There&#39;s the code itself:

    public final static Color red = new Color(255, 0, 0);
    
    public final static Color RED = red;

The upper case letters were introduced in JDK 1.4 (to conform to its naming convention, stating that constants **must** be in upper-case). 

In essence, there are no difference at all (except letter casing).

-------------

If I want to really be brave, Oracle might go wild and remove constants that is lower-cased, but then that would break all other code that&#39;s written pre-JDK 1.4. You never know, I would suggest sticking to uppercase letters for constants. It first has to be deprecated though (as mentioned by Andrew Thompson).

There is really no difference. See the `Color` class:

    /**
     * The color red.  In the default sRGB space.
     */
    public final static Color red       = new Color(255, 0, 0);

    /**
     * The color red.  In the default sRGB space.
     * @since 1.4
     */
    public final static Color RED = red;

Java defined some color constant names in lowercase, which violated the naming rule of using uppercase for constants.
Heres the code for the color red:

    public final static Color red = new Color(255, 0, 0); 

Later on they made the same colors but in uppercase.

    public final static Color RED = red;

So there is really no difference. They are all the same, as you can tell by the code.

    public final static Color red = new Color(255, 0, 0);
    public final static Color RED = red;

Hope this helps!



I&#39;m writing a web service that returns a base64-encoded PDF file, so my plan is to add two headers to the response:

    Content-Type: application/pdf
    Content-Transfer-Encoding: base64

My question is: Is `Content-Transfer-Encoding` a valid HTTP header?  I think it might only be for MIME.  If not, how should I craft my HTTP response to represent the fact that I&#39;m returning a base64-encoded PDF?  Thanks.

**EDIT:** 

It looks like HTTP does not support this header.  From [RFC2616 Section 14][1]:

&gt; Note: while the definition of Content-MD5 is exactly the same for HTTP
&gt; as in RFC 1864 for MIME entity-bodies, there are several ways in which
&gt; the application of Content-MD5 to HTTP entity-bodies differs from its
&gt; application to MIME entity-bodies. One is that **HTTP, unlike MIME, does
&gt; not use Content-Transfer-Encoding**, and does use Transfer-Encoding and
&gt; Content-Encoding.

Any ideas for what I should set my headers to?  Thanks.

**EDIT 2**

Many of the code samples found in the comments of this PHP reference manual page seem to suggest that it actually *is* a valid HTTP header:

http://php.net/manual/en/function.header.php

  [1]: http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html

Is Content-Transfer-Encoding an HTTP header?

So I understand (I think) about broadcast intents and receiving messages to them.

So now, my problem/what I can&#39;t work out is how to send a message from the `onReceive` method of a receiver to an activity. Lets say I have a receiver as such:

    public class ReceiveMessages extends BroadcastReceiver 
    {
    @Override
       public void onReceive(Context context, Intent intent) 
       {    
           String action = intent.getAction();
           if(action.equalsIgnoreCase(TheService.DOWNLOADED)){    
               // send message to activity
           }
       }
    }

How would I send a message to an activity?

Would I have to instantiate the receiver in the activity I want to send messages to and monitor it somehow? Or what? I understand the concept, but not really the application.

Any help would be absolutely amazing, thank you.

Tom

Using a broadcast intent/broadcast receiver to send messages from a service to an activity

What&#39;s the real difference between definitions for `setXxx(Color.red)` and `setXxx(Color.RED)`?

I&#39;ve found the following explanation on the web. Is it all about naming conventions?

&gt; Java originally defined a few color constant names in lowercase, which violated  the naming rule of using uppercase for constants. They are available in all versions of Java: Color.black, Color.darkGray, Color.gray, Color.lightGray, Color.white, Color.magenta, Color.red, Color.pink, Color.orange, Color.yellow, Color.green, Color.cyan, Color.blue
&gt;
&gt; Java 1.4 added the proper uppercase names for constants: Color.BLACK, Color.DARK_GRAY, Color.GRAY, Color.LIGHT_GRAY, Color.WHITE, Color.MAGENTA, Color.RED, Color.PINK, Color.ORANGE, Color.YELLOW, Color.GREEN, Color.CYAN, Color.BLUE

Difference between Color.red and Color.RED

What's the real difference between definitions for <code>setXxx(Color.red)</code> and <code>setXxx(Color.RED)</code>?
I've found the following explanation on the web. Is it all about naming conventions?
> Java originally defined a few color constant names in lowercase, which violated the naming rule of using uppercase for constants. They are available in all versions of Java: Color.black, Color.darkGray, Color.gray, Color.lightGray, Color.white, Color.magenta, Color.red, Color.pink, Color.orange, Color.yellow, Color.green, Color.cyan, Color.blue
>
> Java 1.4 added the proper uppercase names for constants: Color.BLACK, Color.DARK_GRAY, Color.GRAY, Color.LIGHT_GRAY, Color.WHITE, Color.MAGENTA, Color.RED, Color.PINK, Color.ORANGE, Color.YELLOW, Color.GREEN, Color.CYAN, Color.BLUE

I just noticed that java.util.Observable is a concrete class. Since the purpose of Observable is to be extended, this seems rather odd to me. Is there a reason why it was implemented this way?

I found [this article][1] which says that 

&gt; The observable is a concrete class, so the class deriving from it must be determined upfront, as Java allows only single inheritance.

But that doesn&#39;t really explain it to me. In fact, if Observable were abstract, the user would be forced to determine the class deriving from it. 


  [1]: http://javanook.tripod.com/patterns/observer.html

Why is java.util.Observable not an abstract class?

Why doesn&#39;t `Set` provide an operation to get an element that equals another element?

    Set&lt;Foo&gt; set = ...;
    ...
    Foo foo = new Foo(1, 2, 3);
    Foo bar = set.get(foo);   // get the Foo element from the Set that equals foo

I can ask whether the `Set` contains an element equal to `bar`, so why can&#39;t I get that element? :(

To clarify, the `equals` method is overridden, but it only checks one of the fields, not all. So two `Foo` objects that are considered equal can actually have different values, that&#39;s why I can&#39;t just use `foo`.

Getting an element from a Set

When I call `Math.ceil(5.2)` the return is the `double` `6.0`. My natural inclination was to think that `Math.ceil(double a)` would return a `long`. From the documentation:

&gt; `ceil(double a)`
&gt; 
&gt; Returns the smallest (closest to negative infinity) `double` value
&gt; that is not less than the argument and is equal to a mathematical
&gt; integer.

But why return a `double` rather than a `long` when the result is an integer? I think understanding the reason behind it might help me understand Java a bit better. It also might help me figure out if I&#39;ll get myself into trouble by casting to a `long`, e.g. is

`long b = (long)Math.ceil(a);`

always what I think it should be? I fear there could be some boundary cases that are problematic.


Why does Math.ceil return a double?

I have two packages, `Shapes` and `Fruits`:

    com.myproject.Shapes.
        Circle
        Square
        Triangle
    com.myproject.Fruits.
        Apple
        Orange

I am writing the JavaDoc for `Apple` and need to provide an `{@link}` to `Square`.

I have tried all of the following, and none of them work:

    {@link Square}
    {@link com.myproject.Square}

I&#39;ve been able to find documentation for linking to: (a) classes within the same package, or (b) externals URLs, but not classes in another package.

Any ideas what the correct syntax should be? Thanks!

Javadoc linking to a class in another package

I have an object that contains a few unserializable fields that I want to serialize. They are from a separate API that I cannot change, so making them Serializable is not an option. The main problem is the Location class. It contains four things that can be serialized that I&#39;d need, all ints. How can I use read/writeObject to create a custom serialization method that can do something like this:

    // writeObject:
    List&lt;Integer&gt; loc = new ArrayList&lt;Integer&gt;();
    loc.add(location.x);
    loc.add(location.y);
    loc.add(location.z);
    loc.add(location.uid);
    // ... serialization code

    // readObject:
    List&lt;Integer&gt; loc = deserialize(); // Replace with real deserialization
    location = new Location(loc.get(0), loc.get(1), loc.get(2), loc.get(3));
    // ... more code

How can I do this?

Java Custom Serialization

For example:

`AA33FF` = valid hex color

`Z34FF9` = invalid hex color (has Z in it)

`AA33FF11` = invalid hex color (has extra characters)



How to check if a string is a valid hex color representation?

I&#39;ve had this a few times, so here goes: I&#39;m making some plots which hold curves with estimates of a parameter given a tuning parameter.

Typically, I also have SDs for each estimated value, so I could show error bars around each of them.

However, I don&#39;t like error bars, and would prefer some smoothed version of it. This is in itself no problem (ie I know how to do this). However, my plot contains several of these similar curves, each one in its own color. So I would like to add the &#39;smoothed errorregion&#39; to each curve in a color that matches the color of the curve itself. Of course, I would like to do this somewhat transparently, so I can still see the other curves through the &#39;error region&#39;.

So, my question is: given a color (specified by either a number, a name or an rgb value --- note the first two pose an extra problem, but this is occurring rather often, as the basic plotting functions take these as valid color values), how can I find find the matching color that has the same rgb but a different (given) alpha level (transparency). I would like a function like:

    makeTransparent&lt;-function(someColor, alpha=100)
    {
      newColor&lt;-someColor + alpha #I wish
      return(newColor)
    }

This should work for things like:

    makeTransparent(2)
    makeTransparent(&quot;red&quot;)
    makeTransparent(rgb(0,0,1))

**Edit** I hate it when I miss something obvious, but @themel pointed me to it (thx again). Here&#39;s a full solution (note: works vectorized, so you can pass more than one color; only one alpha is supported at this time though):

    #note: always pass alpha on the 0-255 scale
    makeTransparent&lt;-function(someColor, alpha=100)
    {
      newColor&lt;-col2rgb(someColor)
      apply(newColor, 2, function(curcoldata){rgb(red=curcoldata[1], green=curcoldata[2],
        blue=curcoldata[3],alpha=alpha, maxColorValue=255)})
    }



Transparent equivalent of given color

You can understand why I&#39;m trying to find the dominant color in an image if you use Windows 7.  When your mouse over a program in the taskbar, the background of that particular program changes based on the most dominant color in the icon.  I have noticed this technique used in other programs as well, but can&#39;t remember them off the top of my head.

I can see this being helpful in a number of UI techniques that I&#39;m using to develop an application, and I was wondering how finding the most common color would be achieved from an Android drawable resource.

Finding the dominant color of an image in an Android @drawable

When I have a diff, how can I colorize it so that it looks good?

I want it for the command line, so please no GUI solutions.


How to colorize diff on the command line

I want to design a program that can help me assess between 5 pre-defined colors which one is more similar to a variable color, and with what percentage.  The thing is that I don&#39;t know how to do that manually step by step. So it is even more difficult to think of a program.

More details: The colors are from photographs of tubes with gel that as different colors. I have 5 tubes with different colors were each is representative of 1 of 5 levels. I want to take photographs of other samples and on the computer assess to which level that sample belongs by comparing colors, and I want to know that with a percentage of approximation too. I would like a program that does something like this: http://www.colortools.net/color_matcher.html

If you can tell me what steps to take, even if they are things for me to think and do manually. It would be very helpful. 

Content Type	Original Author	Original Content on Stackoverflow
Question	mKorbel	View Question on Stackoverflow
Solution 1 - Java	Buhake Sindi	View Answer on Stackoverflow
Solution 2 - Java	Jan Zyka	View Answer on Stackoverflow
Solution 3 - Java	Artem Katerynych	View Answer on Stackoverflow

Difference between Color.red and Color.RED

Java Problem Overview

Java Solutions

Solution 1 - Java

Solution 2 - Java

Solution 3 - Java

Using a broadcast intent/broadcast receiver to send messages from a service to an activity

Is Content-Transfer-Encoding an HTTP header?

Attributions