Instance Members & Static Members

Instance Members → non-static members

Instance Variables & Methods (Members)

Instance variables and methods belong to individual instances of a class. Each object has its own set of instance members that may have different values.

public class BankAccount {
    int total;

    public void getTotal() {
        System.out.println(total);
    }
}

BankAccount accountOne = new BankAccount();
BankAccount accountTwo = new BankAccount();

accountOne.total = 30;  // Instance variable
accountTwo.total = 60;

accountOne.getTotal();  // Outputs 30
accountTwo.getTotal();  // Outputs 60

• Instance members require an instance of the class to access and modify variables or methods.

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Keyword: this

• this is a keyword used to refer to the current instance of a class.
• Useful when a method’s parameter has the same name as an instance field.

public class Car {
    String color;

    public Car(String color) {
        this.color = color;  // "this.color" refers to the instance field, not the parameter
    }
}

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Static Variables & Methods (Members)

• Static variables and methods belong to the class itself, not to any instance. All objects share the same static members.

• Static members are shared across all instances of a class.

public class Car {
    static int numberOfCars;

    public Car() {
        numberOfCars++;
    }
}

Car carOne = new Car();
Car carTwo = new Car();

System.out.println(Car.numberOfCars);  // Outputs 2

Things to consider when using static members

• Static methods cannot use instance fields or methods.
• Static methods cannot access the keyword this, because they are not associated with any instance.