How to declare a constant in Java

Question

We always write    public static final int A   0      Question      Is static final the only way to declare a constant in a class    If I write public final int A   0  instead  is A still a constant or just an instance field    What is an instance variable  What s the difference between an instance variable and an instance field

User · Answer

final means that the value cannot be changed after initialization  that s what makes it a constant  static means that instead of having space allocated for the field in each object  only one instance is created for the class   So  static final means only one instance of the variable no matter how many objects are created and the value of that variable can never change

User · Answer

You can use an enum type in Java 5 and onwards for the purpose you have described  It is type safe  A is an instance variable   If it has the static modifier  then it becomes a static variable   Constants just means the value doesn t change  Instance variables are data members belonging to the object and not the class  Instance variable   Instance field    If you are talking about the difference between instance variable and class variable  instance variable exist per object created  While class variable has only one copy per class loader regardless of the number of objects created   Java 5 and up enum type  public enum Color   RED  Red    GREEN  Green      private Color String color       this color   color         private String color     public String getColor        return this color         public String toString        return this color          If you wish to change the value of the enum you have created  provide a mutator method   public enum Color   RED  Red    GREEN  Green      private Color String color       this color   color         private String color     public String getColor        return this color         public void setColor String color       this color   color         public String toString        return this color          Example of accessing   public static void main String args       System out println Color RED getColor           or    System out println Color GREEN

User · Answer

Anything that is static is in the class level  You don t have to create instance to access static fields method  Static variable will be created once when class is loaded    Instance variables are the variable associated with the object which means that instance variables are created for each object you create  All objects will have separate copy of instance variable for themselves   In your case  when you declared it as static final  that is only one copy of variable  If you change it from multiple instance  the same variable would be updated  however  you have final variable so it cannot be updated    In second case  the final int a is also constant   however it is created every time you create an instance of the class where that variable is declared   Have a look on this Java tutorial for better understanding

[java] How to declare a constant in Java

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