What is the best way to implement constants in Java? [closed]

Answer 1

For Constants, Enum is a better choice IMHO. Here is an example

public class myClass {

public enum myEnum {
    Option1("String1", 2), 
    Option2("String2", 2) 
    ;
    String str;
            int i;

            myEnum(String str1, int i1) { this.str = str1 ; this.i1 = i }


}

Answer 2

One of the way I do it is by creating a 'Global' class with the constant values and do a static import in the classes that need access to the constant.

Answer 3

In Effective Java (2nd edition), it's recommended that you use enums instead of static ints for constants.

There's a good writeup on enums in Java here: http://java.sun.com/j2se/1.5.0/docs/guide/language/enums.html

Note that at the end of that article the question posed is:

So when should you use enums?

With an answer of:

Any time you need a fixed set of constants

Answer 4

What about an enumeration?

Answer 5

A single, generic constants class is a bad idea. Constants should be grouped together with the class they're most logically related to.

Rather than using variables of any kind (especially enums), I would suggest that you use methods. Create a method with the same name as the variable and have it return the value you assigned to the variable. Now delete the variable and replace all references to it with calls to the method you just created. If you feel that the constant is generic enough that you shouldn't have to create an instance of the class just to use it, then make the constant method a class method.

Answer 6

It is a BAD PRACTICE to use interfaces just to hold constants (named constant interface pattern by Josh Bloch). Here's what Josh advises:

If the constants are strongly tied to an existing class or interface, you should add them to the class or interface. For example, all of the boxed numerical primitive classes, such as Integer and Double, export MIN_VALUE and MAX_VALUE constants. If the constants are best viewed as members of an enumerated type, you should export them with an enum type. Otherwise, you should export the constants with a noninstantiable utility class.

Example:

// Constant utility class
package com.effectivejava.science;
public class PhysicalConstants {
    private PhysicalConstants() { }  // Prevents instantiation

    public static final double AVOGADROS_NUMBER   = 6.02214199e23;
    public static final double BOLTZMANN_CONSTANT = 1.3806503e-23;
    public static final double ELECTRON_MASS      = 9.10938188e-31;
}

About the naming convention:

By convention, such fields have names consisting of capital letters, with words separated by underscores. It is critical that these fields contain either primitive values or references to immutable objects.