Objective of instance variable in interface

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In interface instance variable is by default static and final. if instance variable in interface is final then we must initialize so what is objective to define instance variable in interface or what is use of instance variable in interface???

Variables in interface are static final. They are available to all the classes which are implementing it. So to set some parameters which will be used throughout the application can be set here. Rough eg you can set the name of the application which can be used by all the classes.

Java Interfaces, Notice how the variable is declared to be of the interface type MyInterface while the object created is of type MyInterfaceImpl . The preference is generally to place private instance variables and properties in the private class extension (in the.m) and leave the public interface file (.h) for those properties and methods that are truly part of the public interface. It helps isolate implementation details from the public interface and makes everything much cleaner.

First of All, Interfaces cannot have instance variables.

An "instance variable" means an "instance field."

An instance field is a field that is specific to an individual instance of a class. For example:

class Foo {
    // Instance field:
    private int bar;

    // Static field:
    public static final int staticBar;
}  

The field bar is per-instance, and is not class-wide. The field staticBar is class-wide (a static field, sometimes called a "class field").

Interfaces don't have instance fields. They do have static fields. When you do this:

interface FooInterface {
    int staticBar;
}  

staticBar is automatically declared public, static, and final. So that staticBar is roughly equivalent to the one on our Foo class before.

For more help, refer this question

Using an Interface as a Type (The Java™ Tutorials > Learning the , If you define a reference variable whose type is an interface, any object you assign to it must be an instance of a class that implements the interface. This gives them some of the advantages of multiple inheritance, where they can have behavior from both a superclass and an interface. The ClassMemberssection of the interface defines the variables that are to be contained within the class (also referred to as instance variables). The ClassMethodssection defines the methods that are available to be called on the class. These are essentially functions specific to the class that perform a particular operation when called upon.

Interface interf{
 int i = 10;
}

1) Interface has by default has access modifier. So no object is created for interface for accessing any attributes or component.

2) Any variable define in interface are by default public, static, final - CONSTANT. As a variable is declared as static is can be access without object.

NOTE : No , interface does not contain instance variable.

Interface variables are static and final by default in Java, Why?, Interface variables are static and final by default in Java, Why? JavaObject Oriented ProgrammingProgramming. An interface defines a protocol of� A static variable accessible to all class instances to store the instance count A declaration for a our newAlloc class method in the @interface section A declaration for a class method to return the current value of the instance count in the @interface section

Instance Variable In Java, Features of an instance variable � Instance Variable can be used only by creating objects � Every object will have its own copy of Instance variables� If you define a reference variable whose type is an interface, any object you assign to it must be an instance of a class that implements the interface. As an example, here is a method for finding the largest object in a pair of objects, for any objects that are instantiated from a class that implements Relatable: public Object findLargest (Object object1, Object object2) { Relatable obj1 = (Relatable)object1; Relatable obj2 = (Relatable)object2; if ( (obj1).isLargerThan (obj2) > 0) return

Java Interfaces, All variables declared inside interface are implicitly public, static and final. Interface is a Java Object containing method declaration but no implementation. A variable is nothing but a name given to a storage area that our programs can manipulate. Each variable in Objective-C has a specific type, which determines the size and layout of the variable's memory; the range of values that can be stored within that memory; and the set of operations that can be applied to the variable.

Instance and Class Members, Objects, Classes, and Interfaces You can access an object's instance variables from an object as described in Using Objects. Instance variables are in constrast to class variables (which you declare using the static modifier). The runtime� Instance variables represent an implementation detail, and should typically not be accessed outside of the class itself. Moreover, you can declare them in the implementation block or synthesize them using declared properties. Typically you should not, therefore, declare instance variables in the public interface and so you should omit the braces.

Comments
  • There's no such thing as an instance variable in an interface. There are constants, basically...
  • In other words, they are class variables, not instance variables.
  • possible duplicate of Why are interface variables static and final by default?
  • Ya sure there are constant, but my question is what is use of constant class variable in interface