Develop Reference

Where is the R.java file in Android Studio?

Where is the R.java file in Android Studio? Can someone please help with this? I already tried google for the answer but can't find any solution.

Based on the new stable release of Android Studio (3.6) we have:
So, now to find your generated resource classes you need the following steps:
1) Open your project.
2) Go to your module build path.
3) Open the outputs/apk/debug/app-name-debug.apk file.
4) Choose your classes.dex file.
5) Look at the down placed area and go to your full package path.
6) You can see all bytecoded resource classes. So, scroll down to what you are looking for.
7) Expand the resource class you need to proceed (for example, let it be R.id)
8) Go to you id's.
That's it.
UPDATE:
If you would like to see actual id integer number you should follows steps below:
1) By (7) Go to the resource class you need to proceed and right click to show the context menu
2) Choose "Show Bytecode" to see the flexible dialog "DEX Byte Code for R$id", for example, for id class
3) Scroll down to the actual id to look its number

Although the current Android Gradle Plugin doesn't generate a R.java anymore you can still inspect the corresponding class file (see Sergey V.`s answer).
However, if you (like probably in most cases) just want to look up the generated IDs for your resources, there is an easier way:
In the project pane on the left hand side switch from Android to Project view using the drop-down at the top. Then navigate to app/build/intermediates/runtime_symbol_list/<insert build type here>/R.txt. This file lists all IDs generated by AGP during the build process.

I use Android Studio 3.3.2
\app\build\generated\not_namespaced_r_class_sources\debug\processDebugResources\r\android\support\constraint\R.java

As noted above, "The new Android Gradle Plugin generates the corresponding bytecode directly and does not make the intermediate R.java file".
Using the ubuntudroid solution you can find an id also this way. Find R.txt and copy absolute path. Project > app > build > intermediates > runtime_symbol_list > debug > R.txt. Then right click and select Copy Path..., 1. Absolute Path Ctrl+Shift+C.
This way you will obtain a path to R.txt, for instance, "C:\Users\user\AndroidStudioProjects\your_project\app\build\intermediates\runtime_symbol_list\debug\R.txt". Copy the path without R.txt to a text file for future references, for example, with Notepad++.
Press Ctrl+Shift+F to find in directory. Insert an id and the path.
== Old answer ==
Change a project view from Android to Project or Project Files. Find one of these two files.
Then you can revert back to Android view.

I use Android Studio 2.3.3. The R.java file is shown in the picture above.
In the left upper side, there is a select list. Select the [project] option so that you can see all the folders and files.

R.java is the generated file by ADT or Android studio. It will be located under app\build\generated\source\r directory.
./app/build/generated/source/r/debug/android/support/v7/appcompat/R.java
./app/build/generated/source/r/debug/your/packagename/name/R.java

I am using Android Studio 2.2.3 , the R.java file is shown in the picture below.
Goto in the left upper side there is a selecting list ,
select [package]
Open "App Folder"
com.example.saeedanwar.myapplication;
r

In my project in Android Studio 4.1
R.jar that you can actually unzip resides in app build folder, as follows:
jar -xf R.jar
Once the jar is unpacked you can find R.java inside of app package:

If you're using Mac or Linux, try the following command line on your terminal:
find . -name "R.*"
It will print something like:
./app/build/intermediaries/runtime_symbol_list/debug/R.txt
./app/build/intermediaries/compile_and_runtime_not_namespaced_r_class_jar/debug/R.jar

It is inside app\build\generated\source\r folder

Project/app/build/generated/source/r/debug/com.android.'projectname'/R.java

--The R.Java that contains your xml layouts and views id's in Android Studio 3.5.3 -- Project/app/build/generated/not_namespaced_r_class_sources/debug/r/com/"your package"/R.java

This answer will be in a constant state of flux until Android standardize a method of matching their annoying decimal/hexadecimal id references to a tangible resource such as my_layout.xml.
For Android Studio Dolphin | 2021.3.1 Patch 1 have a look at this file:
/project/package/build/intermediates/stable_resource_ids_file/debug/stableIds.txt
It is produced by RUN (not just BUILD). Sample:
layout/mtrl_picker_header_fullscreen = 0x7f0d00de
string/cancel = 0x7f1101f0
style/ThemeOverlay.MaterialComponents.MaterialCalendar = 0x7f1202f3
id/gpxBtn = 0x7f0a0346

Java encoding with Eclipse and Maven

I have often seen problems arise with encoding. Therefore I have written down this instruction set to do all the needed actions in order to make things work (with encoding).
This set is related to Eclipse but it will also guide with maven settings.
The issue with encoding is most problematic when using scandinavian letters in java files (åäö, and they had actual meaning on runtime).
An example case is having a constant variable in a java file, that contains a scandic letter and it is used to identify a value from incoming stream (wich is in UTF-8).
Also the underlying OS may be Windows and they use cp1252 by default.
E.g. the following code:
#Test
public void scandicTest() {
System.out.println("scandics: åäö");
}
When everything is configured correctly (e.g. in eclipse), running this test will produce:
scandics: åäö
But if you run this via Maven (from command line or in eclipse => mvn test), you will have:
scandics: ���
First of all, the encoding needs to be changed in eclipse and also in the maven pom.xml to read and store files correctly and for the eclipse to use correct encoding when saving the files / running tests.
However the constant value in the java file itself remains corrupted even that the files read in are correct (containing the scandic letters) when the Maven and the resulting java code handled the incoming streams (compiled & run the tests).
The System Java still uses a OS specific default encoding even that everything else is set correctly. For this reason you can not configure all within the project, you must do it for the OS-JVM also.

I will explain all the the encoding steps needed for this, even that there are multiple answers for this "common" part already (at least for step 2). My particular case is to resolve step 3.
Configure the eclipse:
Open: Window > Preferences
Type 'encoding' in the search field
There will be lots of entries, but first select the 'General > Workspace'
Find the 'Text file encoding' and select: Other > UTF-8
You also want/need to set the encoding also for all the 'General > Content Types'
Select 'text' item from the right hand panel (will open a list of file types), and browse through all the types. Set their 'Default encoding' to 'UTF-8'
Click the 'update' button to persist the change.
You may need to do this also for all the other entries and items found with the search.
E.g. 'Web > CSS Files > Encoding' | ISO 10646/Unicode(UTF-8)
When all set, the Eclipse should behave properly with the encoding.
Set the encoding in maven.pom.xml
<project>
...
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
</properties>
...
</project>
You may need to set the encoding for all plugins also.
<plugin>
...
<configuration>
<encoding>UTF-8</encoding>
...
</configuration>
</plugin>
or
<plugin>
<executions>
<execution>
<configuration>
<encoding>UTF-8</encoding>
...
</configuration>
...
</execution>
</executions>
</plugin>
Though i am not sure if the latter is mandatory or if it will take the default actually.
Configure the OS
You need to set environment variable JAVA_TOOL_OPTIONS with value -Dfile.encoding=UTF8
As suggested in comment, here's some more info for converting a file:
You should note that all the files must have the UTF-8 encoding in order them to work. If you edit everything via eclipse with the given configuration, they will be as UTF-8.
If you receive a file that you should process with your code, you may need to convert that. You can simply do that by opening it in eclipse and saving the file again (you may need to add and remove a character to enable saving).
If you can use NotePad++, there is an 'encoding' menu for converting the file.
When converting a file, the scandics may get corrupted sometimes, so you need to check them manually after conversion.
And one more thing. The files saved in other tools, may have the BOM. (Byte Order Mark). This 'character' is invisible and for example an XML file containing this can not be read in by some parsers.
You can remove the BOM mark by opening the file in eclipse and setting the cursor before the first character in the file, then tab once the 'backspace'. Nothing changes, but the character gets actually removed and the file works then.
NotePad may insert the BOM-mark, so do not use it for editing XML files!

Matlab doesn't see .jar file

Ok, I'm stumped here. I'm using Matlab version 2013b with a Java RTE of 1.7.0_11 and I'm trying to run a simple piece of code to see if Matlab is able to read the .jar file and nothing seems to be working.
Here is the Java code, which is compiled to a .jar named JavaOCT.jar, which is placed in the Matlab working directory:
package VTK;
public class vtkVolumeView{
public int Test(){
return 10;
}
}
That is it, no other dependencies, nothing fancy. In Matlab, I try:
javaaddpath('\JavaOCT.jar'); %<-Directory and name are 100% correct
import VTK.*; %<-Package name from above
methodsview VTK.vtkVolumeView; %<-Can't find the class, argh!
Matlab kicks back that it can't find the class.
Things I've done to try and solve the problem:
Reverted to the exact same JDK as the Matlab RTE
Tried an older 1.6 JDK
Done lots of stack overflow research to try and solve it 1 2 3 4
Tried used javaclasspath and pointing to the compiled class instead
Read the Matlab documentation 5
Using clear -java after the javaaddpath
Any help would be appreciated, it is driving me nuts!
Update: Daniel R suggested just javaaddpath('JavaOCT.jar') which doesn't work either.
Final update: It finally works! I wasn't building the .jar properly. In IntelliJ, click on the project and hit F4. This brings up the Project Structure, then go to Artifacts and click the green + button and add DirectoryContent and then point to the out\production. Once this is done, as mentioned by others, it should show up in Matlab as an expandable .jar.

I don't know which operating system you are using, but the ./ seems invalid.
Try javaaddpath('JavaOCT.jar'); or javaaddpath(fullfile(pwd,'JavaOCT.jar'));.
What does exist(fullfile(pwd,'JavaOCT.jar')) return?

Some things to try:
Add the class file. When using a package, you need to add the class file in at the host of the package. For example, if your code is here:
\\full\path\to\code\VTK\vtkVolumeView.class
Then use:
javaaddpath('\\full\path\to\code')
I'm still suspicious of your *.jar path. You should usually use absolute paths when adding jar files. Try adding the results of which('JavaOCT.jar')
How did you make your jar file? Does it contain the appropriate directory structure implied by your package declaration?

Error: Selection does not contain a main type

I am trying to run some java files in a new project. So I make the project, put the files in it and I try to run the main file so my game starts.
I get an error that says selection does not contain a main type.
I have tried several ways to run it:
Some say to launch eclipse again, tried this a dozen times.
Somewhere else someone pointed to open a new project and make a build path to the old project.
Didn't work either.
I am pretty sure it must work because I ran it a few hours ago at school. How do I get this working? Thank you in advance!

Right click on the folder where you put your main class then click on Build Path --> Use as Source Folder.
Finally run your main file as java application. Hope this problem will be solved.
If the option 'Use as Source Folder' is not visible then inside the 'Build Path' select the option 'Remove from Build Path'. This will allow 'Use as Source Folder' option to appear in the 'Build Path'.

The other answers are all valid, however, if you are still having a problem you might not have your class inside the src folder in which case Eclipse may not see it as part of the project. This would also invoke the same error message you have seen.

I hope you are trying to run the main class in this way, see screenshot:
If not, then try this way. If yes, then please make sure that your class you are trying to run has a main method, that is, the same method definition as below:
public static void main(String[] args) {
// some code here
}
I hope this will help you.

The entry point for Java programs is the method:
public static void main(String[] args) {
//Code
}
If you do not have this, your program will not run.

I resolved this by adding a new source folder and putting my java file inside that folder. "source folder" is not just any folder i believe. its some special folder type for java/eclipse and can be added in eclipse by right-click on project -> properties -> Java buld path -> Source and add a folder

Few things to check out:
Do you have a main package? do all of your classes are under this package?
Do you use a main class with public static void main(String[] args)?
Do you declare: package ; in your main class?
You can always clean the project before running it. In Eclipse - Just go to Project -> clean then run the app again.

I ran into the same problem. I fixed by right click on the package -> properties -> Java Build Path -> Add folder (select the folder your code reside in).

I am running eclipse from Ubuntu. Had this same problem and was able run the program through terminal. So I just moved the existing public static void main(String[] args) { just below the class declaration (it got automatically formatted by eclipse) and the next launch was successful. Then moved the main method back to where it was before and it worked fine this time.

I had this problem in two projects. Maven and command line worked as expected for both. The problems were Eclipse specific. Two different solutions:
Project 1): Move the main method declaration to the top within the class, above all other declarations like fields and constructors. Crazy, but it worked.
Project 2): The solution for Project 1) did not remedy the problem. However, removing lombok imports and explicitly writing a getter method solved the problem
Conclusion:
Eclipse and/or the lombok plugin have/has a bug.

Looks too late to answer but might help someone,
Having same problem i solved it by following steps:::::
Select Main class in eclipse then click on Window in menu bar,
Window-->Show view-->Select Outline
Right click on main(String[]):void then Run As --> java Application
By doing this you can run the main method directly. This worked for me

Right Click > Run AS > Run Configurations
In this screen if your "Main class" Text field is empty, then add the class name by clicking "Search" button on the right side of the text field and choose the class file. And then click "Run" button on the bottom of the configuration screen. That's it

You must place all your files (file.java) under the root folder SRC.

Make sure the main in public static void main(String[] args) is lower case. For me it didn't work when I had it with capital letter.

Put your Main Java class file in src/main/java folder and check if there is not any error in 'Java Build Path' by following right click on project and select Java Build Path->Source.

If you are working with a Maven project you have to understand the fact that directory layout is bit different. In this the package name must be src/main/java.
For this update your source folder by right click on project root folder -> properties -> java build path -> source tab. Here remove all other source folders as they might have been added in wrong manner. Now, select project /src/main/java as the source folder. Add and apply the changes. Now refresh your workspace using F5.
This should fix the issue of not recognizing a main type.

I ran into the same issue and found that there was an extra pair of braces (curly brackets) enclosing public static void main(String args) { ... }. This method should really be at the top scope in the class and should not be enclosed around braces. It seems that it is possible to end up with braces around this method when working in Eclipse. This could be just one way you can see this issue when working with Eclipse. Happy coding!

I had this happen repeatedly after adding images to a project in Eclipse and making them part of the build path. The solution was to right-click on the class containing the main method, and then choose Run As -> Java Application. It seems that when you add a file to the build path, Eclipse automatically assumes that file is where the main method is. By going through the Run As menu instead of just clicking the green Run As button, it allows you to specify the correct entry-point.

When you save your file, make sure it has the extension .java. If it does not, Eclipse won't know to read it as a java file.

I had this issue because the tutorial code I was trying to run wasn't in the correct package even though I had typed in the package name at the top of each class.
I right-clicked each class, Refactor and Move To and accepted the package name suggestion.
Then as usual, Run As... Java Application.
And it worked :)

You must check this as well, Go to Java build path -> config build path, check that JRE System Library [Java SE -version] is check marked, try running the code again. This fixed my issue.

In my case I was using ant to perform the build, and clearly had the class setup in the build.xml file:
<target name="jar">
<jar destfile="ec-stats.jar" includes="bin/**,src/**">
<manifest>
<attribute name="Main-Class" value="my.package.MyStatistics" />
</manifest>
</jar>
</target>
But it still kept giving me the same error, until I right-clicked on the folder in Eclipse and chose Build Path -> Use As Source Folder.
See also Error: Selection does not contain a main type

Solved the issue as following:
Going in Properties of the Project
1.1) Inside "Java Compiler": chose the: "Compiler compliance level:" to a specific version of JDK (in my case I choosed 15)
1.2) Inside "Java Build Path", in the tab "Libraries", at the Modulepath: change the "JRE System Library" to the same of the version you choosed at step 1.1 above (in my case I picked JDK 15)
Run the java file that contains a main method

This can be resolved in two steps if you are using Eclipse IDE.
👉 Step I: Right click on the project and click Maven > Choose Up-date Project
👉 Step II: Select the project the click Ok button
Hope this helps.✔

This error usually occurs because jdk is not selected for the project. I had the same problem and this worked for me.
Make sure that your class file is inside src folder then follow below steps
Step 1: Right click on project folder
Step 2: Build Path --> Configure Build Path
Step 3: Select "Java Build Path" from the left corner of the window
Step 4: Under "Order and Export" Tab
Step 5: Click on any of the jdk available check box to select it.
Step 6: Click on Apply and Close.

Where are all the standard Android icon resources?

I have just started writing my first ever Java/Android application, so forgive the total n00b question.
How do you access the the standard operating system icons such as search icon/menu icon etc? They are not in the res/drawable folder where I would expect to find them. Are they available as part of the SDK or must you download them seperately?
EDIT
Maybe you can help me further - I am getting the following error (repeated on):
[2011-09-08 19:59:47 - TweetTab] C:\Users\Dan\workspace\TweetTab\res\menu\options_menu.xml:4: error: Error: No resource found that matches the given name (at 'icon' with value '#drawable/ic_menu_search').
However, the icon is not empty, the xml looks like this:
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
<item android:id="#+id/search"
android:icon="#drawable/ic_menu_search"
android:title="#string/search"/>
</menu>
Am I missing something?
SOLVED
I changed android:icon="#drawable/ic_menu_search" to android:icon="#android:drawable/ic_menu_search" and it could then find the icon.

You can acces them via android.R.drawable.* or in xml by #android:drawable/something.

I installed the Android SDK for Eclipse on Windows.
Now I can find all ressources under "C:\Program Files\Android\android-sdk-windows\platforms\android-9\data\res..."

try this instead:
android:src="#android:drawable/ic_menu_camera"

it is now possible to use vector assets to generate standard (or customised) icons for android.
Add 'com.android.tools.build:gradle:1.4.0-beta3' to your build.gradle file. (The stable version will be out in the coming weeks).
Add a vector asset by right-clicking res/drawable/ > New > Vector Asset. Android Studio provides a built-in viewer for you to pick your drawable.
Reference your icon like you usually do. Eg: android:icon="#drawable/ic_help_24dp"

A lot of them can be found in android.R.drawable but not all are publicly accessible

You can find the android.R.drawable images in your local SDK folder. (Tested using Android Studio 3.0)
First have a look at the docs for the names of the drawables here: https://developer.android.com/reference/android/R.drawable.html
Second either search your drive for one of those image names.png or type in the name of any of them into your Android Studio activity and right click (goto declaration) on it to view the image. Then you can also right click that image to copy the path. Then open that folder and look at all the PNG's there.
Example on windows 10: android.R.drawable.star_big_on is located in user/AppData/Local/Android/Sdk/platforms/android-25/data/res/drawable-hdpi/star_big_on.png
(Note also on windows AppData is a hidden folder so you may need to set your windows explorer to show hidden if you are clicking to open each folder)
Also if you need to see material design icons / descriptions this is a good place to look: https://material.io/icons

Someone may see this page useful for getting those icons... http://developer.android.com/design/style/iconography.html

For those of you in the Visual Studio/Xamarin Android camp, you can view and add the standard Material icons pretty easily using the following plugin:
https://marketplace.visualstudio.com/items?itemName=nikainteristi.Materialiconsgenerator
I've used it a few times in my projects.