Implementing fillCircle with parameters

Since our fillCircle method always fills circles of same size in the center of the board, it would be nice if we could have it draw different size circles centered at an x-y coordinate that we specify. This is exactly what parameters accomplish for us. The three parameters that we would need are the radius, and the x- and y- coordinates, all of which we specify in the method header. The method invocation, correspondingly, would now include 3 arguments to match the three parameters:

Board b = new Board(50,50);

// now fill circle with radius 10 centered at coordinate (25,30)

b.fillCircle(10, 25, 30);

With the three parameters that we specified, fillCircle looks like:

// this code would go in the Board class definition in BaseBoard.java

public void fillCircle(int radius, int xOrigin, int yOrigin)

{

// obtain the board object’s dimensions

int rows = this.getRows();

int cols = this.getCols();

for (int y = 0; y < rows; y++)

{

for (int x = 0; x < cols; x++)

{

if ((y – yOrigin)*(y - yOrigin) + // condition continued

(x – xOrigin)*(x – xOrigin) <= radius*radius)

this.fillCell(x, y, Color.red);

}

}

}

The relationship between arguments in a method invocation and parameters in its header is key to understanding how methods work. When the statement b.fillCircle(10, 25, 30) executes, Java copies the values of the arguments 10, 25, and 30 to the parameters in the method header radius, xOrigin, yOrigin, respectively. The parameters act as variables that are local to the method. Next, the statements inside fillCircle execute. Finally when the method is finished, the statement after b.fillCircle(10, 25, 30) executes. Keep in mind that the method invocation and the method implementation are in different files.

// Method invocation in CircleTest.java copies the values of the arguments to the parameters

b.fillCircle(10, 25, 30);

// Method definition in BaseBoard.java

public void fillCircle(int radius, int xOrigin, int yOrigin)

// Inside fillCircle, the value of radius is 10,

// xOrigin 25, and yOrigin 30

There’s important things to recognize here. We now have two methods both named the same thing (fillCircle), but each takes on a different number of parameters. In programming language terms, this is referred to as method overloading. A method is overloaded when we define it two or more times (with the same method name), but each of the definitions has a different signature (go back and look up what signature means). This is convenient since we can draw square differently by specifying or not specifying parameters, but the method name is the same.