How to store separate constant class for constant variables in Android development

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I have constant variables in Android app like below. I want to move them to a separate constant class so it will be cleaner. What do you suggest? What kind of file do I create in project and do I simply import that constant class in MainActivity class? What I am looking for is similar to constants.h file in C++. What do you guys suggest?

public class MainActivity extends ActionBarActivity {


public static final String NET_SALE = "com.domain.mobile.tipcalculator.MESSAGE1";
public static final String SER_CHRG = "com.domain.mobile.tipcalculator.MESSAGE2";
public static final String TRN_IN = "com.domain.mobile.tipcalculator.MESSAGE3";
public static final String TRN_OUT = "com.domain.mobile.tipcalculator.MESSAGE4";
public static final String POOL = "com.domain.mobile.tipcalculator.MESSAGE5";
public static final String RADIO = "com.domain.mobile.tipcalculator.MESSAGE6";

You can store them in a file with a class that just has public static final variables and use import static com.example.Constants.* to access them.

However, I suggest storing anything that is presented to the user in strings.xml, so that they can be translated.

Best practice for Constant Class in Java, You should strictly avoid using enums on Android. Ideally you should not create class with names like Variables, Parameters, etc. as these names also Besides that, these classes are going to store Constants! Should I create separate constant classes or having them encapsulated in a parent Constant class is fine? The less the constant has the character of a constant but a variable (like version number) the more you can put it outside. The less variable the constant is, so the more constant it is, the more it should placed inside it's scope. During debugging it make sense to place it outside to reduce compilation time.


The common solution is to create a class Constants in which you can put your constants making them public static final. You should also make this class not-instantiable because it just makes sense for it to be instantiated. So you can make its constructor private.

One more solution commonly used is to create an interface that your class can implement. Like this - interface Constants and your class - mainActivity implements Constants. Generally it's considered to be not very good solution, as interfaces are usually used to show class behaviour. You can refer to more info to Effective Java - item 19.

Where should you put constants and why?, I'd say simply that you want to split your huge constants class into many smaller You can still store these files in a central location, but (eg) have 1 file with constants for utils are keyed by an original string - makes things very easy to develop. The less variable the constant is, so the more constant it is, the more it should� Simplest way to implement this is to subclass Android.app.Application class and define static variables that will hold our data. Inside your Android project, create class called for example “AndroidTutorialApp.java” inside your src folder: package com. inchoo. tutorial; import android. app.


My question would be: Where are these constants used? If they're only used within MainActivity, then that's where they should remain. If they're used in multiple locations (which it doesn't look like they are -- are they keys for Intent extras?) then you should look into seeing if it makes sense to have some base class with those values (protected) and just inherit from that class to pass them down.

If you're just using these to provide extras and don't want to have to make them public, you could use a static factory method to create a new Intent to start the Activity, providing the extras internally, and make those constants private:

public static Intent newIntent(Context ctx, String netSale, String serChrg, String trnIn,
                               String trnOut, String pool, String radio) {
    Intent intent = new Intent(ctx, MainActivity.class);
    intent.putExtra(NET_SALE, netSale);
    intent.putExtra(SER_CHRG, serChrg);
    intent.putExtra(TRN_IN, trnIn);
    intent.putExtra(TRN_OUT, trnOut);
    intent.putExtra(POOL, pool);
    intent.putExtra(RADIO, radio);
    return intent;
}

Intelligent constants in your Android App, Have you ever wondered to give those dumb constants some intelligence (or Intellisense)? Enums in Java are feature packed and almost similar to classes public static final int MULTIPLY = 3;private int performOperation(int a, int b, int operation) { } The price of ENUMs from Android Developers� Custom properties (sometimes referred to as CSS variables or cascading variables) are entities defined by CSS authors that contain specific values to be reused throughout a document. They are set using custom property notation (e.g., --main-color: black;) and are accessed using the var() function (e.g., color: var(--main-color);).


Or i would suggest enumerations:

public enum Message{

  NET_SALE("com.domain.mobile.tipcalculator.MESSAGE1"),
  SER_CHRG("com.domain.mobile.tipcalculator.MESSAGE2"),
  TR_IN("com.domain.mobile.tipcalculator.MESSAGE3"),
  TR_OUT("com.domain.mobile.tipcalculator.MESSAGE4"),
  POOL("com.domain.mobile.tipcalculator.MESSAGE5"),
  RADIO("com.domain.mobile.tipcalculator.MESSAGE");
}

Don't put constants everywhere - Michael Spitsin, To be clear I decided to write small post about using constants in For example, you have 3–4 places in application, where timer is needed to be sent. Consider we have class Locale (same to official java class), that have different predefined locales How to Write JUnit5 Parameterised Tests on Android. The way in Android is to associate your variable with the Application context. The way to do this is to create a class and extends with android.app.Application


Java Practices->Class for constants, Concise presentations of java programming practices, tasks, and conventions, Creating a class whose sole job is to define widely-used constants is simple. is an example of <a href='http://www.javapractices.com/Topic2.cjp'>class for� For now, we'll just focus on the constant aspect. Constants are basically variables whose value can't change. In C/C++, the keyword const is used to declare these constant variables. In Java, you use the keyword final. However, the tool introduced here is not simply a primitive variable; it's an actual object instance.


What is a Constant in Java and how to declare it? Edureka, It is one of the fundamental concepts of programming and it does not have a variable 'var' only as static, all the objects of the same class will be able to of the same constant value will be created for every different object and that If we keep the access specifier for a constant variable as private, then its� I create a constant class by looking at some of the best practices described here in stackoverflow. Many of those have a single Constant class with variables. Some of the answers suggested creating separate Contant Classes. The way I create a constant class is by naming it Parameters and creating classes i.e. Variables and Constants.


Learn Java for Android Development: Java 8 and Android 5 Edition, Java 8 and Android 5 Edition Jeff Friesen. Class fields can be modified. If you want a class field to be constant (an unchangeable variable), you must to store these attributes because cars have different makes, models, and door counts. The class no longer requires a <clinit> method, because the constants go into classfile static field initializers, which are handled directly by the VM. Code accessing intVal will use the integer value 42 directly, and accesses to strVal will use a relatively inexpensive "string constant" instruction instead of a field lookup.


const, Constants are block-scoped, much like variables defined using the let keyword. The value of a constant can't be changed through� To keep the user experience (UX) running smoothly, the Android framework provides a helper class called AsyncTask, which processes work off of the UI thread. Using AsyncTask to move intensive processing onto a separate thread means that the UI thread can stay responsive.