Need some help to understand what is done in the second line of code?

Question

 public <T> void addToRequestQueue(Request<T> req, String tag) {
    req.setTag(TextUtils.isEmpty(tag) ? TAG : tag);
    getRequestQueue().add(req);
}

what is done in this second line? I can't understand what is this (tag) ?TAG :tag.

Here is the full code

{
import android.app.Application;
import android.text.TextUtils;

import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.toolbox.Volley;

public class AppController extends Application {

    public static final String TAG = AppController.class.getSimpleName();

    private RequestQueue mRequestQueue;

    private static AppController mInstance;

    @Override
    public void onCreate() {
        super.onCreate();
        mInstance = this;
    }

    public static synchronized AppController getInstance() {
        return mInstance;
    }

    public RequestQueue getRequestQueue() {
        if (mRequestQueue == null) {
            mRequestQueue = Volley.newRequestQueue(getApplicationContext());
        }

        return mRequestQueue;
    }

    public <T> void addToRequestQueue(Request<T> req, String tag) {
        req.setTag(TextUtils.isEmpty(tag) ? TAG : tag);
        getRequestQueue().add(req);
    }

    public <T> void addToRequestQueue(Request<T> req) {
        req.setTag(TAG);
        getRequestQueue().add(req);
    }

    public void cancelPendingRequests(Object tag) {
        if (mRequestQueue != null) {
            mRequestQueue.cancelAll(tag);
        }
    }
}

here is the full code now tell me and please explain if you can that what is done in that method second line

How will we know? It's your code. Looks like some instance variable of class Request. Please provide complete context if it is generic enough. — Aniket Thakur, Mar 26 '16 at 14:30
yes how the operator working and what the code of second line of that method done — Mian Hassan, Mar 26 '16 at 14:47
An expression "b ? v1 : v2" evaluates the boolean "b" and if it is true then the expression has value v1 else it has the value v2. Kind of like "int questionmark ( boolean b, int v1, int v2 ) { if (b) return v1; return v2; } but it's not limited to int's -- v1/v2 can be any type. — John Hascall, Mar 26 '16 at 14:53
thanks John ...thanks for such a concept really appreciate your knowledge — Mian Hassan, Mar 26 '16 at 16:15
Possible duplicate of [What is the Java ?: operator called and what does it do?](https://stackoverflow.com/questions/798545/what-is-the-java-operator-called-and-what-does-it-do) — domsson, Jul 24 '17 at 12:46

Sergey Kalinichenko · Answer 1 · 2016-03-26T15:04:41.187

0

TAG must be some constant of type String representing the default value of tag, whatever it is - something like this:

public static final String TAG = "<default-tag>";

The idea here is to tag your request with the value passed as the second parameter, i.e. String tag. Conditional operator ?: is used to implement the check without using an if/else statement.

When the tag string passed in the call to addToRequestQueue happens to be empty, the method uses the value of TAG instead.

edited Mar 26 '16 at 15:04

answered Mar 26 '16 at 14:31

Sergey Kalinichenko

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Please also add that this is the ternary or inline if operator. And a link explaining that. – Nic Mar 26 '16 at 14:53

score 0 · Answer 2 · answered Mar 26 '16 at 14:56

Translation of the second line

public static final String TAG = AppController.class.getSimpleName();

public <T> void addToRequestQueue(Request<T> req, String tag) {
    req.setTag("is tag empty?" yes, so use `TAG` : no, so use `tag`);
    getRequestQueue().add(req);
}

In another words:

if(tag.isEmpty()){
  res.setTag(TAG)

} else {
  res.setTag(tag)

}

Need some help to understand what is done in the second line of code?

2 Answers2