Accepting and Returning Objects when Programming with Methods in Java

This section will explain the coding listed in the previous section.  Let us start with the following:

    int x=0;
    int y=0;

You can observe that I declared three fields/attributes for the class “MyCalc.” And the following is the new “method” I introduced:

    public void copyValues(MyCalc c) {
        x = c.x;
        y = c.y;
    }

The above method is named “copyValues” and it returns the “void” type.  The “void” indeed is simply “nothing.” In other words, the method “calcSum” doesn’t return any value after its execution.   

The most important issue is the parameter we are required to pass to it.  The parameter which it accepts must be of type “MyCalc.”  That means I need to create an object of type “MyCalc” (in the calling program), fill it with values and finally call this method (“copyValues”) by passing the same object.  The object which is passed from the calling program will be referred to as “c.” 

You can observe that “c” is of type “MyCalc.”  That means it is an object which is equipped with all the members of the class “MyCalc.” Once the object is received from the calling program, the runtime executes the following statements:

        x = c.x;
        y = c.y;

The above statements simply assign the values available in “c” to the current object which is executing this method.

Now, if we proceed to our “test” frame, we have the following initially:

        MyCalc obj1 = new MyCalc();
        MyCalc obj2 = new MyCalc();

        obj1.x = 10;
        obj1.y = 20;

I declared two objects named “obj1” and “obj2.” Now, both of them internally contain members (x, y, copyValues, getSum).  You can also observe that I am simply providing the values of “x” and “y” for only “obj1.” Proceeding further, we have the following:

        obj2.copyValues(obj1); 

The above is the most important statement of our example.  I am calling the method “copyValues” from “obj2” (where x and y in that object are not assigned with any values yet), by passing “obj1.”  The object which is being passed (“obj1”) will be referred to as “c” by the method “copyValues.” During the execution of the method “copyValues,” the values of “x” and “y” belonging to “c” will be assigned to “x” and “y” of “obj2” as the “copyValues” is being executed from “obj2.” Proceeding further, we have the following:

        int r;
        r = obj1.getSum();
        this.lblMsg.setText("Sum = " + String.valueOf(r));

        r = obj2.getSum();
        this.lblMsg2.setText("Sum = " + String.valueOf(r));

The above code dues nothing but get the sum of “x” and “y” and display it. My previous article gives you a better understanding of this.