To get the currently logged in user:

    System.getProperty(&quot;user.name&quot;); //platform independent 

and the hostname of the machine:

    java.net.InetAddress localMachine = java.net.InetAddress.getLocalHost();
    System.out.println(&quot;Hostname of local machine: &quot; + localMachine.getHostName());


To get the currently logged in user:

    System.getProperty(&quot;user.name&quot;);

To get the host name of the machine:

    InetAddress.getLocalHost().getHostName();

To answer the last part of your question, the [Java API][1] says that getHostName() will return

&gt; the host name for this IP address, or if the operation is not allowed by the security check, the textual representation of the IP address.


  [1]: http://docs.oracle.com/javase/6/docs/api/java/net/InetAddress.html#getHostName%28%29

Using `user.name` is not secure as environment variables can be faked. Method you were using is good, there are similar methods for unix based OS as well

To get the currently logged in user path:

    System.getProperty(&quot;user.home&quot;);

I know there&#39;s no single hard-and-fast answer, but is there a generic &lt;strike&gt;order-of-magnitude estimate&lt;/strike&gt; approximation for the encryption overhead of SSL versus unencrypted socket communication? I&#39;m talking only about the comm processing and wire time, not counting application-level processing.

**Update**

There is [a question about HTTPS versus HTTP][1], but I&#39;m interested in looking lower in the stack.

(I replaced the phrase &quot;order of magnitude&quot; to avoid confusion; I was using it as informal jargon rather than in the formal CompSci sense. Of course if I *had* meant it formally, as a true geek I would have been thinking binary rather than decimal! ;-)

**Update**

Per request in comment, assume we&#39;re talking about good-sized messages (range of 1k-10k) over persistent connections. So connection set-up and packet overhead are not significant issues.


  [1]: https://stackoverflow.com/questions/149274/http-vs-https-performance

How much overhead does SSL impose?

If I have several classes with functions that I need but want to store separately for organisation, can I extend a class to have both?

i.e. `class a extends b extends c`

edit: I know how to extend classes one at a time, but I&#39;m looking for a method to instantly extend a class using multiple base classes - AFAIK you can&#39;t do this in PHP but there should be ways around it without resorting to `class c extends b`, `class b extends a`

Can I extend a class using more than 1 class in PHP?

Is it possible to get the name of the currently logged in user (Windows/Unix) and the hostname of the machine?

I assume it&#39;s just a property of some static environment class.

I&#39;ve found this for the user name

    com.sun.security.auth.module.NTSystem NTSystem = new
            com.sun.security.auth.module.NTSystem();
    System.out.println(NTSystem.getName());

and this for the machine name:

    import java.net.InetAddress;
    ...
    String computerName;
    ...
    try {
        computerName = InetAddress.getLocalHost().getHostName();
    }
    
    catch(Exception ex) {
        ...
    }

Is the first one just for Windows?

And what will the second one do, if you don&#39;t have a hostname set?


Java current machine name and logged in user?

Is it possible to get the name of the currently logged in user (Windows/Unix) and the hostname of the machine?
I assume it's just a property of some static environment class.
I've found this for the user name
<pre><code class="hljs language-ini">com.sun.security.auth.module.NTSystem NTSystem = new
 com.sun.security.auth.module.NTSystem();
System.out.println(NTSystem.getName());
</code></pre>
and this for the machine name:
<pre><code class="hljs language-ini">import java.net.InetAddress;
...
String computerName;
...
try {
 computerName = InetAddress.getLocalHost().getHostName();
}

catch(Exception ex) {
 ...
}
</code></pre>
Is the first one just for Windows?
And what will the second one do, if you don't have a hostname set?

I&#39;m trying to work with [fractions][1] in Java. 

I want to implement arithmetic functions.  For this, I will first require a way to normalize the functions.  I know I can&#39;t add 1/6 and 1/2 until I have a common denominator. I will have to add 1/6 and 3/6.  A naive approach would have me add 2/12 and 6/12 and then reduce.  How can I achieve a common denominator with the least performance penalty?  What algorithm is best for this?

----------

Version 8 (thanks to [hstoerr][2]):

&gt; Improvements include:
&gt; 
&gt;  - the equals() method is now consistent with the compareTo() method

    final class Fraction extends Number {
        private int numerator;
        private int denominator;

        public Fraction(int numerator, int denominator) {
            if(denominator == 0) {
                throw new IllegalArgumentException(&quot;denominator is zero&quot;);
            }
            if(denominator &lt; 0) {
                numerator *= -1;
                denominator *= -1;
            }
            this.numerator = numerator;
            this.denominator = denominator;
        }
    
        public Fraction(int numerator) {
            this.numerator = numerator;
            this.denominator = 1;
        }
    
        public int getNumerator() {
            return this.numerator;
        }
    
        public int getDenominator() {
            return this.denominator;
        }
    
        public byte byteValue() {
            return (byte) this.doubleValue();
        }
    
        public double doubleValue() {
            return ((double) numerator)/((double) denominator);
        }
    
        public float floatValue() {
            return (float) this.doubleValue();
        }
    
        public int intValue() {
            return (int) this.doubleValue();
        }
    
        public long longValue() {
            return (long) this.doubleValue();
        }
    
        public short shortValue() {
            return (short) this.doubleValue();
        }

        public boolean equals(Fraction frac) {
            return this.compareTo(frac) == 0;
        }
    
        public int compareTo(Fraction frac) {
            long t = this.getNumerator() * frac.getDenominator();
            long f = frac.getNumerator() * this.getDenominator();
            int result = 0;
            if(t&gt;f) {
                result = 1;
            }
            else if(f&gt;t) {
                result = -1;
            }
            return result;
        }
    }

----------

I have removed all previous versions.  My thanks to:

 - [Dave Ray][3]
 - [cletus][4]
 - [duffymo][5]
 - [James][6]
 - [Milhous][7]
 - [Oscar Reyes][8]
 - [Jason S][9]
 - [Francisco Canedo][10]
 - [Outlaw Programmer][11]
 - [Beska][12]


  [1]: http://en.wikipedia.org/wiki/Fraction_%28mathematics%29#Vulgar.2C_proper.2C_and_improper_fractions
  [2]: https://stackoverflow.com/users/21499/hstoerr
  [3]: https://stackoverflow.com/users/40310/dave-ray
  [4]: https://stackoverflow.com/users/18393/cletus
  [5]: https://stackoverflow.com/users/37213/duffymo
  [6]: https://stackoverflow.com/users/41039/james
  [7]: https://stackoverflow.com/users/17712/milhous
  [8]: https://stackoverflow.com/users/20654/oscar-reyes
  [9]: https://stackoverflow.com/users/44330/jason-s
  [10]: https://stackoverflow.com/users/54591/francisco-canedo
  [11]: https://stackoverflow.com/users/1471/outlaw-programmer
  [12]: https://stackoverflow.com/users/57120/beska


Best way to represent a fraction in Java?

Is there a way in Java&#39;s for-each loop

    for(String s : stringArray) {
      doSomethingWith(s);
    }

to find out how often the loop has already been processed?

Aside from using the old and well-known `for(int i=0; i &lt; boundary; i++)` - loop, is the construct

    int i = 0;
    for(String s : stringArray) {
      doSomethingWith(s);
      i++;
    }

the only way to have such a counter available in a for-each loop?

Is there a way to access an iteration-counter in Java&#39;s for-each loop?

I have a question about the primitive type `short` in Java. I am using JDK 1.6. 

If I have the following: 

    short a = 2;
    short b = 3;
    short c = a + b;

the compiler does not want to compile - it says that it &quot;cannot convert from int to short&quot; and suggests that I make a cast to `short`, so this:

    short c = (short) (a + b);

really works. But my question is why do I need to cast? The values of a and b are in the range of `short` - the range of short values is {-32,768, 32767}.
I also need to cast when I want to perform the operations -, *, / (I haven&#39;t checked for others).

If I do the same for primitive type `int`, I do not need to cast aa+bb to `int`. The following works fine:

    int aa = 2;
    int bb = 3;
    int cc = aa +bb;

I discovered this while designing a class where I needed to add two variables of type short, and the compiler wanted me to make a cast. If I do this with two variables of type `int`, I don&#39;t need to cast. 

A small remark: the same thing also happens with the primitive type `byte`. So, this works:

    byte a = 2;
    byte b = 3;
    byte c = (byte) (a + b);

but this not:

    byte a = 2;
    byte b = 3;
    byte c = a + b;

For `long`, `float`, `double`, and `int`, there is no need to cast. Only for `short` and `byte` values. 

Primitive type &#39;short&#39; - casting in Java

It is possible to add and remove elements from an enum in Java at runtime?

For example, could I read in the labels and constructor arguments of an enum from a file?

----

@saua, it&#39;s just a question of whether it can be done out of interest really. I was hoping there&#39;d be some neat way of altering the running bytecode, maybe using [BCEL][1] or something. I&#39;ve also followed up with [this question][2] because I realised I wasn&#39;t totally sure when an enum should be used.

I&#39;m pretty convinced that the right answer would be to use a collection that ensured uniqueness instead of an enum if I want to be able to alter the contents safely at runtime.


  [1]: http://bcel.sourceforge.net/
  [2]: https://stackoverflow.com/questions/481068/when-to-use-enum-or-collection-in-java

Can I add and remove elements of enumeration at runtime in Java

I&#39;m putting together a quick and dirty animation using swing.  I would like the window to be maximized.  How can I do that?

JFrame Maximize window

I need to create one config option for my Rails application. It can be the same for all environments. I found that if I set it in `environment.rb`, it&#39;s available in my views, which is exactly what I want...

    environment.rb

    AUDIOCAST_URI_FORMAT = http://blablalba/blabbitybla/yadda

Works great.

However, I&#39;m a little uneasy. Is this a good way to do it? Is there a way that&#39;s more hip?

Best way to create custom config options for my Rails app?

In Windows environment there is an API to obtain the path which is running a process. Is there something similar in Unix / Linux?

Or is there some other way to do that in these environments?


How do I get the path of a process in Unix / Linux

Using a **Linux shell**, how do I start a program with a different working directory from the current working directory?

For example, I have a binary file `helloworld` that creates the file `hello-world.txt` in the **current directory**. 
&lt;br&gt;&lt;br&gt;
This file is inside of directory `/a`. 

Currently, I am in the directory `/b`. I want to start my program running `../a/helloworld` and get the `hello-world.txt` somewhere in a third directory `/c`.

How do I run a program with a different working directory from current, from Linux shell?

I&#39;ve tried various forms of the following in a bash script:

    #!/bin/bash
    svn diff $@ --diff-cmd /usr/bin/diff -x &quot;-y -w -p -W $COLUMNS&quot;
But I can&#39;t get the syntax to correctly expand the `COLUMNS` environment variable.

I&#39;ve tried various forms of the following:

    svn diff $@ --diff-cmd /usr/bin/diff -x &#39;-y -w -p -W $COLUMNS&#39;
and

    svn diff $@ --diff-cmd /usr/bin/diff -x &#39;-y -w -p -W ${COLUMNS}&#39;
and

    eval svn diff $@ --diff-cmd /usr/bin/diff -x &quot;-y -w -p -W $COLUMNS&quot;

Suggestions?

How to use an environment variable inside a quoted string in Bash

Is it possible to change current directory from a script?

I want to create a utility for directory navigation in Bash. I have created a test script that looks like the following:

    #!/bin/bash
    cd /home/artemb

When I execute the script from the Bash shell the current directory doesn&#39;t change. Is it possible at all to change the current shell directory from a script?

Content Type	Original Author	Original Content on Stackoverflow
Question	Omar Kooheji	View Question on Stackoverflow
Solution 1 - Java	cordellcp3	View Answer on Stackoverflow
Solution 2 - Java	Bill the Lizard	View Answer on Stackoverflow
Solution 3 - Java	phoenix	View Answer on Stackoverflow
Solution 4 - Java	Swapnil1156035	View Answer on Stackoverflow

Java current machine name and logged in user?

Java Problem Overview

Java Solutions

Solution 1 - Java

Solution 2 - Java

Solution 3 - Java

Solution 4 - Java

Can I extend a class using more than 1 class in PHP?

How much overhead does SSL impose?

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