CODEWITHSUNDEEP
javavariablesstatic
SERich
SERich

Reputation: 653

Can static method access non-static instance variable?

So my understanding was that you can't use static method to access non-static variables, but I came across following code.

class Laptop {
  String memory = "1GB";
}
class Workshop {
  public static void main(String args[]) {
    Laptop life = new Laptop();
    repair(life);
    System.out.println(life.memory);
    }
  public static void repair(Laptop laptop) {
    laptop.memory = "2GB";
  }
}

Which compiles without errors.

So isn't 

public static void repair(Laptop laptop) {
laptop.memory = "2GB";
}

accessing String memory defined in class Laptop, which is non-static instance variable?

Since the code compiles without any error, I'm assuming I'm not understanding something here. Can someone please tell me what I'm not understanding?

Upvotes: 12

Views: 42649

Answers (5)

Govinda Hinduja
Govinda Hinduja

Reputation: 29

Yes, a non-static method can access a static variable or call a static method in Java. There is no problem with that because of static members

i.e. both static variable and static methods belongs to a class and can be called from anywhere, depending upon their access modifier.

For example, if a static variable is private then it can only be accessed from the class itself, but you can access a public static variable from anywhere.

Similarly, a private static method can be called from a non-static method of the same class but a public static method e.g. main() can be called from anywhere

Upvotes: 0

VRadhe
VRadhe

Reputation: 569

try this code 

public static void repair() {

    Laptop laptop =new Laptop();

    laptop.memory="2GB";

  }

Upvotes: -2

Arun Raaj
Arun Raaj

Reputation: 1800

Static methods cannot modify their value. You can get their current value by accessing them with the reference of current class.

Upvotes: 0

Thomas
Thomas

Reputation: 88707

A static method can access non-static methods and fields of any instance it knows of. However, it cannot access anything non-static if it doesn't know which instance to operate on.

I think you're mistaking by examples like this that don't work:

class Test {
  int x;

  public static doSthStatically() {
    x = 0; //doesn't work!
  }
}

Here the static method doesn't know which instance of Test it should access. In contrast, if it were a non-static method it would know that x refers to this.x (the this is implicit here) but this doesn't exist in a static context.

If, however, you provide access to an instance even a static method can access x.

Example:

class Test {
  int x;
  static Test globalInstance = new Test();

  public static doSthStatically( Test paramInstance ) {
    paramInstance.x = 0; //a specific instance to Test is passed as a parameter
    globalInstance.x = 0; //globalInstance is a static reference to a specific instance of Test

    Test localInstance = new Test();
    localInstance.x = 0; //a specific local instance is used
  }
}

Upvotes: 34

Bhargav Kumar R
Bhargav Kumar R

Reputation: 2200

You can access only with object reference.

Instance variables defined at class level, have to be qualified with object name if you are using in a static context. But it does not not mean that you cannot access at all.

Upvotes: 0

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