Why doesn t System out println work in Android

Question

I want to print something in console  so that I can debug it   But for some reason  nothing prints in my Android application     How do I debug then   public class HelloWebview extends Activity       WebView webview          private static final String LOG TAG    WebViewDemo       private class HelloWebViewClient extends WebViewClient            Override         public boolean shouldOverrideUrlLoading WebView view  String url                view loadUrl url               return true                           Called when the activity is first created          Override     public void onCreate Bundle savedInstanceState            super onCreate savedInstanceState           setContentView R layout main           webview    WebView  findViewById R id webview           webview setWebViewClient new HelloWebViewClient             webview getSettings   setJavaScriptEnabled true           webview setWebChromeClient new MyWebChromeClient             webview loadUrl  http   example com                 System out println  I am here

User · Answer

There is no place on your phone that you can read the System.out.println();

Instead, if you want to see the result of something either look at your logcat/console window or make a Toast or a Snackbar (if you're on a newer device) appear on the device's screen with the message :) That's what i do when i have to check for example where it goes in a switch case code! Have fun coding! :)

User · Answer

if you really need System out println to work eg  it s called from third party library   you can simply use reflection to change out field in System class   try      Field outField   System class getDeclaredField  out        Field modifiersField   Field class getDeclaredField  accessFlags        modifiersField setAccessible true       modifiersField set outField  outField getModifiers    amp   Modifier FINAL       outField setAccessible true       outField set null  new PrintStream new RedirectLogOutputStream       catch NoSuchFieldException e       e printStackTrace      catch IllegalAccessException e       e printStackTrace         RedirectLogOutputStream class   public class RedirectLogOutputStream extends OutputStream      private String mCache        Override     public void write int b  throws IOException          if mCache    null  mCache                if   char  b       n                Log i  redirect from system out   mCache               mCache                else              mCache     char  b

User · Answer

Yes it does  If you re using the emulator  it will show in the Logcat view under the System out tag  Write something and try it in your emulator

User · Answer

Recently I noticed the same issue in Android Studio 3 3  I closed the other Android studio projects and Logcat started working  The accepted answer above is not logical at all

User · Answer

Correction  On the emulator and most devices System out println gets redirected to LogCat and printed using Log i    This may not be true on very old or custom Android versions    Original  There is no console to send the messages to so the System out println messages get lost   In the same way this happens when you run a  traditional  Java application with javaw   Instead  you can use the Android Log class   Log d  MyApp   I am here      You can then view the log either in the Logcat view in Eclipse  or by running the following command   adb logcat   It s good to get in to the habit of looking at logcat output as that is also where the Stack Traces of any uncaught Exceptions are displayed     The first Entry to every logging call is the log tag which identifies the source of the log message   This is helpful as you can filter the output of the log to show just your messages   To make sure that you re consistent with your log tag it s probably best to define it once as a static final String somewhere   Log d MyActivity LOG TAG  Application started      There are five one-letter methods in Log corresponding to the following levels    e   - Error w   - Warning i   - Information d   - Debug v   - Verbose wtf   - What a Terrible Failure   The documentation says the following about the levels      Verbose should never be compiled into an application except during development  Debug logs are compiled in but stripped at runtime  Error  warning and info logs are always kept

User · Answer

I dont having fancy IDE to use LogCat as I use a mobile IDE  I had to use various other methods and I have the classes and utilties for you to use if you need   class jav android Msg  Has a collection of static methods  A  methods for printing android TOASTS  B  methods for popping up a dialog box  Each method requires a valid Context  You can set the default context   A more ambitious way  An Android Console  You instantiate a handle to the console in your app  which fires up the console if it is installed   and you can write to the console  I recently updated the console to implement reading input from the console  Which doesnt return until the input is recieved  like a regular console  A  Download and install Android Console  get it from me  B  A java file is shipped with it jav android console IConsole   Place it at the appropriate directory  It contains the methods to operate Android Console  C  Call the constructor which completes the initialization  D  read lt   gt  and write the console  There is still work to do  Namely  since OnServiceConnected is not called immediately  You cannot use IConsole in the same function you instantiated it   Before creating Android Console  I created Console Dialog  which was a dialog operating in the same app to resemble a console  Pro  no need to wait on OnServiceConnected to use it  Con  When app crashes  you dont get the message that crashed the app    Since Android Console is a seperate app in a seperate process  if your app crashes  you definately get to see the error  Furthermore IConsole sets an uncaught exception handler in your app incase you are not keen in exception handling  It pretty much prints the stack traces and exception messages to Android Console  Finally  if Android Console crashes  it sends its stacktrace and exceptions to you and you can choose an app to read it  Actually  AndroidConsole is not required to crash  Edit Extras I noticed that my while APK Builder has no LogCat  AIDE does  Then I realized a pro of using my Android Console anyhow   Android Console is design to take up only a portion of the screen  so you can see both your app  and data emitted from your app to the console  This is not possible with AIDE  So I I want to touch the screen and see coordinates  Android Console makes this easy   Android Console is designed to pop up when you write to it   Android Console will hide when you backpress

User · Answer

I ll leave this for further visitors as for me it was something about the main thread being unable to System out println   public class LogUtil    private static String log       private static boolean started   false  public static void print String s          Start the thread unless it s already running     if  started            start                Append a String to the log     log    s     public static void println String s          Start the thread unless it s already running     if  started            start                Append a String to the log with a newline        NOTE  Change to print s     n   if you don t want it to trim the last newline      log     s endsWith   n      s    s     n       private static void start           Creates a new Thread responsible for showing the logs      Thread thread   new Thread new Runnable              Override         public void run                 while true                      Execute 100 times per second to save CPU cycles                  try                       Thread sleep 10                     catch  InterruptedException e                        e printStackTrace                                        If the log variable has any contents                    if  log isEmpty                               print it and clear the log variable for new data                      System out print log                       log                                                             thread start        started   true        Usage  LogUtil println  This is a string

User · Answer

System out println        is displayed on the Android Monitor in Android Studio

User · Answer

Of course  to see the result in logcat  you should set the Log level at least to  Info   Log level in logcat   otherwise  as it happened to me  you won t see your output

User · Answer

Use the  Log class  Output visible with LogCat

User · Answer

it is not displayed in your application    it is under your emulator s logcat

[java] Why doesn't "System.out.println" work in Android?

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