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Passing Object as Parameter in Java

Passing Object as Parameter 

Passing Object Example


class BOX {
    int height;
    int width;

    BOX(int h, int w) {            // parameterized constructor
        height = h;
        width = w;
    }

    void area(BOX b1) {            // area function having object b1 in parameter
        int areabox = b1.height * b1.width; // initialize areabox having product result
        System.out.println("Area of Box : " 
                                + areabox);
    }
}

class BoxExample {
    public static void main(String args[]) {
        BOX b1 = new BOX(10, 20);        // constructor calling with parameter
        b1.area(b1);    // calling fuction with object
    }
}
Output of the program :
Area of Box : 200

Explanation :

  1. We can pass Object of any class as parameter to a method in java.
  2. We can access the instance variables of the object passed inside the called method.
areabox = b1.height * b1.width
  1. It is good practice to initialize instance variables of an object before passing object as parameter to method otherwise it will take default initial values.

Different Ways of Passing Object as Parameter :

1 : By directly passing Object Name

class BOX {
    int height;
    int width;

    BOX(int h, int w) {            // parameterized constructor
        height = h;
        width = w;
    }

void area(BOX b1) {
        int areaOfBox = b1.height * b1.width;
        System.out.println("Area of Box : " 
                                + areaOfBox);
    }

class BoxExample {
    public static void main(String args[]) {
        BOX b1 = new BOX(10, 20);
        b1.area(b1);
    }

2 : By passing Instance Variables one by one


class BOX {
    int height;
    int width;

    void area(int height, int width) {
        int areaOfBox = height * width;
        System.out.println("Area of Box : "
                    + areaOfBox);
    }
}

class BoxExample {
    public static void main(String args[]) {
        BOX r1 = new BOX();
        BOX r2 = new BOX();

        b1.height = 20;
        b1.width = 10;

        r2.area(b1.height, b1.width);
    }
}
Actually this is not a way to pass the object to method. but this program will explain you how to pass instance variables of particular object to calling method.

3 : We can pass only public data of object to the Method.

Suppose we made width variable of a class private then we cannot update value in a main method since it does not have permission to access it.
private int width;
after making width private –
class BOXExample {
    public static void main(String args[]) {
        BOX b1 = new BOX();
        BOX b2 = new BOX();

        b1.height = 20;
        b1.width = 10;        //it is not access because width is private

        b2.area(b1.height, b1.width);
    }
}
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