Java keywords static, final, super, and this

1. static

• Purpose: Makes a member (variable or method) belong to the class rather than an instance.
• Usage:
  • Static variable: shared across all instances of the class.
  • Static method: can be called without creating an object.
• Example:

class Example {
    static int count = 0; // shared by all objects
    static void showCount() {
        System.out.println(count);
    }
}

Example.showCount(); // Access without creating object

class Example {
    static int count = 0; // shared by all objects
    static void showCount() {
        System.out.println(count);
    }
}

Example.showCount(); // Access without creating object

2. final

• Purpose: Makes a variable, method, or class unchangeable or non-overridable.
• Usage:
  • Final variable: value cannot be changed once assigned.
  • Final method: cannot be overridden by subclasses.
  • Final class: cannot be subclassed.
• Example:

final int MAX = 100; // value cannot change

final class MyClass {} // cannot be extended

class Parent {
    final void display() { System.out.println("Hello"); }
}

final int MAX = 100; // value cannot change

final class MyClass {} // cannot be extended

class Parent {
    final void display() { System.out.println("Hello"); }
}

3. super

• Purpose: Refers to the parent class of the current object.
• Usage:
  • Access parent class methods overridden in the child class.
  • Access parent class constructor.
• Example:

class Parent {
    void show() { System.out.println("Parent"); }
}

class Child extends Parent {
    void show() {
        super.show(); // call parent method
        System.out.println("Child");
    }
}

class Parent {
    void show() { System.out.println("Parent"); }
}

class Child extends Parent {
    void show() {
        super.show(); // call parent method
        System.out.println("Child");
    }
}

4. this

• Purpose: Refers to the current object.
• Usage:
  • Access instance variables when shadowed by method/constructor parameters.
  • Call another constructor in the same class.
• Example:

class Example {
    int x;
    Example(int x) {
        this.x = x; // distinguish between instance and parameter
    }
    void show() {
        System.out.println(this.x);
    }
}

class Example {
    int x;
    Example(int x) {
        this.x = x; // distinguish between instance and parameter
    }
    void show() {
        System.out.println(this.x);
    }
}

✅ Quick summary: