`R.java` is the dynamically generated class, created during build process to dynamically identify all assets (from strings to android widgets to layouts), for usage in java classes in Android app. Note this `R.java` is Android specific (though you may be able to duplicate it for other platforms, its very convenient), so it doesn&#39;t have much to do with Java language constructs. Take a look [here][1], for more details.


  [1]: http://knowledgefolders.com/akc/display?url=displaynoteimpurl&amp;ownerUserId=satya&amp;reportId=2883

`R` is a class that contains ONLY public constants. (public static final). 

It is a generated class (by Android Plugin in Eclipse) that reflects the various values you defined in the `res` file. 

For instance, you should have something like: 

    android:id=&quot;@+id/about_button&quot;

somewhere in one of your layout/menu xml file in the project, and once you wrote that, Eclipse will generate a constant in the R file (which you can find it under `gen/PACKAGE/R.java`)

Read the [Resource guide in Android Developers][1] for more information about this. 

  [1]: http://developer.android.com/guide/topics/resources/index.html

`R` class is generated by Android tools from your resources before compiling your code. It contains assigned numeric constant for each resource that you can refer in your project. For example, you have XML resource file that contains `about_button`. If you didn&#39;t have `R` class, you would have to use a string &quot;about_button&quot; to refer to it in code. If you make a mistake in this string, you will only learn about it when you run your application. With `R` you will see the error much earlier at compile time.

`R` is structured in such a way that you can refer to resources via its inner classes. For example, `R.id` contains id constants and `R.layout` contains layout constants.  

I’m working with an existing schema that I’d rather not change.  The schema has a one-to-one relationship between tables Person and VitalStats, where Person has a primary key and VitalStats uses the same field as both its primary key and its foreign key to Person, meaning its value is the value of the corresponding PK of Person.

These records are created by external processes, and my JPA code never needs to update VitalStats.
For my object model I’d like my Person class to contain a VitalStats member, BUT:

When I try 

    @Entity
    public class Person{
        private long id;
        @Id
        public long getId(){ return id; }
    
        private VitalStats vs;
        @OneToOne(mappedBy = “person”)
        public VitalStats getVs() { return vs; }
    }
    
    @Entity
        public class VitalStats{
         private Person person;
        @OneToOne
        public Person getPerson() { return person; }
    }

I have the problem that VitalStats lacks an @Id, which doesn’t work for an @Entity.\

If I try

    @Id @OneToOne
    public Person getPerson() { return person; }

that solves the @Id problem but requires that Person be Serializable.  We’ll get back to that.

I could make VitalStats @Embeddable and connect it to Person via an @ElementCollection, but then it would have to be accessed as a collection, even though I know that there’s only one element.  Doable, but both a little bit annoying and a little bit confusing.

So what’s preventing me from just saying that Person implements Serializable?  Nothing, really, except that I like everything in my code to be there for a reason, and I can’t see any logic to this, which makes my code less readable.

In the meantime I just replaced the Person field in VitalStats with a long personId and made that VitalStats’s @Id, so now the @OneToOne works.

All of these solutions to what seems (to me) like a straightforward issue are a bit clunky, so I’m wondering whether I’m missing anything, or whether someone can at least explain to me why Person has to be Serializable.

TIA




JPA @OneToOne with Shared ID -- Can I do this Better?

Can someone explain why this works with the pointer: 

    char * str1;

    str1 = &quot;Hello1&quot;;

    str1 = &quot;new string&quot;;
    
    // but not this
    char str2 [] = &quot;hello&quot;;
    str2 = &quot;four&quot;;
    
    // or this
    char str3 [];
    str3 = &quot;hello&quot;;
    str3 = &quot;hello&quot;;

    


Why can a string be assigned to a char* pointer, but not to a char[] array?

In android, I&#39;m not sure I quite understand the `R` class. I&#39;m going through the sudoku example, and I have this snippet of code:

    switch (v.getId()) // the id of the argument passed is evaluated by switch statement
    {
        case R.id.about_button: // 
        Intent i = new Intent(this, about.class);
        startActivity(i);
        break;
        // More buttons go here (if any) ...
    }

I&#39;m brand new to Java, but from what I gather it looks like it&#39;s taking input (the touch screen being touched on the button) and evaluating the argument.  Then the case statement is setup if the about button is recognized, and a new interface screen is created and then navigated to on the phone.

Is this right?

If I got the gist of that correct, why is the deal with the &quot;R&quot;  class?  

Why is it called to recognize the ID of the button?  

I thought the super class (in this project) was the SudokuActivity class.  


Understand the R class in Android

In android, I'm not sure I quite understand the <code>R</code> class. I'm going through the sudoku example, and I have this snippet of code:
<pre><code class="hljs language-arduino">switch (v.getId()) // the id of the argument passed is evaluated by switch statement
{
 case R.id.about_button: // 
 Intent i = new Intent(this, about.class);
 startActivity(i);
 break;
 // More buttons go here (if any) ...
}
</code></pre>
I'm brand new to Java, but from what I gather it looks like it's taking input (the touch screen being touched on the button) and evaluating the argument. Then the case statement is setup if the about button is recognized, and a new interface screen is created and then navigated to on the phone.
Is this right?
If I got the gist of that correct, why is the deal with the "R" class?
Why is it called to recognize the ID of the button?
I thought the super class (in this project) was the SudokuActivity class.

I want to take an integer and get its ordinal, i.e.:

    1 -&gt; &quot;First&quot;
    2 -&gt; &quot;Second&quot;
    3 -&gt; &quot;Third&quot;
    ...

Is there a way in Java to convert an integer to its ordinal name?

Trying to use the following code:

	List&lt;Integer&gt; list = new List&lt;Integer&gt;();

I get the following error message: 

&gt; `java.util.List` is abstract; cannot be instantiated

What does this mean and why can&#39;t I initialize a `List` the same way I would an `ArrayList`?

&quot;Instantiating&quot; a List in Java?

I found this older discussion: https://stackoverflow.com/questions/1452450/does-anyone-use-the-swingx-extensions-to-swing, but I am wondering the current status of SwingLabs, SwingX. A bunch of the download addresses etc are all broken, for example:

https://swingx.dev.java.net the first link on http://swinglabs.org/projects.jsp

https://swingx.dev.java.net/files/documents/2981/153005/swingx-1.6.2-bundle.zip the latest stable download

etc...

Is it simply a matter of substituting a new domain, or has Oracle gutted these activities?


What is the status of SwingLabs (SwingX) post acquisition

I can find in the [Maven docs](http://maven.apache.org/plugins/maven-surefire-plugin/examples/single-test.html) where it shows how to run:

 1. A single test
 2. All tests in a single test class
 3. All tests in classes matching a particular pattern

But how to run all the tests in a package? Is this possible?

I would prefer solutions that don&#39;t require modifying the `pom.xml` or code.

How to run all tests in a particular package with Maven?

I am attempting to do the equivalent of  

    if ( object1.class == object2.class )
    {
        //do something
    }  

which of course doesn&#39;t work, what method am I overlooking?


Determine if two Java objects are of the same class

I really like the new PopupMenu we got in 3.0, but I just can&#39;t display any icons next to the menu items in it. I&#39;m inflating the menu from the .xml below:

&lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot;?&gt;
&lt;menu xmlns:android=&quot;http://schemas.android.com/apk/res/android&quot;&gt;

	&lt;item android:id=&quot;@+id/menu_delete_product&quot;
		android:icon=&quot;@drawable/sym_action_add&quot;
		android:title=&quot;delete&quot;
		android:showAsAction=&quot;ifRoom|withText&quot; /&gt;
		
	&lt;item android:id=&quot;@+id/menu_modify_product&quot;
		android:icon=&quot;@drawable/sym_action_add&quot;
		android:title=&quot;modify&quot;
		android:showAsAction=&quot;ifRoom|withText&quot; /&gt;
	
	&lt;item android:id=&quot;@+id/menu_product_details&quot;
		android:icon=&quot;@drawable/sym_action_add&quot;
		android:title=&quot;details&quot;
		android:showAsAction=&quot;ifRoom|withText&quot; /&gt;
		
&lt;/menu&gt;

With this code:

    image.setOnClickListener(new View.OnClickListener() {
    	@Override
    	public void onClick(View v) {
    		PopupMenu pop = new PopupMenu(getActivity(), v);
    		pop.getMenuInflater().inflate(R.menu.shelves_details_menu, pop.getMenu());
    		pop.show();
   		}
    });

I can&#39;t get the icons to show up, am I missing something?

Is it possible to display icons in a PopupMenu?

i use the ViewPager for switching views with left/right swipe.

The ViewPager needs an Adapter, so I&#39;ve built this one:


    public class ListViewPagerAdapter extends PagerAdapter {

	protected static final String TAG = &quot;ListViewPagerAdapter&quot;;
	protected static final int NUM_VIEWS = 3;
	
	protected final Activity mActivity;
	
	public ListViewPagerAdapter(Activity activity) {
		mActivity = activity;
	}
	
	@Override
	public int getCount() {
		return NUM_VIEWS;
	}

	@Override
	public void startUpdate(View container) {}

	@Override
	public Object instantiateItem(View container, int position) {
		// ViewPager
		ViewPager viewPager = (ViewPager) container;
		
		// Wird verwendet, um die Views aufzurufen
		LayoutInflater layoutInflater = mActivity.getLayoutInflater();
		
		// Standardm&#228;&#223;ig ist news eingeblendet
		View view = layoutInflater.inflate(R.layout.news_fragment, null);
		// Falls sich die Position ver&#228;ndert, so ver&#228;ndert sich auch die View
		if (position == 0) {
			view = layoutInflater.inflate(R.layout.favorite_fragment, null);
		} else if (position == 2) {
			view = layoutInflater.inflate(R.layout.videos_fragment, null);
		}
		
		// View einblenden
		viewPager.addView(view, 0);
		
		return view;
	}

	@Override
	public void destroyItem(View container, int position, Object object) {
		// ViewPager
		ViewPager viewPager = (ViewPager) container;
		// View
		View view = (View) object;
		
		// View l&#246;schen
		viewPager.removeView(view);
	}

	@Override
	public void finishUpdate(View container) {}

	@Override
	public boolean isViewFromObject(View view, Object object) {
		View _view = (View) object;
		return view == _view;
	}

	@Override
	public Parcelable saveState() {
		return null;
	}

	@Override
	public void restoreState(Parcelable state, ClassLoader loader) {}
     }

Now, i want to get the current focused view by the viewpager.
I tried getChildAt(x), but it does not work.

Are there some example, or do you have any idea how to get the current view?

Thanks


Get focused View from ViewPager

&gt; **Possible Duplicate:**  
&gt; [Android Activity Life Cycle - difference between onPause() and OnStop()](https://stackoverflow.com/questions/8515936/android-activity-life-cycle-difference-between-onpause-and-onstop)  

&lt;!-- End of automatically inserted text --&gt;

I was wondering - **what is the difference between `onCreate()` and `onStart()` methods?**

I think that `onStart()` is a redundant method. `onCreate()` will ALWAYS be called (At least in my last two projects).

Can any one explain the difference?

Difference between onCreate() and onStart()?

My application installs other applications, and it needs to keep track of what applications it has installed. Of course, this could be achieved by simply keeping a list of installed applications. But this should not be necessary! It should be the responsibility of the PackageManager to maintain the installedBy(a, b) relationship. In fact, according to the API it is:

public abstract String &lt;b&gt;getInstallerPackageName&lt;/b&gt;(String packageName) - 
&lt;i&gt;Retrieve the package name of the application that installed a package. This identifies which market the package came from.&lt;/i&gt;

&lt;h2&gt;The current approach&lt;/h2&gt;
&lt;b&gt;Install APK using Intent&lt;/b&gt;

    Intent intent = new Intent(Intent.ACTION_VIEW);
    intent.setDataAndType(apkUri, &quot;application/vnd.android.package-archive&quot;);
    startActivity(intent);

&lt;b&gt;Uninstall APK using Intent:&lt;/b&gt;

    Intent intent = new Intent(Intent.ACTION_DELETE, Uri.fromParts(&quot;package&quot;,
    getPackageManager().getPackageArchiveInfo(apkUri.getPath(), 0).packageName,null));
    startActivity(intent);

This is obviously not the way e.g. Android Market installs / uninstalls packages. They use a richer version of the PackageManager. This can bee seen by downloading the Android source code from the Android Git repository. Below are the two hidden methods that corresponds to the Intent approach. Unfortunately they are not available to external developers. But perhaps they will be in the future?

&lt;h2&gt;The better approach&lt;/h2&gt;

&lt;b&gt;Installing APK using the PackageManager&lt;/b&gt;

    /**
     * @hide
     * 
     * Install a package. Since this may take a little while, the result will
     * be posted back to the given observer.  An installation will fail if the calling context
     * lacks the {@link android.Manifest.permission#INSTALL_PACKAGES} permission, if the
     * package named in the package file&#39;s manifest is already installed, or if there&#39;s no space
     * available on the device.
     *
     * @param packageURI The location of the package file to install.  This can be a &#39;file:&#39; or a
     * &#39;content:&#39; URI.
     * @param observer An observer callback to get notified when the package installation is
     * complete. {@link IPackageInstallObserver#packageInstalled(String, int)} will be
     * called when that happens.  observer may be null to indicate that no callback is desired.
     * @param flags - possible values: {@link #INSTALL_FORWARD_LOCK},
     * {@link #INSTALL_REPLACE_EXISTING}, {@link #INSTALL_ALLOW_TEST}.
     * @param installerPackageName Optional package name of the application that is performing the
     * installation. This identifies which market the package came from.
     */
    public abstract void installPackage(
            Uri packageURI, IPackageInstallObserver observer, int flags,
            String installerPackageName);

&lt;b&gt;Uninstalling APK using the PackageManager&lt;/b&gt;

    /**
     * Attempts to delete a package.  Since this may take a little while, the result will
     * be posted back to the given observer.  A deletion will fail if the calling context
     * lacks the {@link android.Manifest.permission#DELETE_PACKAGES} permission, if the
     * named package cannot be found, or if the named package is a &quot;system package&quot;.
     * (TODO: include pointer to documentation on &quot;system packages&quot;)
     *
     * @param packageName The name of the package to delete
     * @param observer An observer callback to get notified when the package deletion is
     * complete. {@link android.content.pm.IPackageDeleteObserver#packageDeleted(boolean)} will be
     * called when that happens.  observer may be null to indicate that no callback is desired.
     * @param flags - possible values: {@link #DONT_DELETE_DATA}
     *
     * @hide
     */
    public abstract void deletePackage(
            String packageName, IPackageDeleteObserver observer, int flags);


&lt;h2&gt;Differences&lt;/h2&gt;
* When using intents the local package manager is not made aware of which application the installation originated from. Specifically, getInstallerPackageName(...) returns null.
 
* The hidden method installPackage(...) takes the installer package name as a parameter, and is most likely capable of setting this value.

&lt;h2&gt;Question&lt;/h2&gt;
&lt;b&gt;Is it possible to specify package installer name using intents?&lt;/b&gt; 
&lt;i&gt;(Maybe the name of the installer package can be added as an extra to the installation intent?)&lt;/i&gt; 


&lt;i&gt;Tip: If you want to download the Android source code you can follow the steps described here: &lt;a href=&quot;http://source.android.com/source/downloading.html&quot;).&gt;Downloading the Source Tree&lt;/a&gt;. To extract the *.java files and put them in folders according to the package hierarchy you can check out this neat script: &lt;a href=&quot;http://blog.michael-forster.de/2008/12/view-android-source-code-in-eclipse.html&quot;&gt;View Android Source Code in Eclipse&lt;/a&gt;.&lt;/i&gt;

install / uninstall APKs programmatically (PackageManager vs Intents)

I need to develop an app that has the share function. I have to share on Facebook, twitter, email and maybe other services. 

How can I do this? There a library on the net? For the iOS development there were ShareKit, but for Android?

Thanks :)

Content Type	Original Author	Original Content on Stackoverflow
Question	Skizz	View Question on Stackoverflow
Solution 1 - Java	omermuhammed	View Answer on Stackoverflow
Solution 2 - Java	xandy	View Answer on Stackoverflow
Solution 3 - Java	Alex Gitelman	View Answer on Stackoverflow

Understand the R class in Android

Java Problem Overview

Java Solutions

Solution 1 - Java

Solution 2 - Java

Solution 3 - Java

Why can a string be assigned to a char* pointer, but not to a char[] array?

JPA @OneToOne with Shared ID -- Can I do this Better?

Attributions