Example

interface Shape
{
    Shape setWidth(int value);
    Shape setHeight(int value);

    int getWidth();
    int getHeight();
}

class Rect implements Shape {
    private final int width;
    private final int height;
    public Rect(int width, int height) {
        this.width = width;
        this.height = height;
    }
    @Override public Shape setWidth(int value) {
        return new Rect(value, height);
    }
    @Override public Shape setHeight(int value) {
        return new Rect(width, value);
    }
    @Override public int getWidth() {
        return width;
    }
    @Override public int getHeight() {
        return height;
    }
}

class Square implements Shape {
    private final int size;
    public Square(int size) {
        this.size = size;
    }
    @Override public Shape setWidth(int value) {
        if (value != size){
            return new Rect(value, size);
        }
        return this;
    }
    @Override public Shape setHeight(int value) {
        if (value != size){
            return new Rect(size, value);
        }
        return this;
    }
    @Override public int getWidth() {
        return size;
    }
    @Override public int getHeight() {
        return size;
    }
}