Java object-oriented understanding problem [duplicate]

Question

This is my first class

public class DigitalDevice {
    public int abc = 1;
}

And this is my second class

public class SmartPhone extends DigitalDevice {

    SmartPhone() {
        abc = 2;
        super.abc=3;
        DigitalDevice.abc=4;
        
    }
}

In the SmartPhone class, when I recall abc, DigitalDevice's abc is accessible and changeable, and when I recall super.abc, also DigitalDevice's abc is accessible and changeable, but when I recall DigitalDevice.abc, DigitalDevice's abc is not accessible and changeable and the IDE gives and error and asks for making abc static in the DigitalDevice class.

Is this true that in SmartPhone class abc is super.abc is DigitalDevice.abc?

Your code does not compile. Before posting here, get your code to the point of compiling or ask a question about a specific point where it fails to compile. — Basil Bourque
– Basil Bourque, Commented Aug 31, 2024 at 23:17
Before posting here, study The Java Tutorials provided by Oracle free of cost. See the page on static member fields, with regard to DigitalDevice.abc. — Basil Bourque
– Basil Bourque, Commented Aug 31, 2024 at 23:18

Progman · Accepted Answer · 2024-08-31 20:18:07Z

4

No, it is not true. abc and super.abc is the same, as well as this.abc (not used in your code). But DigitalDevice.abc is an attempt to call a static field named abc in the class DigitalDevice. There is no such static field in that class and your IDE is rightfully telling you that. Check When to use static/non-static variable in JAVA on what the difference between static and non-static is.

answered Aug 31, 2024 at 20:18

Progman

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3 Comments

Behnam R Over a year ago

so why do i when change abc in smartPhone class, abc in digitalDevice class changes also? after changing abc in smartPhone class when i print abc and super.abc, they are same value, how do i changed a non static var ?

Progman Over a year ago

@BehnamR There is only one public field abc, which is inherited to the SmartPhone class. The code abc, super.abc and this.abc reference the same field of your SmartPhone instance.

JohnnyD Over a year ago

To clarify further, a class and an object are not the same thing. An object is an instance of a class. To use an analogy, a "class" can be likened to a blueprint for a phone, while an object is the actual phone itself. Therefore, a static property or method can only be called from the class (the blueprint), such as SmartPhone.anyStaticProperty. In contrast, a non-static property or method can only be called from an instance of the class, like SmartPhone smartPhone = new SmartPhone(); smartPhone.abc

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