Java Keywords

static

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• Fields and methods declared with the static keyword belong to the class itself rather than to instances of the class. This allows us to use these class members without creating an object of the class. Static fields and methods are initialised and stored in the method area (part of the heap) during the class-loading phase, which occurs before the main program execution begins

A non-static variable or method cannot be referenced from a static context

When a static context is established (e.g., within a static method), it has no associated object instance. Therefore, it cannot access non-static members, as they don’t yet exist or may not exist at all. Attempting to reference a non-static member in a static context typically results in a compilation error.

In essence, trying to call a non-static variable or method from a static context is like trying to use something that hasn’t been built yet.

final

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• On OOP Class: prevents Inheritance
• On method: prevents Method Overriding
• On variable: makes it a constant (prevents modification after initialisation)

The following code can compile & run!

final int x;
if (true) {
 x = 10;

} else x = 20;

It works because `final int x` isn't initialised yet, and the if/else statement ensures only one initialisation will take place.

extends

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• The extends keyword establishes an “is-a” relationship from the subclass to the superclass, enabling inheritance