Java Color class question

[toString]

Here's the method I'm trying to use:
http://java.sun.com/j2se/1.5.0/docs/api/java/awt/Color.html#getColor(java.lang.String)

And I would have suspected at least one of these would have returned something, but they all return null!

System.out.println(Color.getColor("Color.RED"));
System.out.println(Color.getColor("Color.red"));
System.out.println(Color.getColor("red"));
System.out.println(Color.getColor("RED"));

How am I using this incorrectly?! It is a bit late, but I really don't understand it

 

[Welshy]

Have you imported java.awt.Color? Other than that, I can't think of anything off the top of my head.

 

[toString]

Yeah it's imported fine. I get no errors. It's just doing what the method should do if it can't find the color, i.e. return null. But I don't know what sort of string I'm supposed to input to get a proper return value.

I even made a small test class just to check it wasn't anything else causing problems:

import java.awt.Color;

public class Test {
  public static void main(String[] args) {
    System.out.println(Color.getColor("Color.RED"));
    System.out.println(Color.getColor("Color.red"));
    System.out.println(Color.getColor("red"));
    System.out.println(Color.getColor("RED"));
    System.out.println(Color.getColor("java.awt.Color.RED"));
  }
}

There must be something obvious but I can't even see anything on google!

 

[triggerthat]

It returns a static color, which should be used in an Applet.

 

[toString]

That's the point, it doesn't return anything!

If it returned a color we'd see the toString of the color and not NULL.

 

[Visage]

From the API documentation:

getColor

public static Color getColor(String nm)

    Finds a color in the system properties.

    The argument is treated as the name of a system property to be obtained. The string value of this property is then interpreted as an integer which is then converted to a Color object.

    If the specified property is not found or could not be parsed as an integer then null is returned.

    Parameters:
        nm - the name of the color property 
    Returns:
        the Color converted from the system property.
    Since:
        JDK1.0
    See Also:
        System.getProperty(java.lang.String), Integer.getInteger(java.lang.String), Color(int)

So if you use a line like:

System.out.println(Color.getColor("Color.RED"));

Then it will only output something if you have a system property names "Color.RED". The fact that its quoted is the giveaway - its a string literal - only through reflection can it be related to the Color class.

The idea is that in your system properties you have a line like:

indigo=12345.

Then when you do Color.getColor("indigo") you get a colour thats been created from the string "12345", pasred as an int, and then used in the Color constructor that takes an int.

In short, Color.getColor("someString") is semantically identical to:

String text = System.GetProperty("someString") ;
Color c = new Color(text.asInt()) ;

 

[toString]

Thanks for that Visage!
It seems that I got the wrong interpretation of what this method does.

What I need is something like this:

String inputCommand = commandJTextField.getText();

if (Color.getColor(inputCommand) != null) {
	System.out.println("a valid color");
} else {
	System.out.println("an invalid color");
}

Where the user enters say... 'red' and I want to work out if it's a attribute of the Color class.
But I'm not sure that it's possible now. Any help would be great.

The only other way I can think is to have a massive if/else if structure where I define all the colors that the Color class supports.
But that's hardly ideal.

 

[Una]

Edit: Ah I see now.

 

[Dj_Jestar]

just create an array of known colours, then cross-ref. Avoids the need to import Color.

 

[Visage]

Thanks for that Visage!
It seems that I got the wrong interpretation of what this method does.

What I need is something like this:

String inputCommand = commandJTextField.getText();

if (Color.getColor(inputCommand) != null) {
	System.out.println("a valid color");
} else {
	System.out.println("an invalid color");
}

Where the user enters say... 'red' and I want to work out if it's a attribute of the Color class.
But I'm not sure that it's possible now. Any help would be great.

The only other way I can think is to have a massive if/else if structure where I define all the colors that the Color class supports.
But that's hardly ideal.

Doesnt that run into the problem of defining what is and isnt a colour?

Is red a colour? Yes What about olive? Probably....

EDIT: Actually,m if you wanted to use one of the standard Color statc members then you could use reflection to do it.....

 

[toString]

It's supposed to be just for the colours in the Color class, so things like purple or brown don't matter if they're entered.
I could use an array, but spec-ing out 15ish colours that are repeated elsewhere doesn't really 'feel' right. Even if if it's the simple way!

However, thanks for the reflection idea! I've finally got something that does exactly what I need. Here it is, for those who might be interested in a happy ending:

private Color getInputColor(String colorString) {
	try {
		Field field = Class.forName("java.awt.Color").getField(colorString);
		return (Color) field.get(field);
	} catch (Exception e) {
		return null;
	}
}

 

[Dj_Jestar]

class ColourChecker
{
    private String[] colours;

    public ColourChecker ()
    {
        this.colours = {
            "red",
            "blue",
            "yellow",
            "orange",
            "green",
            "purple",
            "pink"
        };
    }
    
    public boolean isColour (String colour)
    {
        if (this.colours.indexOf(String.toLower(colour)) !== false) return true;

        return false;
    }
}