Reference type variable "this"

It indicates instance itself.

can use in instance method and constructor! (CANNOT use in static method(class method))

To distinguish local variable and instance variable

class Car {
    //instance variable
    String color;
    String gearType;
    int door;
    
    Car(String color, String gearType, int door) {
        //instance variable this.____
        //this.color <=> Car.color
        this.color = color;
        this.gearType = gearType;
        this.door = door;
    }
}

example :

class MyMath2 {
    //instance variable
    long a,b;//this.a, this.b
    
    //can use instance method and constructor only!
    MyMath2(int a, int b) {//constructor
        //distinguish iv(instance variable) and lv(local variable)
        this.a = a;
        this.b = b;
    }
    MyMath2() {
        return a+b;//return this.a + this.b;
    }
    //static method(class method)
    //without creating object.
    //CANNOT use iv.
    //CANNOT use this which indicate object itself!
    static MyMath2(long a, long b) {//local variable
        return a+b;
    }
    
}