I'm trying to implement a Factory pattern in Java. I have a class called Shape which Circle and Triangle extends. The problem is that Shape constructor gets only 2 parameters while Circle gets 3 parameters and so is Triangle (which I won't show in the code section because is identical to Circle). To demonstrate it better:
private interface ShapeFactory{
public Shape create(int x, int y);
}
private class CircleFactory implements ShapeFactory{
public Shape create(float radius, int x, int y){ //error
return new Circle(radius, x,y);
}
}
Any ideas how to overcome this problem? I must not recieve an input from user inside the factory (must be recieved from outside).
Thanks!
You have two options:
1) Abstract Factory:
RectangularShape extends Shape
RoundShape extends Shape
and RectangularShapeFactory
and RoundShapeFactory
2) Builder (see also Item 2 in Effective Java)
public Shape {
private final int x;
private final int y;
private final double radius;
private Shape(Builder builder) {
x = builder.x;
y = builder.y;
radius = builder.radius;
}
public static class Builder {
private final int x;
private final int y;
private double radius;
public Builder(int x, int y) {
this.x = x;
this.y = y;
}
public Builder radius(double radius) {
this.radius = radius;
return this;
}
public Shape build() {
return new Shape(this);
}
}
}
//in client code
Shape rectangle = new Shape.Builder(x,y).build();
Shape circle = new Shape.Builder(x,y).radius(radiusValue).build();