstants.setMidFixApi("value"); and get its value from its getter method AppConstants.getMidFixApi(); Everything is fine till now
But
The problem comes when after the above lines I call static variable API_CALL shown in the code above that get value from the getter of the variable MID_FIX_API and return null despite of that we have passed value to it before.

This is the whole sequence of lines

AppConstants.setMidFixApi("getCategories");   // setting value
Log.e("InsideSuccess", "MID_FIX_API = " + AppConstants.getMidFixApi());  // working fine till here

Log.e("InsideSuccess", "API_URL = "+AppConstants.API_CALL);   // here I'm getting like this http://www.somevalue.com/api/null/somePostFix

Please point me what I'm doing wrong.

Answer 1

This has to to with initialisation order. When you call AppConstants.setMidFixApi("getCategories") the AppConstants class will be initialised before the value is set. Hence when the API_CALL is initialised, the MID_FIX_API is not yet assigned...

Answer 2

As already mentioned the variable API_CALL is initialized once, with the current value of MID_FIX_API which initially is null.

A work around is to create a static method ( getApiCall() ) which just computes the value which earlier was staticly initialized, which would just look as easy as this:

public static String getApiCall(){
    return BASE_URL + getMidFixApi() + "/" + GET_KEY(appContext, KEY_FOR_KEY);
}

Which then can be called in an easy manner AppConstants.getApiCall() .