Define member variable description in Java interface

First you need to understand what the interface means. An interface is a uniform ' protocol ', and the attributes in the interface are members of the ' protocol '. They are public, static, and final constants. Equivalent to a global constant.

The variables inside the interface are public static final. So you can write this:

public static final int i=10;

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int i=10; (You can omit a part, the member variable in the interface defaults to public static final)

Notice that the variable is given an initial value at the time of declaration.

Explain:

First you need to understand what the interface means. An interface is a uniform ' protocol ', and the attributes in the interface are members of the ' protocol '. They are public, static, and final constants. Equivalent to a global constant.

An abstract class is a class that is not ' complete ', equivalent to an interface and a middle layer of a concrete class. That is, to satisfy the abstraction of the interface and to satisfy the concrete implementation.

If an interface can define a variable, but the method in the interface is abstract, the property cannot be modified by behavior in the interface. Some people will say, no relationship, you can modify the properties of an interface by implementing the behavior of the interface's objects. This is of course not a problem, but consider such a situation. If interface A has a static variable A that has public access permissions. According to Java semantics, we can change the value of variable A in the interface without accessing the variable A through the object that implements the interface, through a.a = xxx; As can be done in an abstract class, all objects that implement interface A will automatically have the value of the changed a, which means that a place has changed a, and the value of a in all these objects has changed. What is the difference between this and the abstract class, how to embody the higher level of abstraction of the interface, how to embody the unified protocol provided by the interface, that also interface this abstraction to do? Therefore, the interface can not appear in the variable, if there are variables, and the interface provided by the unified abstraction of the idea is inconsistent. Therefore, the attribute in the interface must be constant, can only be read and cannot be changed, so as to provide a uniform property for the object that implements the interface.

In layman's words, what you think is to change is put in your own implementation, not in the interface, interface is just a kind of things of the properties and behavior of a higher level of abstraction. For the modification to close, the extension (different implementation implements) Open, interface is a manifestation of the principle of closure.

Define member variable description in Java interface