`Sampling` means taking lots of thread dumps and analyzing stack traces.
This is usually faster, does not require runtime changes in your bytecode (which may break it), but is also less accurate.

`Profiling` means [instrumenting][1] your classes and methods, so they &quot;report&quot; whenever they are run. This is more accurate, as it counts every invocation of instrumented method, not only those caught when the dump is done. However instrumentation means that the bytecode of your classes is changed, and this may break your program. Actually, for that reason, using profiling on large application servers (like JBoss, or WebLogic) often causes everything to die or hang.


[1]: https://docs.oracle.com/en/java/javase/16/docs/api/java.instrument/java/lang/instrument/Instrumentation.html

I don&#39;t need to terminate the thread correctly, or make it respond to a &quot;terminate&quot; command. I am interested in terminating the thread forcefully using pure C++11.

How do I terminate a thread in C++11?

I&#39;m developing an app on Heroku with a Postgresql backend. Periodically, I get this error message when trying to access the database, both from the CLI and from loading a page on the server:

    psql: FATAL: remaining connection slots are reserved for non-replication superuser connections

Anyone seen this before or please help point me in the right direction?

Heroku &quot;psql: FATAL: remaining connection slots are reserved for non-replication superuser connections&quot;

VisualVM has two separate tabs for sampling and profiling. What is the difference between sampling and profiling in VisualVM?

Difference between sampling and profiling in jVisualVM

<p>VisualVM has two separate tabs for sampling and profiling. What is the difference between sampling and profiling in VisualVM?</p>


When I rotate my screen, the WebView reloads the whole page. I can&#39;t have this since some of my content contains dynamic/random material. Currently when rotated the screen reloads the original URL from the loadUrl() method. 

Any idea what&#39;s wrong with my code? 

***MainActivity.java***


    package com.mark.myapp;
    
    import android.app.Activity;
    import android.os.Bundle;
    import android.util.Log;
    import android.view.KeyEvent;
    import android.view.Menu;
    import android.webkit.WebView;
    import android.webkit.WebViewClient;
    
    public class MainActivity extends Activity {
    
    	WebView web;
    	String webURL = &quot;http://www.google.co.uk/&quot;;
    	
        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            
            if (savedInstanceState != null)
                ((WebView)findViewById(R.id.web)).restoreState(savedInstanceState);
            
            web = (WebView) findViewById(R.id.web);
            web.getSettings().setJavaScriptEnabled(true);
            web.loadUrl(webURL);
            web.setPadding(0, 0, 0, 0);
            web.getSettings().setLoadWithOverviewMode(true);
            web.getSettings().setUseWideViewPort(true);
            web.getSettings().setSupportZoom(true);
            web.getSettings().setBuiltInZoomControls(true);
            
            web.setWebViewClient(new HelloWebViewClient());
        }
    
        @Override
        public boolean onCreateOptionsMenu(Menu menu) {
            getMenuInflater().inflate(R.menu.activity_main, menu);
            return true;
        }
        
        private class HelloWebViewClient extends WebViewClient {
        	public boolean shouldOverrideUrlLoading(WebView web, String url) {
        		web.loadUrl(url);
        		return true;
        	}
        }
        
        public boolean onKeyDown(int keyCode, KeyEvent event) {
        	if ((keyCode == KeyEvent.KEYCODE_BACK) &amp;&amp; web.canGoBack()) {
        		web.goBack();
        		return true;
        	}
        	return super.onKeyDown(keyCode, event);
        }
        
    }

***AndroidManifest.xml***

    &lt;manifest xmlns:android=&quot;http://schemas.android.com/apk/res/android&quot;
        package=&quot;com.mark.myapp&quot;
        android:versionCode=&quot;1&quot;
        android:versionName=&quot;1.0&quot; &gt;
    
        &lt;uses-sdk
            android:minSdkVersion=&quot;8&quot;
            android:targetSdkVersion=&quot;15&quot; /&gt;
    
        &lt;application
            android:icon=&quot;@drawable/ic_launcher&quot;
            android:label=&quot;@string/app_name&quot;
            android:theme=&quot;@style/AppTheme&quot; &gt;
            &lt;activity
                android:name=&quot;.MainActivity&quot;
               
              	android:configChanges=&quot;orientation|keyboardHidden&quot;&gt;
                &lt;intent-filter&gt;
                    &lt;action android:name=&quot;android.intent.action.MAIN&quot; /&gt;
    
                    &lt;category android:name=&quot;android.intent.category.LAUNCHER&quot; /&gt;
                &lt;/intent-filter&gt;
            &lt;/activity&gt;
        &lt;/application&gt;
    	&lt;uses-permission android:name=&quot;android.permission.INTERNET&quot;/&gt;
    &lt;/manifest&gt;

Android - Preventing WebView reload on Rotate

I make this call to a static singleton instance from the class `GameManager.java`.

    HUD.getInstance().update(timeDelta);

`HUD.java` contains the `HUD` class as well as two other related classes, `HUDTextElement` and `HUDElement`. All the classes are in the same root path `../src/org/mypackage`.

However, when compiling this project in IntelliJ I get **cannot find Symbol HUD** on the line I make the `HUD.getInstance()` call.

This exact same code compiles just fine in Eclipse, any idea what the problem is?

Getting &quot;cannot find Symbol&quot; in Java project in IntelliJ

I have the Android SDK installed on both a Linux machine using open SuSE 12.1. I&#39;ve used both machines to successfully build Android apps many times and sign them both with a debug key for testing and a release key from my own keystore, so it should be somewhere on each machine.

Using the command

    jarsigner

Returns a command not found error on both machines, however. I&#39;ve looked in the Android SDK folder, JDK folder on Windows, and /usr/lib64/jvm/ but it&#39;s not anywhere I&#39;ve looked.

I assume it must be under a different name. I&#39;ve also run:

     find -name jarsigner

over the whole system on the Linux box with no success.

Where is jarsigner?

I have a Sonar profile in Maven. Everything works fine except the code coverage metric. I want to make Sonar ignore some classes only for the code coverage metric. I have the following profile:

&lt;!-- language-all: xml --&gt;

    &lt;profile&gt;
        &lt;id&gt;sonar&lt;/id&gt;
        &lt;properties&gt;
            &lt;sonar.exclusions&gt;**/beans/jaxb/**&lt;/sonar.exclusions&gt;
        &lt;/properties&gt;
        &lt;build&gt;
            &lt;plugins&gt;
                &lt;plugin&gt;
                    &lt;groupId&gt;org.apache.maven.plugins&lt;/groupId&gt;
                    &lt;artifactId&gt;maven-surefire-plugin&lt;/artifactId&gt;
                    &lt;version&gt;${maven.surefire.plugin.version}&lt;/version&gt;
                    &lt;configuration&gt;
                        &lt;redirectTestOutputToFile&gt;true&lt;/redirectTestOutputToFile&gt;
                        &lt;excludes&gt;
                            &lt;exclude&gt;**/*Suite*.java&lt;/exclude&gt;
                            &lt;exclude&gt;**/*RemoteTest.java&lt;/exclude&gt;
                            &lt;exclude&gt;**/*SpringTest.java&lt;/exclude&gt;
                            &lt;exclude&gt;**/*CamelTest.java&lt;/exclude&gt;
                            &lt;exclude&gt;**/*FunctionalTest.java&lt;/exclude&gt;
                            &lt;exclude&gt;**/*IntegrationTest.java&lt;/exclude&gt;
                            &lt;exclude&gt;**/*DaoBeanTest.java&lt;/exclude&gt;
                        &lt;/excludes&gt;
                    &lt;/configuration&gt;
                &lt;/plugin&gt;                    
            &lt;/plugins&gt;
        &lt;/build&gt;
    &lt;/profile&gt;

Please help. I tried to add something like 

    &lt;exclude&gt;com/qwerty/dw/publisher/Main.class&lt;/exclude&gt;

but it didn&#39;t help

**UPDATE**

I have a correct Cobertura profile. I tried to add it to the Sonar profile, but still I have 53% instead about 95% like in the Cobertura profile

    &lt;profile&gt;
        &lt;id&gt;sonar&lt;/id&gt;
        &lt;properties&gt;
            &lt;sonar.exclusions&gt;**/beans/jaxb/**&lt;/sonar.exclusions&gt;
            &lt;sonar.core.codeCoveragePlugin&gt;cobertura&lt;/sonar.core.codeCoveragePlugin&gt;
        &lt;/properties&gt;
        &lt;build&gt;
            &lt;plugins&gt;
                &lt;plugin&gt;
                    &lt;groupId&gt;org.apache.maven.plugins&lt;/groupId&gt;
                    &lt;artifactId&gt;maven-surefire-plugin&lt;/artifactId&gt;
                    &lt;version&gt;${maven.surefire.plugin.version}&lt;/version&gt;
                    &lt;configuration&gt;
                        &lt;redirectTestOutputToFile&gt;true&lt;/redirectTestOutputToFile&gt;
                        &lt;excludes&gt;
                            &lt;exclude&gt;**/*Suite*.java&lt;/exclude&gt;
                            &lt;exclude&gt;**/*RemoteTest.java&lt;/exclude&gt;
                            &lt;exclude&gt;**/*SpringTest.java&lt;/exclude&gt;
                            &lt;exclude&gt;**/*CamelTest.java&lt;/exclude&gt;
                            &lt;exclude&gt;**/*FunctionalTest.java&lt;/exclude&gt;
                            &lt;exclude&gt;**/*IntegrationTest.java&lt;/exclude&gt;
                            &lt;exclude&gt;**/*DaoBeanTest.java&lt;/exclude&gt;
                        &lt;/excludes&gt;
                    &lt;/configuration&gt;
                &lt;/plugin&gt;
                &lt;plugin&gt;
                    &lt;groupId&gt;org.codehaus.mojo&lt;/groupId&gt;
                    &lt;artifactId&gt;cobertura-maven-plugin&lt;/artifactId&gt;
                    &lt;version&gt;${cobertura.maven.plugin.version}&lt;/version&gt;
                    &lt;configuration&gt;
                        &lt;instrumentation&gt;
                            &lt;excludes&gt;
                                &lt;exclude&gt;com/qwerty/dw/dao/*&lt;/exclude&gt;
                                &lt;exclude&gt;com/qwerty/dw/domain/*&lt;/exclude&gt;
                                &lt;exclude&gt;com/qwerty/dw/beans/**/*&lt;/exclude&gt;
                                &lt;exclude&gt;com/qwerty/dw/daemon/exception/*&lt;/exclude&gt;
                                &lt;exclude&gt;com/qwerty/dw/daemon/Main.class&lt;/exclude&gt;
                                &lt;exclude&gt;com/qwerty/dw/sink/Main.class&lt;/exclude&gt;
                                &lt;exclude&gt;com/qwerty/dw/publisher/Main.class&lt;/exclude&gt;
                                &lt;exclude&gt;com/qwerty/dw/publisher/dao/*&lt;/exclude&gt;
                                &lt;exclude&gt;com/qwerty/dw/publisher/domain/*&lt;/exclude&gt;
                            &lt;/excludes&gt;
                        &lt;/instrumentation&gt;
                        &lt;formats&gt;
                            &lt;format&gt;html&lt;/format&gt;
                        &lt;/formats&gt;
                        &lt;aggregate&gt;true&lt;/aggregate&gt;
                        &lt;check&gt;
                            &lt;haltOnFailure&gt;true&lt;/haltOnFailure&gt;
                            &lt;branchRate&gt;60&lt;/branchRate&gt;
                            &lt;lineRate&gt;60&lt;/lineRate&gt;
                            &lt;totalBranchRate&gt;60&lt;/totalBranchRate&gt;
                            &lt;totalLineRate&gt;60&lt;/totalLineRate&gt;
                        &lt;/check&gt;
                    &lt;/configuration&gt;
                    &lt;executions&gt;
                        &lt;execution&gt;
                            &lt;goals&gt;
                                &lt;goal&gt;clean&lt;/goal&gt;
                                &lt;goal&gt;check&lt;/goal&gt;
                            &lt;/goals&gt;
                        &lt;/execution&gt;
                    &lt;/executions&gt;
                &lt;/plugin&gt;
            &lt;/plugins&gt;
        &lt;/build&gt;
    &lt;/profile&gt;

How to make Sonar ignore some classes for codeCoverage metric?

I&#39;m trying to only show something based on if a string is not equal to:


    &lt;c:if test=&quot;${content.getContentType().getName() != &quot;MCE&quot;}&quot;&gt;
    &lt;li&gt;&lt;a href=&quot;#publish-history&quot; id=&quot;publishHistoryTab&quot;&gt;Publish History&lt;/a&gt;&lt;/li&gt;
    &lt;/c:if&gt;

It keeps throwing the error `org.apache.jasper.JasperException: /WEB-INF/jsp/content/manage.jsp(14,60) PWC6212: equal symbol expected`

I&#39;ve also tried `not eq` instead of `!=`

What is the valid syntax for `not equal to`?

How do I compare if a string is not equal to?

According to the JLS, an `int` array should be filled by zeros just after initialization. However, I am faced with a situation where it is not. Such a behavior occurs first in JDK 7u4 and also occurs in all later updates (I use 64-bit implementation). The following code throws exception:

    public static void main(String[] args) {
            int[] a;
            int n = 0;
            for (int i = 0; i &lt; 100000000; ++i) {
                a = new int[10];
                for (int f : a)
                    if (f != 0)
                      throw new RuntimeException(&quot;Array just after allocation: &quot;+ Arrays.toString(a));
                Arrays.fill(a, 0);
                for (int j = 0; j &lt; a.length; ++j)
                    a[j] = (n - j)*i;
                for (int f : a)
                    n += f;
            }
            System.out.println(n);
        }

The exception occurs after the JVM performs compilation of the code block and does not arise with `-Xint` flag. Additionally, the `Arrays.fill(...)` statement (as all other statements in this code) is necessary, and the exception does not occurs if it is absent. It is clear that this possible bug is bounded with some JVM optimization. Any ideas for the reason of such a behavior?

*Update:*  
I see this behavior on HotSpot 64-bit server VM, Java version from 1.7.0_04 to 1.7.0_10 on Gentoo Linux, Debian Linux (both kernel 3.0 version) and MacOS Lion. This error can always be reproduced with the code above. I did not test this problem with a 32-bit JDK or on Windows. I already sent a bug report to the Oracle (bug id 7196857) and it will appear in public Oracle bug database in few days.


*Update:*    
Oracle published this bug at their public bug database: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7196857 

Java: int array initializes with nonzero elements

There is a relatively-new lightweight JVM called [Avian][1] that can produce executables for iOS targets.

There isn&#39;t too much documentation on the website (and not much can be found searching with Google). I was wondering if anybody was aware of a step-by-step tutorial on how to get a basic Scala program running on iOS, using [Avian][1].


  [1]: http://oss.readytalk.com/avian/

Scala on iOS using Avian

There are three opcodes to invoke Java methods. It is clear that invokeStatic is just for static method invocation.

As far as I know invokespecial is used when invoking constructor and private methods. So, do we need to differenticate private and public method invocation at run time? It could be invoked with same opcode say invokevirtual?

Does JVM deals with private and public method definition? As far as I know  public and private keywords is just needed at development phase for encapsulation?


Why invokeSpecial is needed when invokeVirtual exists

Please explain the use of the `Xms` and `Xmx` parameters in JVMs. What are the default values for them?



What are the -Xms and -Xmx parameters when starting JVM?

Some say I need to do that in Run Configurations for my application. When I open that window, could you please tell me how to set the right argument and the amount of memory? Say how to set 2GB or 1.5GB?

How to increase application heap size in Eclipse?

&gt; **Possible Duplicate:**  
&gt; [What and where are the stack and heap?](https://stackoverflow.com/questions/79923/what-and-where-are-the-stack-and-heap)  

&lt;!-- End of automatically inserted text --&gt;

With regard to the basic concepts of memory layout in a c program, I understand the that:

 - The language uses two primary data structures **stack** and **heap**. 
 - Stack is created to store the local variables and book keeping data of subroutines 
 - Heap is created to store the dynamically allocated variables of the program
 - Heap is of variable length in nature.(Not very sure on stack) 
 - Normally it is the responsibility of the compiler/Language to request the OS to create these data structures before the execution.

### Questions ###

 - What is the initial size with which a stack/heap is created? and who decides it?
 - Wherein physical memory are they are created? I see a general description as ***&quot;Stack is created  in the top-level-address and the heap at the low-level-address&quot;*** Please elobarate this 

 



Size of stack and heap memory

How can I check Heap Size (and Used Memory) of a Java Application on Linux through the command line?

I have tried through jmap. But it gives info. about internal memory areas like Eden/ PermGen etc., which is not useful to me. 

I am looking for something like:

 - Max Memory: 1GB
 - Min Memory: 256 MB
 - Heap Memory: 700 MB
 - Used Memory: 460 MB

That&#39;s all. I know that I can see this in JConsole etc., but I need to do it via command-line. (can&#39;t enable JMX etc.)

How to find Java Heap Size and Memory Used (Linux)?

My Jenkins jobs are running out of memory, giving `java.lang.OutOfMemoryError` messages in the build log. But I used the Ubuntu Package Manager, `aptitude`, or `apt-get` to install Jenkins, and I don&#39;t know where to look to change the amount of heap space allocated to Jenkins.

How do I give Jenkins more heap space when it&#39;s running as a daemon on Ubuntu?

I&#39;m studying computer engineering, and I have some electronics courses. I heard, from two of my professors (of these courses) that it is possible to avoid using the `free()` function (after `malloc()`, `calloc()`, etc.) because the memory spaces allocated likely won&#39;t be used again to allocate other memory. That is, for example, if you allocate 4 bytes and then release them you will have 4 bytes of space that likely won&#39;t be allocated again: you will have a *hole*.

I think that&#39;s crazy: you can&#39;t have a *not-toy-program* where you allocate memory on the heap without releasing it. But I don&#39;t have the knowledge to explain exactly why it&#39;s so important that for each `malloc()` there must be a `free()`.

So: are there ever circumstances in which it might be appropriate to use a `malloc()` without using `free()`? And if not, how can I explain this to my professors?

Is it ever OK to *not* use free() on allocated memory?

Can I check heap usage of a running JVM from the commandline, I mean the actual usage rather than the max amount allocated with Xmx.

I need it to be commandline because I don&#39;t have access to a windowing environment, and I want script based on the value , the application is running in Jetty Application server 

How to check heap usage of a running JVM from the command line?

Other than the more &#39;advanced&#39; GUI from Java mission control, how are they different?

At first glance they seem to offer very similar functionality (Interpreting JMX data and Memory/CPU profiling).

However, as they are both shipped with the JDK (I&#39;m using JDK 1.7.0_51 SE) I&#39;m assuming there are significant differences, otherwise they would be combined into a single solution. Especially as this increases the size of the JDK significantly.

Is Java Mission Control ultimately going to replace JVisualVM in the future?

What are the differences between JVisualVM and Java Mission Control?

Can someone please explain me the difference between `Sleeping`, `Wait`, `Park`, and `Monitor` thread states in VisualVM.

![enter image description here][1]

This is what I have found:

`Running`: thread is still running. &lt;br /&gt;
`Sleeping`: thread is sleeping (method yield() was called on the thread object)&lt;br /&gt;
`Wait`: thread was blocked by a mutex or a barrier, and is waiting for another thread to release the lock&lt;br /&gt;
`Park`: parked threads are suspended until they are given a permit. Unparking a thread is usually done by calling method unpark() on the thread object&lt;br /&gt;
`Monitor`: threads are waiting on a condition to become true to resume execution

What I am unable to understand is the state Park, what actually suspends the thread? How do I detect in the code what has made the thread suspend its execution?

Can someone please guide me in this regard.

Thanks.


  [1]: http://i.stack.imgur.com/4WYvV.png

Content Type	Original Author	Original Content on Stackoverflow
Question	Parag	View Question on Stackoverflow
Solution 1 - Java	npe	View Answer on Stackoverflow

Difference between sampling and profiling in jVisualVM

Java Problem Overview

Java Solutions

Solution 1 - Java

Heroku "psql: FATAL: remaining connection slots are reserved for non-replication superuser connections"

How do I terminate a thread in C++11?

Attributions