Use the `-Werror` flag. It&#39;s not listed in the `-help` output, but it works.

I found it through [this blog entry][1] and tested on my own code (in NetBeans with Ant). The output was:
&lt;pre&gt;
MyClass.java:38: warning: [serial] serializable class MyClass has no definition of serialVersionUID
public class MyClass extends JComponent {
1 warning
BUILD FAILED (total time: 3 seconds)
&lt;/pre&gt;

Note that this is Java 6 only, though.

**Edit**: Example of specifying this in Ant buildfile:

    &lt;javac srcdir=&quot;${src.dir}&quot; destdir=&quot;${classes.dir}&quot; classpathref=&quot;classpath&quot;&gt;
        &lt;compilerarg value=&quot;-Xlint:all&quot;/&gt;
        &lt;compilerarg value=&quot;-Werror&quot;/&gt;
    &lt;/javac&gt;

  [1]: http://weblogs.java.net/blog/tball/archive/2006/11/get_medieval_on.html

Since the vast majority of monitors are [16-bit color or more, including mobile devices](http://en.wikipedia.org/wiki/Web_colors#Web-safe_colors), does it make sense to even consider web-safe colors when choosing color schemes?  Or is it something that ought to be relegated to history as a piece of trivia?

For those of you that don&#39;t know what web-safe colors are:

&gt; Another set of 216 color values is commonly considered to be the &quot;web-safe&quot; color palette, developed at a time when many computer
&gt; displays were only capable of
&gt; displaying 256 colors. A set of colors
&gt; was needed that could be shown without
&gt; dithering on 256-color displays; the
&gt; number 216 was chosen partly because
&gt; computer operating systems customarily
&gt; reserved sixteen to twenty colors for
&gt; their own use; it was also selected
&gt; because it allows exactly six shades
&gt; each of red, green, and blue (6 &#215; 6 &#215;
&gt; 6 = 216).
&gt; 
&gt; The list of colors is often presented
&gt; as if it has special properties that
&gt; render them immune to dithering. In
&gt; fact, on 256-color displays
&gt; applications can set a palette of any
&gt; selection of colors that they choose,
&gt; dithering the rest. These colors were
&gt; chosen specifically because they
&gt; matched the palettes selected by the
&gt; then leading browser applications.  &lt;sup&gt;[[Wikipedia]](http://en.wikipedia.org/wiki/Web_colors#Web-safe_colors)&lt;/sup&gt;


Are web-safe colors still relevant?

I was looking at the `www.google.com` in Firebug and noticed something odd: The Google logo is centered using a center tag.

So I went and checked the page with the [W3C validator][1] and it found 48 errors. Now, I know there are times when you can&#39;t make a page valid, especially when we&#39;re talking about something like `www.google.com` and you want it to be as small as possible, but can someone please explain why they use the center tag? 

[1]: http://validator.w3.org/check?uri=http://www.google.com/&amp;charset=(detect+automatically)&amp;doctype=Inline&amp;group=0

Why does the Google homepage use deprecated HTML (ie. is not valid HTML5)?

I have an Ant file that compiles my program. I want the javac task to fail if any warning was reported by the compiler. Any clue on how to do that?



Make javac treat warnings as errors

<p>I have an Ant file that compiles my program. I want the javac task to fail if any warning was reported by the compiler. Any clue on how to do that?</p>


I&#39;ve a Java object &#39;ChildObj&#39; which is extended from &#39;ParentObj&#39;. Now, if it is possible to retrieve all the attribute names and values of ChildObj, including the inherited attributes too, using Java reflection mechanism?

[Class.getFields][1] gives me the array of public attributes, and [Class.getDeclaredFields][2] gives me the array of all fields, but none of them includes the inherited fields list.

Is there any way to retrieve the inherited attributes also?


  [1]: http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Class.html#getFields()
  [2]: http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Class.html#getDeclaredFields()

Retrieving the inherited attribute names/values using Java Reflection

What is the most elegant way to implement this function:

    ArrayList generatePrimes(int n)

This function generates the first `n` primes (edit: where `n&gt;1`), so `generatePrimes(5)` will return an `ArrayList` with `{2, 3, 5, 7, 11}`. (I&#39;m doing this in C#, but I&#39;m happy with a Java implementation - or any other similar language for that matter (so not Haskell)).

I do know how to write this function, but when I did it last night it didn&#39;t end up as nice as I was hoping. Here is what I came up with:

    ArrayList generatePrimes(int toGenerate)
    {
        ArrayList primes = new ArrayList();
        primes.Add(2);
        primes.Add(3);
        while (primes.Count &lt; toGenerate)
        {
            int nextPrime = (int)(primes[primes.Count - 1]) + 2;
            while (true)
            {
                bool isPrime = true;
                foreach (int n in primes)
                {
                    if (nextPrime % n == 0)
                    {
                        isPrime = false;
                        break;
                    }
                }
                if (isPrime)
                {
                    break;
                }
                else
                {
                    nextPrime += 2;
                }
            }
            primes.Add(nextPrime);
        }
        return primes;
    }

I&#39;m not too concerned about speed, although I don&#39;t want it to be obviously inefficient. I don&#39;t mind which method is used (naive or sieve or anything else), but I do want it to be fairly short and obvious how it works.

**Edit**: Thanks to all who have responded, although many didn&#39;t answer my actual question. To reiterate, I wanted a nice clean piece of code that generated a list of prime numbers. I already know how to do it a bunch of different ways, but I&#39;m prone to writing code that isn&#39;t as clear as it could be. In this thread a few good options have been proposed:

- A nicer version of what I originally had (Peter Smit, jmservera and Rekreativc)
- A very clean implementation of the sieve of Eratosthenes (starblue)
- Use Java&#39;s `BigInteger`s and `nextProbablePrime` for very simple code, although I can&#39;t imagine it being particularly efficient (dfa)
- Use LINQ to lazily generate the list of primes (Maghis)
- Put lots of primes in a text file and read them in when necessary (darin)

**Edit 2**: I&#39;ve [implemented in C#][1] a couple of the methods given here, and another method not mentioned here. They all find the first *n* primes effectively (and I have a [decent method][2] of finding the limit to provide to the sieves).


  [1]: https://stackoverflow.com/questions/1042902/most-elegant-way-to-generate-prime-numbers/1072205#1072205
  [2]: https://stackoverflow.com/questions/1042717/is-there-a-way-to-find-the-approximate-value-of-the-nth-prime/1069023#1069023

Most elegant way to generate prime numbers

It&#39;s right there, in the package that it should be indexing. Still, when I call

    JAXBContext jc = JAXBContext.newInstance(&quot;my.package.name&quot;);

I get a JAXBException saying that 

&gt; &quot;my.package.name&quot; doesnt contain ObjectFactory.class or jaxb.index

although it does contain both.

What does work, but isn&#39;t quite what I want, is

    JAXBContext jc = JAXBContext.newInstance(my.package.name.SomeClass.class);

This question from various other people appears on quite some mailing lists and forums but seemingly doesn&#39;t get answers.

I&#39;m running this on OpenJDK 6, so I got the source packages and stepped my debugger into the library. It starts by looking for jaxb.properties, then looks for system properties and failing to find either, it tries to create the default context using com.sun.internal.xml.bind.v2.ContextFactory. In there, the Exception gets thrown (inside `ContextFactor.createContext(String ClassLoader, Map)`), but I can&#39;t see what&#39;s going on because the source isn&#39;t here.

**ETA**:

Judging from the source code for ContentFactory, I found [here][1], this is probably the piece of code that fails to work as intended:

    /**
     * Look for jaxb.index file in the specified package and load it&#39;s contents
     *
     * @param pkg package name to search in
     * @param classLoader ClassLoader to search in
     * @return a List of Class objects to load, null if there weren&#39;t any
     * @throws IOException if there is an error reading the index file
     * @throws JAXBException if there are any errors in the index file
     */
    private static List&lt;Class&gt; loadIndexedClasses(String pkg, ClassLoader classLoader) throws IOException, JAXBException {
        final String resource = pkg.replace(&#39;.&#39;, &#39;/&#39;) + &quot;/jaxb.index&quot;;
        final InputStream resourceAsStream = classLoader.getResourceAsStream(resource);

        if (resourceAsStream == null) {
            return null;
        }

From my [previous][2] [experience][3], I&#39;m guessing that this has to do with the class loading mechanisms of the OSGi container that this is running in. Unfortunately, I am still a little out of my depth here.

[1]: http://www.java2s.com/Open-Source/Java-Document/6.0-JDK-Modules-com.sun/xml/com/sun/xml/internal/bind/v2/ContextFactory.java.htm#createContextStringClassLoaderMapStringObject
[2]: https://stackoverflow.com/questions/1034132/can-i-put-annotations-for-multiple-processors-into-a-java-class
[3]: https://stackoverflow.com/questions/1037356/how-do-i-debug-silent-failures-in-java-applications

Why can&#39;t JAXB find my jaxb.index when running inside Apache Felix?

I have a Java project in Eclipse with ~10 packages and ~10 class files per package.  Is there a way to determine total lines of code for the whole project from within Eclipse?  I am familiar with other tools (e.g., Code Analyzer, wc, etc.) but I want to know if there is a way to do this within Eclipse (or get confirmation that there is no way to do it).

Counting Line Numbers in Eclipse

Given these two commands

A:

    $ java -Xms10G -Xmx10G myjavacode input.txt

B:

    $ java -Xms5G -Xmx5G myjavacode input.txt

I have two questions:

 1. Since command A reserves more memory with its parameters, will A run faster than B? 
 2. How do `-Xmx` and `-Xms` affect the running process and the output of my program?

Speed tradeoff of Java&#39;s -Xms and -Xmx options

What does another build tool targeted at Java really get me?

If you use Gradle over another tool, why?


Why use Gradle instead of Ant or Maven?

How do I check for the existence of a folder using Ant?

We can check the existence of a file, but can we do the same for a folder as well?


Do I have a way to check the existence of a directory in Ant (not a file)?

Is there a simple way of taking the value of a property and then copy it to another property with certain characters replaced?

Say `propA=This is a value`. I want to replace all the spaces in it into underscores, resulting in `propB=This_is_a_value`.

Replacing characters in Ant property

I am upgrading a large build-system to use Maven2 instead of Ant, and we have two related requirements that I&#39;m stuck on:

 1. We need to generate a time-stamped artifact, so a part of the *package*
    phase (or wherever), instead of building 

        project-1.0-SNAPSHOT.jar

    we
    should be building 

        project-1.0-20090803125803.jar

    (where the
    `20090803125803` is just a `YYYYMMDDHHMMSS` time-stamp of when the jar is
    built).

    The only real requirement is that the time-stamp be a part of the
    generated file&#39;s filename.

 2. The same time-stamp has to be included within a *version.properties* file
    inside the generated jar.

This information is included in the generated *pom.properties* when you run,
e.g., `mvn package` but is commented out:

    #Generated by Maven
    #Mon Aug 03 12:57:17 PDT 2009

Any ideas on where to start would be helpful!  Thanks!

How do I add time-stamp information to Maven artifacts?

I am writing a bash script to automate the build process. There are two major build blocks, one is an ant task and one is a plain old `mvn clean install`. I want to do something when there is build error coming from either of this two build processes. 

The problem is, these builds will contain test failures or errors from time to time, but the end result is successful. And I believe that the status code ($?) return by these processes should be 0 no matter the build fail or succeed, I could be wrong.

So what is the best way for my script to detect the end result (build fail/succeed) without catching the false info during the mid build (test errors, etc) from them?

how to detect a build error from ant/maven via a bash script?

I have a `select()` method in a database class, that has an optional boolean argument `$sum`. This argument is used to say if the method should use `COUNT(*)` or not too.

I would like to show a warning, like those normal PHP errors, if I try to access `$class-&gt;sum` if the attribute is not set (i.e. when I call `select()` with `$sum == false`.

Is there any way to show a warning like this, or I should just echo an error and be happy?

Is there any way to show, or throw, a PHP warning?

I need to parse some HTML files, however, they are not well-formed and PHP prints out warnings to. I want to avoid such debugging/warning behavior programatically. Please advise. Thank you!

Code:

    // create a DOM document and load the HTML data
    $xmlDoc = new DomDocument;
    // this dumps out the warnings
    $xmlDoc-&gt;loadHTML($fetchResult);

This:

    @$xmlDoc-&gt;loadHTML($fetchResult)

can  suppress the warnings but how can I capture those warnings programatically?

Disable warnings when loading non-well-formed HTML by DomDocument (PHP)

What is the list of valid `@SuppressWarnings` warning names in Java?

The bit that comes in between the `(&quot;&quot;)` in `@SuppressWarnings(&quot;&quot;)`.

What is the list of valid @SuppressWarnings warning names in Java?

If I use `malloc` in my code:

    int *x = malloc(sizeof(int));

I get this warning from `gcc`:

    new.c:7: warning: implicit declaration of function ‘malloc’  
    new.c:7: warning: incompatible implicit declaration of built-in function ‘malloc’


Why do I get a warning every time I use malloc?

I have the following class (from a simple Spring tutorial)

    public class CarValidator implements Validator {
    
        public boolean supports(Class aClass) {
            return Car.class.equals(aClass);
        }
    
        public void validate(Object obj, Errors errors) {
            Car car = (Car) obj;
    
            ValidationUtils.rejectIfEmptyOrWhitespace(errors, &quot;model&quot;, &quot;field.required&quot;, &quot;Required field&quot;);
    
            ValidationUtils.rejectIfEmptyOrWhitespace(errors, &quot;price&quot;, &quot;field.required&quot;, &quot;Required field&quot;);
    
            if( ! errors.hasFieldErrors(&quot;price&quot;)) {
                if (car.getPrice().intValue() == 0) {
                    errors.rejectValue(&quot;price&quot;, &quot;not_zero&quot;, &quot;Can&#39;t be free!&quot;);
                }
            }
    
        }
    }
    
Where the Validator class is the `org.springframework.validation.Validator` class from Spring 2.5.

The supports method is showing a warning (Class is a raw type. References to generic type Class&lt;T&gt; should be parameterized), if I try to add parameters to this such as 

    public boolean supports(Class&lt;?&gt; aClass) ...

I get the following error:

```The method supports(Class&lt;?&gt;) of type CarValidator has the same erasure as supports(Class) of type Validator but does not override it```

There are lots of threads about this type of question, but I want to get a complete answer and actually understand it without &#39;hiding&#39; the problem with a `@SupressWarnings`!

Class is a raw type. References to generic type Class&lt;T&gt; should be parameterized

&lt;pre&gt;C:\Program Files\Java\jdk1.6.0_05\CoreJava\v1\v1ch2\WelcomeApplet&gt;dir
 Volume in drive C has no label.
 Volume Serial Number is 2041-64E7

 Directory of C:\Program Files\Java\jdk1.6.0_05\CoreJava\v1\v1ch2\WelcomeApplet

2009-07-02  23:54    &lt;DIR&gt;          .
2009-07-02  23:54    &lt;DIR&gt;          ..
2004-09-06  14:57               582 WelcomeApplet.html
2004-09-06  15:04             1,402 WelcomeApplet.java
               2 File(s)          1,984 bytes
               2 Dir(s)   2,557,210,624 bytes free

C:\Program Files\Java\jdk1.6.0_05\CoreJava\v1\v1ch2\WelcomeApplet&gt;javac WelcomeApplet.java

C:\Program Files\Java\jdk1.6.0_05\CoreJava\v1\v1ch2\WelcomeApplet&gt;dir
 Volume in drive C has no label.
 Volume Serial Number is 2041-64E7

 Directory of C:\Program Files\Java\jdk1.6.0_05\CoreJava\v1\v1ch2\WelcomeApplet

2009-07-02  23:54    &lt;DIR&gt;          .
2009-07-02  23:54    &lt;DIR&gt;          ..
2009-07-02  23:54               975 WelcomeApplet$1.class
2009-07-02  23:54             1,379 WelcomeApplet.class
2004-09-06  14:57               582 WelcomeApplet.html
2004-09-06  15:04             1,402 WelcomeApplet.java
               4 File(s)          4,338 bytes
               2 Dir(s)   2,557,202,432 bytes free

C:\Program Files\Java\jdk1.6.0_05\CoreJava\v1\v1ch2\WelcomeApplet&gt;
&lt;/pre&gt;


Here is the content of that Java file:

    /**
       @version 1.21 2002-06-19
       @author Cay Horstmann
    */
    
    import javax.swing.*;
    import java.awt.*;
    import java.awt.event.*;
    import java.net.*;
    
    public class WelcomeApplet extends JApplet
    {
       public void init()
       {
          setLayout(new BorderLayout());
    
          JLabel label = new JLabel(getParameter(&quot;greeting&quot;), SwingConstants.CENTER);
          label.setFont(new Font(&quot;Serif&quot;, Font.BOLD, 18));
          add(label, BorderLayout.CENTER);
    
          JPanel panel = new JPanel();
    
          JButton cayButton = new JButton(&quot;Cay Horstmann&quot;);
          cayButton.addActionListener(makeURLActionListener(
             &quot;http://www.horstmann.com&quot;));
          panel.add(cayButton);
    
          JButton garyButton = new JButton(&quot;Gary Cornell&quot;);
          garyButton.addActionListener(makeURLActionListener(
             &quot;mailto:gary@thecornells.com&quot;));
          panel.add(garyButton);
    
          add(panel, BorderLayout.SOUTH);
       }
    
       private ActionListener makeURLActionListener(final String u)
       {
          return new
             ActionListener()
             {
                public void actionPerformed(ActionEvent event)
                {
                   try
                   {
                      getAppletContext().showDocument(new URL(u));
                   }
                   catch(MalformedURLException e) 
                   { 
                      e.printStackTrace(); 
                   }
                }
             };
       }
    }



What is the $1 in class file names?

In which languages are the Java *compiler* (`javac`), the virtual machine (JVM) and the `java` starter written?


In which language are the Java compiler and JVM written?

I need to compile a jar file using ant (1.7.0) to run under a specific version of Java (1.5). I currently have Java 1.6 on my machine. I have tried setting:

    &lt;target name=&quot;compile&quot;&gt;
      &lt;javac compiler=&quot;javac1.5&quot; target=&quot;1.5&quot; srcdir=.../&gt;
    &lt;/target&gt;

I have also removed 

    &lt;property name=&quot;build.compiler&quot; value=&quot;modern&quot;/&gt;

and there is no properties file. I am running Java 1.6 on Linux/SUSE

Also is there a simple way of determining which version of Java is expected in the jar file.


Setting the target version of Java in ant javac

When I compile, javac outputs:

    Note: Some input files use or override a deprecated API.
    Note: Recompile with -Xlint:deprecation for details.`

I wish to suppress this warning. Trying -Xlint:none does not seem to help.

How can I suppress javac warnings about deprecated api?

I&#39;m trying to use `javac` with the windows command prompt, but it&#39;s not working.

After adding the directory `&quot;C:\Program Files\Java\jdk1.6.0_16\bin\&quot;` to the end of the `PATH` environment variable, the `java` command works fine, but using `javac` gives me the following error:

&gt; &#39;javac&#39; is not recognized as an internal or external command, operable program or batch file.

Content Type	Original Author	Original Content on Stackoverflow
Question	Itay Maman	View Question on Stackoverflow
Solution 1 - Java	Michael Myers	View Answer on Stackoverflow

Make javac treat warnings as errors

Java Problem Overview

Java Solutions

Solution 1 - Java

Why does the Google homepage use deprecated HTML (ie. is not valid HTML5)?

Are web-safe colors still relevant?

Attributions