First retrieve the field property of the class, then you can retrieve the value. If you know the type you can use one of the get methods with null (for static fields only, in fact with a static field the argument passed to the get method is ignored entirely). Otherwise you can use getType and write an appropriate switch as below:

    Field f = R.class.getField(&quot;_1st&quot;);
    Class&lt;?&gt; t = f.getType();
    if(t == int.class){
        System.out.println(f.getInt(null));
    }else if(t == double.class){
        System.out.println(f.getDouble(null));
    }...

     R.class.getField(&quot;_1st&quot;).get(null);

Exception handling is left as an exercise for the reader.

Basically you get the field like any other via reflection, but when you call the get method you pass in a null since there is no instance to act on.

This works for all static fields, regardless of their being final. If the field is not public, you need to call `setAccessible(true)` on it first, and of course the SecurityManager has to allow all of this.

I was following the same route (looking through the generated R class) and then I had this awful feeling it was probably a function in the Resources class. I was right. 

Found this:
[Resources::getIdentifier][1]


  [1]: http://developer.android.com/reference/android/content/res/Resources.html#getIdentifier%28java.lang.String,%20java.lang.String,%20java.lang.String%29 

Thought it might save people some time. Although they say its discouraged in the docs, which is not too surprising. 

I&#39;m looking for a database to pair with a node.js app. I&#39;m assuming a json/nosql db would be preferable to a relational DB [I can do without any json/sql impedance mismatch]. I&#39;m considering:

- couchdb
- mongodb
- redis

Anyone have any views / war stories re compatiability/deployability of the above with node.js? Any clear favorites?


node.js database

I have two Activities A and B. I want to have the shrink Animation when 
Activity A calls B and maximize animation when Activity B calls A. I don&#39;t need the animation xml files for this.

When we call another Activity in Android it gives its default animation and then it calls shrink animation. 

What I want is that the default animation should not occur and the animation that I want should occur.

Can we actually give the animation when calling another Activity?



How to provide animation when calling another activity in Android?

Say I have a class:

    public class R {
        public static final int _1st = 0x334455;
    }

How can I get the value of the **&quot;_1st&quot;** via reflection?

Getting value of public static final field/property of a class in Java via reflection

Say I have a class:
<pre><code class="hljs language-arduino">public class R {
 public static final int _1st = 0x334455;
}
</code></pre>
How can I get the value of the "_1st" via reflection?

If I have two multiple threads accessing a HashMap, but guarantee that they&#39;ll never be accessing the same key at the same time, could that still lead to a race condition?

Is a HashMap thread-safe for different keys?

I want a list of dates between start date and end date.  

The result should be a list of all dates including the start and end date.  

how to get a list of dates between two dates in java

In C# we have `Type.FullName` and `Type.Name` for getting the name of a type (class in this case) with or without the namespace (package in java-world).

What is the java equivalent to `Type.Name`?

Clearly there must be a better way than using `Class.getName()` and strip it of the package name manually. 

How to get the name of a class without the package?

I&#39;m using `LinkedBlockingQueue` between two different threads. One thread adds data via `add`, while the other thread receives data via `take`.

My question is, do I need to synchronize access to `add` and `take`. Is `LinkedBlockingQueue`&#39;s insert and remove methods thread safe?

Are LinkedBlockingQueue&#39;s insert and remove methods thread safe?

How do I bypass invalid SSL certificate errors with Apache [HttpClient][1] 4.0?

  [1]: http://hc.apache.org/httpclient-3.x/


How to ignore SSL certificate errors in Apache HttpClient 4.0

I&#39;m playing around with the C# reflection API. I can easily load `Type` information of classes, methods etc. in an assembly, however, now I wonder how can I load and read the code inside a method?

Can I use reflection to inspect the code in a method?

To check if a type is a subclass of another type in C#, it&#39;s easy:

    typeof (SubClass).IsSubclassOf(typeof (BaseClass)); // returns true

However, this will fail:

    typeof (BaseClass).IsSubclassOf(typeof (BaseClass)); // returns false

Is there any way to check whether a type is either a subclass OR of the base class itself, without using an `OR` operator or using an extension method?

How do I check if a type is a subtype OR the type of an object?

Having a chain of &quot;instanceof&quot; operations is considered a &quot;code smell&quot;.  The standard answer is &quot;use polymorphism&quot;.  How would I do it in this case?

There are a number of subclasses of a base class; none of them are under my control.  An analogous situation would be with the Java classes Integer, Double, BigDecimal etc.

    if (obj instanceof Integer) {NumberStuff.handle((Integer)obj);}
    else if (obj instanceof BigDecimal) {BigDecimalStuff.handle((BigDecimal)obj);}
    else if (obj instanceof Double) {DoubleStuff.handle((Double)obj);}

I do have control over NumberStuff and so on.

I don&#39;t want to use many lines of code where a few lines would do.  (Sometimes I make a HashMap mapping Integer.class to an instance of IntegerStuff, BigDecimal.class to an instance of BigDecimalStuff etc.  But today I want something simpler.)

I&#39;d like something as simple as this:

    public static handle(Integer num) { ... }
    public static handle(BigDecimal num) { ... }

But Java just doesn&#39;t work that way.

I&#39;d like to use static methods when formatting.  The things I&#39;m formatting are composite, where a Thing1 can contain an array Thing2s and a Thing2 can contain an array of Thing1s.  I had a problem when I implemented my formatters like this:

    class Thing1Formatter {
      private static Thing2Formatter thing2Formatter = new Thing2Formatter();
      public format(Thing thing) {
          thing2Formatter.format(thing.innerThing2);
      }
    }
    class Thing2Formatter {
      private static Thing1Formatter thing1Formatter = new Thing1Formatter();
      public format(Thing2 thing) {
          thing1Formatter.format(thing.innerThing1);
      }
    }

Yes, I know the HashMap and a bit more code can fix that too.  But the &quot;instanceof&quot; seems so readable and maintainable by comparison.  Is there anything simple but not smelly?

Note added 5/10/2010:

It turns out that new subclasses will probably be added in the future, and my existing code will have to handle them gracefully.  The HashMap on Class won&#39;t work in that case because the Class won&#39;t be found.  A chain of if statements, starting with the most specific and ending with the most general, is probably the best after all:

    if (obj instanceof SubClass1) {
        // Handle all the methods and properties of SubClass1
    } else if (obj instanceof SubClass2) {
        // Handle all the methods and properties of SubClass2
    } else if (obj instanceof Interface3) {
        // Unknown class but it implements Interface3
        // so handle those methods and properties
    } else if (obj instanceof Interface4) {
        // likewise.  May want to also handle case of
        // object that implements both interfaces.
    } else {
        // New (unknown) subclass; do what I can with the base class
    }


Avoiding instanceof in Java

During the last years I always thought that in Java, Reflection is widely used during Unit testing. Since some of the variables/methods which have to be checked are private, it is somehow necessary to read the values of them. I always thought that the Reflection API is also used for this purpose.

Last week i had to test some packages and therefore write some JUnit tests. As always i used Reflection to access private fields and methods. But my supervisor who checked the code wasn&#39;t really happy with that and told me that the Reflection API wasn&#39;t meant to use for such &quot;hacking&quot;. Instead he suggested to modifiy the visibility in the production code.

Is it really bad practice to use Reflection? I can&#39;t really believe that-

Edit: I should have mentioned that i was required that all tests are in a separate package called test (so using protected visibilty e.g. wasn&#39;t a possible solution too)

Is it bad practice to use Reflection in Unit testing?

(See below solution I created using the answer I accepted)

I&#39;m trying to improve the maintainability of some code involving reflection. The app has a .NET Remoting interface exposing (among other things) a method called `Execute` for accessing parts of the app not included in its published remote interface. 

Here is how the app designates properties (a static one in this example) which are meant to be accessible via Execute:

    RemoteMgr.ExposeProperty(&quot;SomeSecret&quot;, typeof(SomeClass), &quot;SomeProperty&quot;);

So a remote user could call: 

    string response = remoteObject.Execute(&quot;SomeSecret&quot;);

and the app would use reflection to find SomeClass.SomeProperty and return its value as a string.

Unfortunately, if someone renames SomeProperty and forgets to change the 3rd parm of ExposeProperty(), it breaks this mechanism.

I need to the equivalent of: 

    SomeClass.SomeProperty.GetTheNameOfThisPropertyAsAString()

to use as the 3rd parm in `ExposeProperty` so refactoring tools would take care of renames.

Is there a way to do this?

Okay, here&#39;s what I ended up creating (based upon the answer I selected and the question he referenced):

    // &lt;summary&gt;
    // Get the name of a static or instance property from a property access lambda.
    // &lt;/summary&gt;
    // &lt;typeparam name=&quot;T&quot;&gt;Type of the property&lt;/typeparam&gt;
    // &lt;param name=&quot;propertyLambda&quot;&gt;lambda expression of the form: &#39;() =&gt; Class.Property&#39; or &#39;() =&gt; object.Property&#39;&lt;/param&gt;
    // &lt;returns&gt;The name of the property&lt;/returns&gt;
    public string GetPropertyName&lt;T&gt;(Expression&lt;Func&lt;T&gt;&gt; propertyLambda)
    {
        var me = propertyLambda.Body as MemberExpression;
    
        if (me == null)
        {
            throw new ArgumentException(&quot;You must pass a lambda of the form: &#39;() =&gt; Class.Property&#39; or &#39;() =&gt; object.Property&#39;&quot;);
        }
    
        return me.Member.Name;
     }

Usage:

    // Static Property
    string name = GetPropertyName(() =&gt; SomeClass.SomeProperty);
    
    // Instance Property
    string name = GetPropertyName(() =&gt; someObject.SomeProperty);

Now with this cool capability, it&#39;s time to simplify the ExposeProperty method. Polishing doorknobs is dangerous work...


Get name of property as a string

I have Python classes, of which I need only one instance at runtime, so it would be sufficient to have the attributes only once per class and not per instance. If there would be more than one instance (which won&#39;t happen), all instance should have the same configuration. I wonder which of the following options would be better or more &quot;idiomatic&quot; Python.

Class variables:

    class MyController(Controller):

      path = &quot;something/&quot;
      children = [AController, BController]
      
      def action(self, request):
        pass

Instance variables:

    class MyController(Controller):

      def __init__(self):
        self.path = &quot;something/&quot;
        self.children = [AController, BController]
      
      def action(self, request):
        pass



Instance variables vs. class variables in Python

Why does `extern int n` not compile when n is declared (in a different file) `static int n`, but works when declared `int n`?  (Both of these declarations were at file scope.)  

Basically, why is `int n` in file scope not the same as `static int n` in the same scope?  Is it only in relation to extern?  If so, what about extern am I missing?

Why can&#39;t you call abstract functions from abstract classes in PHP?

I was looking over some code the other day and I came across:

    static {
        ...
    }
Coming from C++, I had no idea why that was there. Its not an error because the code compiled fine. What is this &quot;static&quot; block of code?

Static Block in Java

I have a C project that produces ten executables, all of which I would like to be linked in statically. The problem I am facing is that one of these executables uses a 3rd-party library of which only the shared-object version is available.

  If I pass the `-static` flag to gcc, ld will error saying it can&#39;t find the library in question (I presume it&#39;s looking for the .a version) and the executable will not be built.  Ideally, I would like to be able to tell &#39;ld&#39; to statically link as much as it can and fail over to the shared object library if a static library cannot be found.

In the interium I tried something like `gcc -static -lib1 -lib2 -shared -lib3rdparty foo.c -o foo.exe` in hopes that &#39;ld&#39; would statically link in lib1 and lib2 but only have a run-time dependence on lib3rdparty. Unfortunatly, this did not work as I intended; instead the `-shared` flag overwrote the `-static` flag and everything was compiled as shared-objects.

Is statically linking an all-or-nothing deal, or is there some way I can mix and match?

Can I mix static and shared-object libraries when linking?

I was trying to identify the reason behind constants in Java
I have learned that Java allows us to declare constants by using `final` keyword.

My question is why didn&#39;t Java introduce a Constant (`const`) feature. Since many people say it has come from C++, in C++ we have `const` keyword.

Please share your thoughts.


Why is there no Constant feature in Java?

In `ArrayBlockingQueue`, all the methods that require the lock copy it to a local `final` variable before calling `lock()`.

    public boolean offer(E e) {
        if (e == null) throw new NullPointerException();
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            if (count == items.length)
                return false;
            else {
                insert(e);
                return true;
            }
        } finally {
            lock.unlock();
        }
    }

Is there any reason to copy `this.lock` to a local variable `lock` when the field `this.lock` is `final`?

Additionally, it also uses a local copy of `E[]` before acting on it:

    private E extract() {
        final E[] items = this.items;
        E x = items[takeIndex];
        items[takeIndex] = null;
        takeIndex = inc(takeIndex);
        --count;
        notFull.signal();
        return x;
    }

Is there any reason for copying a final field to a local final variable?

In ArrayBlockingQueue, why copy final member field into local final variable?

I have an class defining an immutable value type that I now need to serialize. The immutability comes from the final fields which are set in the constructor. I&#39;ve tried serializing, and it works (surprisingly?) - but I&#39;ve no idea how.

Here&#39;s an example of the class

    public class MyValueType implements Serializable
    {
        private final int value;
    
        private transient int derivedValue;
    
        public MyValueType(int value)
        {
            this.value = value;
            this.derivedValue = derivedValue(value);
        }
    
        // getters etc...
    }

Given that the class doesn&#39;t have a no arg constructor, how can it be instantiated and the final field set? 

(An aside - I noticed this class particularly because IDEA wasn&#39;t generating a &quot;no serialVersionUID&quot; inspection warning for this class, yet successfully generated warnings for other classes that I&#39;ve just made serializable.)




How does java serialization deserialize final fields when no default constructor specified?

Is it possible to have `final transient` fields that are set to any non-default value after serialization in Java?  My usecase is a cache variable — that&#39;s why it is `transient`.  I also have a habit of making `Map` fields that won&#39;t be changed (i.e. contents of the map is changed, but object itself remains the same) `final`.  However, these attributes seem to be contradictory — while compiler allows such a combination, I cannot have the field set to anything but `null` after unserialization.

I tried the following, without success:

* simple field initialization (shown in the example): this is what I normally do, but the initialization doesn&#39;t seem to happen after unserialization;
* initialization in constructor (I believe this is semantically the same as above though);
* assigning the field in `readObject()` — cannot be done since the field is `final`.

In the example `cache` is `public` only for testing.

    import java.io.*;
    import java.util.*;

    public class test
    {
        public static void main (String[] args) throws Exception
        {
            X  x = new X ();
            System.out.println (x + &quot; &quot; + x.cache);

            ByteArrayOutputStream  buffer = new ByteArrayOutputStream ();
            new ObjectOutputStream (buffer).writeObject (x);
            x = (X) new ObjectInputStream (new ByteArrayInputStream (buffer.toByteArray ())).readObject ();
            System.out.println (x + &quot; &quot; + x.cache);
        }

        public static class X implements Serializable
        {
            public final transient Map &lt;Object, Object&gt;  cache = new HashMap &lt;Object, Object&gt; ();
        }
    }

Output:

    test$X@1a46e30 {}
    test$X@190d11 null



final transient fields and serialization

I have a class with a `private static final` field that, unfortunately, I need to change it at run-time.

Using reflection I get this error: `java.lang.IllegalAccessException: Can not set static final boolean field`

Is there any way to change the value?

    Field hack = WarpTransform2D.class.getDeclaredField(&quot;USE_HACK&quot;);
    hack.setAccessible(true);
    hack.set(null, true);

Content Type	Original Author	Original Content on Stackoverflow
Question	Viet	View Question on Stackoverflow
Solution 1 - Java	M. Jessup	View Answer on Stackoverflow
Solution 2 - Java	Yishai	View Answer on Stackoverflow
Solution 3 - Java	Brian	View Answer on Stackoverflow

Getting value of public static final field/property of a class in Java via reflection

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How to provide animation when calling another activity in Android?

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