Open a terminal and type: `java -version`, or `javac -version`.

If you have all the latest updates for Snow Leopard, you should be running JDK 1.6.0_20 at this moment (the same as Oracle&#39;s current JDK version).

In `/System/Library/Frameworks/JavaVM.framework/Versions` you&#39;ll see all the installed JDKs. There is a symbolic link named `CurrentJDK` pointing the active JDK.

The simplest solution would be
open terminal

    $ java -version

it shows the following

    java version &quot;1.6.0_65&quot;


2. Stefan&#39;s solution also works for me. Here&#39;s the exact input:


`$ cd /System/Library/Frameworks/JavaVM.framework/Versions`

`$ ls -l`

Below is the last line of output:

    lrwxr-xr-x   1 root  wheel   59 Feb 12 14:57 CurrentJDK -&gt; /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents

1.6.0.jdk would be the answer

On modern macOS, the correct path is `/Library/Java/JavaVirtualMachines`.

You can also avail yourself of the command `/usr/libexec/java_home`, which will scan that directory for you and return a list.

Which SDKs? If you mean the SDK for Cocoa development, you can check in `/Developer/SDKs/` to see which ones you have installed.

If you&#39;re looking for the *Java* SDK version, then open up `/Applications/Utilities/Java Preferences`. The versions of Java that you have installed are listed there.

On Mac OS X 10.6, though, the only Java version is 1.6.

Run this command in your terminal:

    $ java -version

    java version &quot;1.8.0_181&quot;
    Java(TM) SE Runtime Environment (build 1.8.0_181-b13)
    Java HotSpot(TM) 64-Bit Server VM (build 25.181-b13, mixed mode)
    Cristians-MacBook-Air:~ fa$ 




Every time I start a hard problem and if can not figure out the exact solution or can not get started, I get into this never ending discussion with myself, as below:

 - That problem
   solving/mathematics/algorithms skills
   are gifted  (not that you can learn
   by practicing, by practice, you only
   master the kind of problems that you
   already have solved before) 
   
   
 - only those who went to good schools  can do it, as they learned it early.

What are your thoughts, can one achieve awesomeness in problem solving/algorithms just by hard work or you need to have that extra-gene in you?

Problem solving/ Algorithm Skill is a knack or can be developed with practice?

I have an object (basically a VO) in Java and I don&#39;t know its type.  
I need to get values which are not null in that object. 

How can this be done?

How to get the fields in an Object via reflection?

I have a MacBook Pro running Snow Leopard;  how can I see what version of the Java SDK is installed on my Mac?

Determining the version of Java SDK on the Mac

<p>I have a MacBook Pro running Snow Leopard;  how can I see what version of the Java SDK is installed on my Mac?</p>


Having dealt with yet another stupid eclipse problem, I want to try to get the lightest, most minimal Eclipse installation as possible.

To be clear, I use eclipse for two things:

 - Editing Java
 - Debugging Java

Everything else I do through Emacs/Zsh (editing JSP/XML/JS, file management, SVN check-in, etc). I have not found any aspect of working in Eclipse to do these tasks to be efficient or even reliable, so I do not want plug-ins that relate to it.

From the eclipse.org site, [this](http://www.eclipse.org/downloads/packages/eclipse-ide-java-developers/galileosr2) is the lightest install of eclipse that they have, and I don&#39;t want any of those things (Bugzilla, Mylyn, CVS xml_ui), and have actually had problems with each of them even though I do not use them.

So what is the minimal build I can get that will:

1. Ignore SVN metadata
2. Includes the full-featured editor (intellisense and type-finding)
3. Includes the full-featured debugger (standard Eclipse/JDK)

Does not have any extra plug-ins, platforms, or &quot;integrations&quot; with other platforms, specifically, I don&#39;t want to deal with plug-ins relating to:

Maven, JSP Validation, Javascript editing or validation, CVS or SVN, Mylyn, Spring or Hibernate &quot;natures&quot;, app servers like a bundled Tomcat/GlassFish/etc, J2EE tools, or anything of the like.

I do primarily Spring/Hibernate/web-mvc apps, and have never dealt with an Eclipse plug-in that handles any of it gracefully, I can work effectively with my own toolset, but Eclipse extensions do nothing but get in the way.

I have worked with plain eclipse up to Ganymede, MyEclipse (up to 7.5), and the latest version of Spring-SourceTools, and find that they are all saddled with buggy useless plug-ins (though the combination is always different). 

Switching to NetBeans/Intellij is not an option, and my teammates work with SVN-controlled .class/.project files, so it pretty much has to be Eclipse.

Does anyone have any good advice on how I can save a few grey hairs?


Getting a lightweight installation of Java Eclipse

What are the best practices if you have a class which accepts some parameters but none of them are allowed to be `null`?

The following is obvious but the exception is a little unspecific:

    public class SomeClass
    {
         public SomeClass(Object one, Object two)
         {
            if (one == null || two == null)
            {
                throw new IllegalArgumentException(&quot;Parameters can&#39;t be null&quot;);
            }
            //...
         }
    }

Here the exceptions let you know which parameter is null, but the constructor is now pretty ugly:

    public class SomeClass
    {
         public SomeClass(Object one, Object two)
         {
            if (one == null)
            {
                throw new IllegalArgumentException(&quot;one can&#39;t be null&quot;);
            }           
            if (two == null)
            {
                throw new IllegalArgumentException(&quot;two can&#39;t be null&quot;);
            }
            //...
      }

Here the constructor is neater, but now the constructor code isn&#39;t really in the constructor:

    public class SomeClass
    {
         public SomeClass(Object one, Object two)
         {
            setOne(one);
            setTwo(two);
         }


         public void setOne(Object one)
         {
            if (one == null)
            {
                throw new IllegalArgumentException(&quot;one can&#39;t be null&quot;);
            }           
            //...
         }

         public void setTwo(Object two)
         {
            if (two == null)
            {
                throw new IllegalArgumentException(&quot;two can&#39;t be null&quot;);
            }
            //...
         }
      }

Which of these styles is best? 

Or is there an alternative which is more widely accepted?

Java constructor style: check parameters aren&#39;t null

I would like to make BIT (Built in tests) to a number of server in my cloud. I need the request to fail on large timeout.

How should I do this with java?

Trying something like the below does not seem to work.

    public class TestNodeAliveness {
     public static NodeStatus nodeBIT(String elasticIP) throws ClientProtocolException, IOException {
      HttpClient client = new DefaultHttpClient();
      client.getParams().setIntParameter(&quot;http.connection.timeout&quot;, 1);
      
      HttpUriRequest request = new HttpGet(&quot;http://192.168.20.43&quot;);
      HttpResponse response = client.execute(request);
      
      System.out.println(response.toString());
      return null;
     }
     
     
     public static void main(String[] args) throws ClientProtocolException, IOException {
      nodeBIT(&quot;&quot;);
     }
    }

-- EDIT: Clarify what library is being used --

I&#39;m using httpclient from apache, here is the relevant pom.xml section

 

     &lt;dependency&gt;
       &lt;groupId&gt;org.apache.httpcomponents&lt;/groupId&gt;
       &lt;artifactId&gt;httpclient&lt;/artifactId&gt;
       &lt;version&gt;4.0.1&lt;/version&gt;
       &lt;type&gt;jar&lt;/type&gt;
     &lt;/dependency&gt;



Java HTTP Client Request with defined timeout

How does Java handle integer underflows and overflows?

Leading on from that, how would you check/test that this is occurring?

How does Java handle integer underflows and overflows and how would you check for it?

I am working with tomcat 6.0, and while I am indexing (not while i am starting tomcat), I have a permgen space error.      
How could I increase that space??

Thanks

Increase permgen space

OS X lacks linux&#39;s `strace`, but it has `dtrace` which is supposed to be so much better. 

However, I miss the ability to do simple tracing on individual commands. For example, on linux I can write `strace -f gcc hello.c ` to caputre all system calls, which gives me the  list of *all* the filenames needed by the compiler to compile my program (the excellent [memoize][1] script is built upon this trick)

  [1]: http://www.eecs.berkeley.edu/~billm/memoize.html

I want to port memoize on the mac, so I need some kind of `strace`. What I actually need is the list of files `gcc` reads and writes into, so what I need is more of a `truss`. Sure enough can I say `dtruss -f gcc hello.c` and get somewhat the same functionality, but then the compiler is run with root priviledges, which is obviously undesirable (apart from the massive security risk, one issue is that the `a.out` file is now owned by root :-)

I then tried `dtruss -f sudo -u myusername gcc hello.c`, but this feels a bit wrong, and does not work anyway (I get no `a.out` file at all this time, not sure why)

All that long story tries to motivate my original question: **how do I get `dtrace` to run my command with normal user privileges, just like `strace` does in linux ?**

Edit: is seems that I&#39;m not the only one wondering how to do this: question [#1204256][2] is pretty much the same as mine (and has the same suboptimal sudo answer :-) 

[2]: https://stackoverflow.com/questions/1204256/how-to-trace-a-program-from-its-very-beginning-without-running-it-as-root


How can I get dtrace to run the traced command with non-root priviledges?

While I found similar [question][1] I didn&#39;t find an answer to my problem

When I try to rename the directory from FOO to foo via `git mv FOO foo` I get  

    fatal: renaming &#39;FOO&#39; failed: Invalid argument

OK. So I try `git mv FOO foo2 &amp;&amp; git mv foo2 foo`

But when I try to commit via `git commit .` I get

    # On branch master
    # Untracked files:
    #   (use &quot;git add &lt;file&gt;...&quot; to include in what will be committed)
    #
    # foo
    nothing added to commit but untracked files present (use &quot;git add&quot; to track)

When I add the directory via `git add foo` nothing changes and `git commit .` gives me the same message again. 

What am I doing wrong? I thought I&#39;m using a case-sensitive system (OSX) why can&#39;t I simply rename the directory?


  [1]: https://stackoverflow.com/questions/1596653/how-to-change-case-of-a-file-in-git-under-cygwin

git mv and only change case of directory

How can I save a NSImage as a new file (png, jpg, ...) in a certain directory?


How to save a NSImage as a new file

I&#39;m trying to link a `UILabel` with an `IBOutlet` created in my class.

My application is crashing with the following error. 

What does this mean? 

How can I fix it?

&gt; *** Terminating app due to uncaught exception &#39;NSUnknownKeyException&#39;, reason: &#39;[&amp;lt;UIViewController 0x6e36ae0&gt; setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key XXX.&#39;


Xcode - How to fix &#39;NSUnknownKeyException&#39;, reason: … this class is not key value coding-compliant for the key X&quot; error?

I just want that Mac OS X 10.6 does a hardware beep sound like in open suse and other distributions. I tried following approaches

Terminal -&gt; beep = -bash: beep: command not found

Terminal -&gt; say beep = voice speaks out beep (Not a Hardware beep but awesome ;) )

applescript -&gt; beep = Macintosh bell (I want a Hardware beep!)

Does anybody know how to make the Hardware beep in bin/bash or applescript?

Content Type	Original Author	Original Content on Stackoverflow
Question	Ali_IT	View Question on Stackoverflow
Solution 1 - Java	Jesper	View Answer on Stackoverflow
Solution 2 - Java	Stefan Schmidt	View Answer on Stackoverflow
Solution 3 - Java	Rae	View Answer on Stackoverflow
Solution 4 - Java	Tim Keating	View Answer on Stackoverflow
Solution 5 - Java	mipadi	View Answer on Stackoverflow
Solution 6 - Java	Jose Leonardo Rosero	View Answer on Stackoverflow

Determining the version of Java SDK on the Mac

Java Problem Overview

Java Solutions

Solution 1 - Java

Solution 2 - Java

Solution 3 - Java

Solution 4 - Java

Solution 5 - Java

Solution 6 - Java

How to get the fields in an Object via reflection?

Problem solving/ Algorithm Skill is a knack or can be developed with practice?

Attributions