How can I have a constant variable common to all classes in a package?

I want a constant variable to be common to all classes in a package. Is there a way I can do this without making an interface just with the one definition in it, a开发者_开发技巧nd making every class implement that?

In Java, all constants have to reside in a type (class or interface). But you don't have to implement an interface to use a constant declared inside.

You can try by putting something like this in your package:

interface Constants {

    static final String CONSTANT = "CONTANT";

}

and then, using it like this:

String myVar = Constants.CONSTANT;

This way, you still have your interface, but no classes implement it.

Generally applications have a "Constants" class or interface that holds all constants.

I generally to to group constants into logical classes. For instance if there can be two kinds of employees, regular and contract:

class EmployeeType
{
   public static final String REGULAR = "regular";
   public static final String CONTRACT = "contract";
}

and use it as EmployeeType.REGULAR

If the constants cannot be grouped this way, have a separate class/interface to hold these.

class Constants
{
   public static final String APPLICATION_DOMAIN = 'domain';
}

You need not extend/implement this class interface to use the values. The constants will generally be declared public static final, you can access them directly: Constants.APPLICATION_DOMAIN

Use a package private class:

class Constants{

    public static final int MY_VALUE = 1234;

}

This can only be accessed by classes from the same package:

int val = Constants.MY_VALUE;

You can do this in various ways:

• One way (as mentioned here) is to create a Global constant interface and have a public static final attributes of each constants.`
• Create properties file. By having a properties file, you'll have a Key value pair (separated by a = operator) each declared on a newline. Here's a tutorial on how to create and use properties file.

Seems like to be a good candidate for an entry in a property file to me.

You can use an abstract class to serve as the base class for each impls in that package.

You could make a special (static) class with just this variable. Later you can add other constants or whatever you need to that class.