I have multiple classes, they are Circle, Square, ObjectList and ShapePictureDri
ID: 3814019 • Letter: I
Question
I have multiple classes, they are Circle, Square, ObjectList and ShapePictureDriver. I try to create 2 objects from Circle and 2 objects from Square. I create two methods draw() which output the shape to the console ( "[]" represents a square and "O" represents a circle). I want to print out the shape of the objects I added to ObjectList as shown in ShapePictureDriver. How to write the method toString() in ObjectList?
class ObjectList {
private Circle[] myCircles = new Circle[100];
private int numCircles;
private Square[] mySquares = new Square[100];
private int numSquares;
public void addCircle(Circle circle) {
myCircles[numCircles++] = circle;
}
public void addSquare(Square square) {
mySquares[numSquares++] = square;
}
public String toString() {
//hints:
//need to loop over Circles first
//then another loop over Squares
//this approach is nonscalable!
}
}
public class Square
{
private int x;
private int y;
String shape = "[]";
public Square(int nx, int ny){
x=nx;
y=ny;
}
public void draw(){
System.out.println(shape);
}
}
public class ShapesPictureDriver {
public static void main(String[] args) {
Square firstSquare = new Square(3,4);
Square secondSquare = new Square(10,20);
Circle firstCircle = new Circle(1,5,3);
Circle secondCircle = new Circle(2,10,6);
ObjectList picture = new ObjectList();
picture.addSquare( firstSquare );
picture.addSquare( secondSquare );
picture.addCircle( firstCircle );
picture.addCircle( secondCircle );
System.out.println( "Drawing a Picture with Circles and Squares: " );
System.out.println(picture.toString());
}
}
Explanation / Answer
I assume that similar to Square class, there will be a member String shape = "O"; in circle class(default membwer, not private), which shows the shape of the circle. Then, the toString method can be implemented as below..
class ObjectList {
private Circle[] myCircles = new Circle[100];
private int numCircles;
private Square[] mySquares = new Square[100];
private int numSquares;
public void addCircle(Circle circle) {
myCircles[numCircles++] = circle;
}
public void addSquare(Square square) {
mySquares[numSquares++] = square;
}
public String toString() {
// as we have to return the string from this method,
// we cannot use the draw() method in square or circle
// class. because they don't return anything.
// we need to loop on all objecs, and prepare the
// output string ourselves.
String s = "";
s += "Printing Circles: ";
for(int i=0; i<numCircles; i++) {
Circle c = myCircles[i];
s += c.shape + " ";
}
s += "Printing Squares: ";
for(int i=0; i<numSquares; i++) {
Square sq = mySquares[i];
s += sq.shape + " ";
}
// return the result String
return s;
}
}