Here&#39;s a a couple of useful link that I found when I started with JNI

http://en.wikipedia.org/wiki/Java_Native_Interface  
http://download.oracle.com/javase/1.5.0/docs/guide/jni/spec/functions.html

concerning your problem you can use this 

    JNIEXPORT void JNICALL Java_ClassName_MethodName(JNIEnv *env, jobject obj, jstring javaString)   
    {
       const char *nativeString = env-&gt;GetStringUTFChars(javaString, 0);
        
       // use your string
        
       env-&gt;ReleaseStringUTFChars(javaString, nativeString);
    }



Thanks Jason Rogers&#39;s answer first.

In **Android** &amp;&amp; **cpp** should be this:

	const char *nativeString = env-&gt;GetStringUTFChars(javaString, nullptr);

	// use your string

	env-&gt;ReleaseStringUTFChars(javaString, nativeString);
Can fix this errors:

1.error: base operand of &#39;-&gt;&#39; has non-pointer type &#39;JNIEnv {aka _JNIEnv}&#39;

2.error: no matching function for call to &#39;_JNIEnv::GetStringUTFChars(JNIEnv*&amp;, _jstring*&amp;, bool)&#39;


3.error: no matching function for call to &#39;_JNIEnv::ReleaseStringUTFChars(JNIEnv*&amp;, _jstring*&amp;, char const*&amp;)&#39;

4.add &quot;env-&gt;DeleteLocalRef(nativeString);&quot; at end.

When should a View actually be used over an actual Table? What gains should I expect this to produce?

Overall, what are the advantages of using a view over a table? Shouldn&#39;t I design the table in the way the view should look like in the first place?

When to use a View instead of a Table?

I have a throbber that is to appear when a user clicks a link.

The problem is is that that same link can be clicked and dragged to be rearranged. In this case, I wouldn&#39;t need the throbber to appear. It only needs to appear if its actually waiting to go somewhere.

How can I, with jQuery, create an event listener that would only **allow a throbber to appear if its a click through to a link**, and not a click and drag?

Can you detect &quot;dragging&quot; in jQuery?

I have passed a URL string from Java to C code as `jstring` data type through the use of JNI. And my library method needs a `char *` as url.

 How can I convert `jstring` in `char *` ?


 P.S.: Is there any advantage of using jcharArray in C? (i.e. Passing `char []` instead of string in native method)

JNI converting jstring to char *

I have passed a URL string from Java to C code as <code>jstring</code> data type through the use of JNI. And my library method needs a <code>char *</code> as url.
How can I convert <code>jstring</code> in <code>char *</code> ?
P.S.: Is there any advantage of using jcharArray in C? (i.e. Passing <code>char []</code> instead of string in native method)

[Apache Commons IO][1] has a nice convenience method [IOUtils.toString()][2] to read an `InputStream` to a String.

Since I am trying to move away from Apache Commons and to [Guava][3]: is there an equivalent in Guava? I looked at all classes in the `com.google.common.io` package and I couldn&#39;t find anything nearly as simple.

**Edit:** I understand and appreciate the issues with charsets. It just so happens that I know that all my sources are in ASCII (yes, ASCII, not ANSI etc.), so in this case, encoding is not an issue for me.


  [1]: http://commons.apache.org/io
  [2]: http://commons.apache.org/io/api-release/org/apache/commons/io/IOUtils.html#toString%28java.io.InputStream%29
  [3]: http://code.google.com/p/guava-libraries/

Guava equivalent for IOUtils.toString(InputStream)

From Eclipse, I found **I can easily export an Ant build file for my project**. It provides references to 3rd party libraries and some base targets. I&#39;m using it from my global build file. The only thing that bothers me about this, is that if something is modified in the project structure (like adding a new 3rd party library), we have to think (yes that can be hard sometimes!) about regenerating that build.xml file. **I&#39;m wondering if anyone here knows a way to have it updated automatically.** By &quot;automatically&quot; I mean that it would not be necessary to explicitly ask Eclipse to regenerate it every time it&#39;s needed. I don&#39;t know what could be the trigger though...

Any thoughts or knowledge on this?

Thanks!

MJ

Any way to generate ant build.xml file automatically from Eclipse?

Are there any functions (as part of a math library) which will calculate [mean][1], median, mode and range from a set of numbers. 


  [1]: http://www.cimt.plymouth.ac.uk/projects/mepres/book8/bk8i5/bk8_5i2.htm

How to calculate mean, median, mode and range from a set of numbers

I have a ListActivity with my customized adapter and inside each of the view, it may have some buttons, in which I need to implement `OnClickListener`. I need to implement the `OnClickListener` in the adapter. However, I don&#39;t know how to call the function like `startActivity()` or `setResult()`. Since the adapter doesn&#39;t extend to Activity. 

So what is the best way to solve this problem? 

Thanks.




How to start Activity in adapter?

At work it seems like no week ever passes without some encoding-related conniption, calamity, or catastrophe.  The problem usually derives from programmers who think they can reliably process a “text” file without specifying the encoding.  But you can&#39;t.

So it&#39;s been decided to henceforth forbid files from ever having names that end in `*.txt` or `*.text`.  The thinking is that those extensions mislead the casual programmer into a dull complacency regarding encodings, and this leads to improper handling.  It would almost be better to have no
extension at all, because at least then you *know* that you don’t know what you’ve got.

However, we aren’t goint to go that far.  Instead you will be expected to use a filename that ends in the encoding.  So for text files, for example, these would be something like `README.ascii`, `README.latin1`, `README.utf8`, etc.

For files that demand a particular extension, if one can specify the encoding inside the file itself, such as in Perl or Python, then you shall do that.  For files like Java source where no such facility exists internal to the file, you will put the encoding before the extension, such as `SomeClass-utf8.java`.

For output, UTF-8 is to be **strongly** preferred.

But for input, we need to figure out how to deal with the thousands of files in our codebase named `*.txt`.  We want to rename all of them to fit into our new standard.  But we can’t possibly eyeball them all.  So we need a library or program that actually works.

These are variously in ASCII, ISO-8859-1, UTF-8, Microsoft CP1252, or Apple MacRoman.  Although we&#39;re know we can tell if something is ASCII, and we stand a good change of knowing if something is probably UTF-8, we’re stumped about the 8-bit encodings.  Because we’re running in a mixed Unix environment (Solaris, Linux, Darwin) with most desktops being Macs, we have quite a few annoying MacRoman files.  And these especially are a problem.

For some time now I’ve been looking for a way to programmatically determine which of

1. ASCII
2. ISO-8859-1
3. CP1252
4. MacRoman
5. UTF-8

a file is in, and I haven’t found a program or library that can reliably distinguish between those the three different 8-bit encodings.  We probably have over a thousand MacRoman files alone, so whatever charset detector we use has to be able to sniff those out.  Nothing I’ve looked at can manage the trick.  I had big hopes for the [ICU charset detector library](http://userguide.icu-project.org/conversion/detection#TOC-CharsetDetector), but it cannot handle MacRoman.  I’ve also looked at modules to do the same sort of thing in both Perl and Python, but again and again it’s always the same story: no support for detecting MacRoman.

What I am therefore looking for is an existing library or program that reliably determines which of those five encodings a file is in—and preferably more than that.  In particular it has to distinguish between the three 3-bit encoding I’ve cited, **especially MacRoman**.  The files are more than 99% English language text; there are a few in other languages, but not many.

If it’s library code, our language preference is for it to be in Perl, C, Java, or Python, and in that order.  If it’s just a program, then we don’t really care what language it’s in so long as it comes in full source, runs on Unix, and is fully unencumbered.

Has anyone else had this problem of a zillion legacy text files randomly encoded?  If so, how did you attempt to solve it, and how successful were you?  This is the most important aspect of my question, but I’m also interested in whether you think encouraging programmers to name (or rename) their files with the actual encoding those files are in will help us avoid the problem in the future.   Has anyone ever tried to enforce this on an institutional basis, and if so, was *that* successful or not, and why?

And yes, I fully understand why one cannot guarantee a definite answer given the nature of the problem.   This is especially the case with small files, where you don’t have enough data to go on. Fortunately, our files are seldom small. Apart from the random `README` file, most are in the size range of 50k to 250k, and many are larger.  Anything more than a few K in size is guaranteed to be in English.

 The problem domain is biomedical text mining, so we sometimes deal with extensive and extremely large corpora, like all of PubMedCentral’s Open Access respository.   A rather huge file is the BioThesaurus 6.0, at 5.7 gigabytes. This file is especially annoying because it is *almost* all UTF-8.  However, some numbskull went and stuck a few lines in it that are in some 8-bit encoding—Microsoft CP1252, I believe.  It takes quite a while before you trip on that one. :(

How to reliably guess the encoding between MacRoman, CP1252, Latin1, UTF-8, and ASCII

What is wrong with my make file?

Android.mk

    LOCAL_PATH := $(call my-dir)
     
    include $(CLEAR_VARS)
    LOCAL_MODULE    := foo
    LOCAL_SRC_FILES := foo.c
    LOCAL_EXPORT_LDLIBS := -llog
    include $(BUILD_SHARED_LIBRARY)

foo.c

    #include &lt;string.h&gt;
    #include &lt;jni.h&gt;
    #include &lt;android/log.h&gt;
    
    #define  LOG_TAG    &quot;foo&quot;
    #define  LOGI(...)  __android_log_print(ANDROID_LOG_INFO, LOG_TAG, __VA_ARGS__)
     
    void test() {
        LOGI(&quot;test&quot;);
    }

ndk-build

    foo.c:9: undefined reference to `__android_log_print&#39;

undefined reference to `__android_log_print&#39;

I&#39;m looking for a way to easily debug C code in an Android NDK application using Eclipse.  I&#39;ve read ways to debug the app using gdb or something similar but what I want is a way to push messages to Eclipse somehow.

I&#39;m looking for a solution that&#39;s as simple as using a print function in C and seeing it in the DDMS Log or anything similar.  Does anyone have any experience doing this?

Any simple way to log in Android NDK code?

I&#39;m working with JNI and have an array of type jbyte, where jbyte is represented as an signed char i.e. ranging from -128 to 127. The jbytes represent image pixels. For image processing, we usually want pixel components to range from 0 to 255. I therefore want to convert the jbyte value to the range 0 to 255 (i.e. the same range as unsigned char), do some calculations on the value and then store the result as a jbyte again.

How can I do these conversion safely? 

I managed to get this code to work, where a pixel value is incremented by 30 but clamped to the value 255, but I don&#39;t understand if it&#39;s safe or portable:

     #define CLAMP255(v) (v &gt; 255 ? 255 : (v &lt; 0 ? 0 : v))

     jbyte pixel = ...
     pixel = CLAMP_255((unsigned char)pixel + 30);

I&#39;m interested to know how to do this in both C and C++.

Converting from signed char to unsigned char and back again?

I have some C code for Android that does lots of low-level number crunching. I&#39;d like to know what settings I should use (e.g. for my Android.mk and Application.mk) files so that the code produced will run on all current Android devices but also takes advantage of optimisations for specific chipsets. I&#39;m looking for good default Android.mk and Application.mk settings to use and I want to avoid having to litter my C code with #ifdef branches.

For example, I&#39;m aware that ARMv7 has floating point instructions and some ARMv7 chips support NEON instructions and that the default ARM supports neither of these. Is it possible to set flags so that I can build ARMv7 with NEON, ARMv7 without NEON and the default ARM build? I&#39;m know how to do the latter two but not all 3. I&#39;m cautious about what settings I use as I assume the current defaults are the safest settings and what risks other options have.

For GCC specific optimisation, I&#39;m using the following flags:

    LOCAL_CFLAGS=-ffast-math -O3 -funroll-loops

I&#39;ve checked all 3 of these speed up my code. Are there any other common ones I could add?

Another tip I have is to add &quot;LOCAL_ARM_MODE := arm&quot; to Android.mk to enable a speed up on newer arm chips (although I&#39;m confused at exactly what this does and what happens on older chips).


Producing optimised NDK code for multiple architectures?

I&#39;m trying to get a simple Java method call from C++ while Java calls native method. Here&#39;s the Java code:

    public class MainActivity extends Activity {
        private static String LIB_NAME = &quot;name&quot;;
    
        static {
            System.loadLibrary(LIB_NAME);
        }
    
        /** Called when the activity is first created. */
        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.main);
            TextView tv = (TextView) findViewById(R.id.textview);
            tv.setText(this.getJniString());
        }
    
        public void messageMe(String text) {
            System.out.println(text);
        }
    
        public native String getJniString();
    }

I&#39;m trying to call `messageMe` method from native code in the process of `getJniString*` method call from Java to native.

native.cpp:

    #include &lt;string.h&gt;
    #include &lt;stdio.h&gt;
    #include &lt;jni.h&gt;
    
    jstring Java_the_package_MainActivity_getJniString( JNIEnv* env, jobject obj, jint depth ){
    
    //    JavaVM *vm;
    //    JNIEnv *env;
    //    JavaVMInitArgs vm_args;
    //    vm_args.version = JNI_VERSION_1_2;
    //    vm_args.nOptions = 0;
    //    vm_args.ignoreUnrecognized = 1;
    //
    //    // Construct a VM
    //    jint res = JNI_CreateJavaVM(&amp;vm, (void **)&amp;env, &amp;vm_args);
    
        // Construct a String
        jstring jstr = env-&gt;NewStringUTF(&quot;This string comes from JNI&quot;);
        // First get the class that contains the method you need to call
        jclass clazz = env-&gt;FindClass(&quot;the/package/MainActivity&quot;);
        // Get the method that you want to call
        jmethodID messageMe = env-&gt;GetMethodID(clazz, &quot;messageMe&quot;, &quot;(Ljava/lang/String;)V&quot;);
        // Call the method on the object
        jobject result = env-&gt;CallObjectMethod(jstr, messageMe);
        // Get a C-style string
        const char* str = env-&gt;GetStringUTFChars((jstring) result, NULL);
        printf(&quot;%s\n&quot;, str);
            // Clean up
        env-&gt;ReleaseStringUTFChars(jstr, str);
    
    //    // Shutdown the VM.
    //    vm-&gt;DestroyJavaVM();
    
        return env-&gt;NewStringUTF(&quot;Hello from JNI!&quot;);
    }


After clean compilation app stops with next message:

    ERROR/AndroidRuntime(742): FATAL EXCEPTION: main
            java.lang.NoSuchMethodError: messageMe
            at *.android.t3d.MainActivity.getJniString(Native Method)
            at *.android.t3d.MainActivity.onCreate(MainActivity.java:22)

Apparently it means that method name is wrong, but it looks OK to me. 


Content Type	Original Author	Original Content on Stackoverflow
Question	Prasham	View Question on Stackoverflow
Solution 1 - Java	Jason Rogers	View Answer on Stackoverflow
Solution 2 - Java	kangear	View Answer on Stackoverflow

JNI converting jstring to char *

Java Problem Overview

Java Solutions

Solution 1 - Java

Solution 2 - Java

Can you detect "dragging" in jQuery?

When to use a View instead of a Table?

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