In Java, the distinction between instance methods and static methods lies in their relationship with objects of a class. In simple terms, instance methods belong to an object (an instance of a class), while static methods belong to the class itself.

Here's a breakdown of the key differences:

Instance Methods

Instance methods are the more common type of method in Java. They operate on the specific state of an individual object.

• Association: Tied to a specific instance of a class.
• Invocation: You must create an object of the class before you can call an instance method.
• Access: Can access both instance variables (specific to each object) and static variables (shared among all objects).
• this keyword: Can use the this keyword, which refers to the current object.

When to Use Instance Methods

Use instance methods when the method's logic depends on the individual characteristics of an object. For example, a Car class might have instance methods like startEngine() or getSpeed(), as these actions are specific to a particular car.

Example:

class Dog {
    String name;

    public void bark() {
        System.out.println(name + " says woof!");
    }
}

public class Main {
    public static void main(String[] args) {
        Dog myDog = new Dog();
        myDog.name = "Buddy";
        myDog.bark(); // Calling an instance method on a Dog object
    }
}

Static Methods

Static methods, also known as class methods, are not tied to any specific object. They are associated with the class as a whole.

• Association: Belongs to the class, not to any particular instance.
• Invocation: Can be called directly on the class name, without creating an object.
• Access: Can only access static variables and other static methods directly. They cannot directly access instance variables or instance methods.
• this keyword: Cannot use the this keyword because there is no specific object to refer to.

When to Use Static Methods

Use static methods for utility functions that don't rely on the state of a particular object. The Math class in Java is a great example; all its methods, like Math.max() and Math.sqrt(), are static because they perform calculations that are independent of any specific object.

Example:

class Calculator {
    public static int add(int a, int b) {
        return a + b;
    }
}

public class Main {
    public static void main(String[] args) {
        int sum = Calculator.add(5, 3); // Calling a static method on the Calculator class
        System.out.println("The sum is: " + sum);
    }
}

Summary of Key Differences

This video provides a clear and concise explanation of the difference between static and non-static (instance) variables and methods in Java, which can be very helpful for beginners. Video Tutorial on Static vs Non-Static in Java