为什么该程序无法绘制正方形？

Question

I am currently learning out of Computing Concepts with java 2 essentials by Cay Hortmans, And i copied this program straight from the book, yet it is not working. Im not looking for an entirely separate way of doing this, but just why this code, straight from the book, is not drawing the square correctly.

import java.applet.*;
import java.awt.*;
import javax.swing.JOptionPane;

public class ColorSelect extends Applet{

    private static final long serialVersionUID = -7954365679431207534L;

    public void init(){
        String input; //ask the user for red, green, blue values

        input = JOptionPane.showInputDialog("Red:");
        float red = Float.parseFloat(input);

        input = JOptionPane.showInputDialog("Green:");
        float green = Float.parseFloat(input);

        input = JOptionPane.showInputDialog("Blue:");
        float blue = Float.parseFloat(input);
        fillColor = new Color(red, green, blue);
    }

    public void paint(Graphics g){
        final int SQUARE_LENGTH = 100;

        Graphics2D g2 = (Graphics2D)g;

        //select color into graphics content

        g2.setColor(fillColor);

        //construct and fill a square whose center is the center of the window

        Rectangle square = new Rectangle(
                (getWidth() - SQUARE_LENGTH) / 2,
                (getHeight() -  SQUARE_LENGTH) / 2,
                SQUARE_LENGTH,
                SQUARE_LENGTH);

        g2.fill(square);
    }
    private Color fillColor;
}

Answer 1

Because your r , g , b values are all float s, you are invoking the Color constructor that has 3 float parameters: http://docs.oracle.com/javase/7/docs/api/java/awt/Color.html#Color(float , float, float)

Creates an opaque sRGB color with the specified red, green, and blue values in the range (0.0 - 1.0). Alpha is defaulted to 1.0. The actual color used in rendering depends on finding the best match given the color space available for a particular output device.

Either change your r, g, b types to int or cast to int

Answer 2

抱歉，伙计们，我意识到在估算时我使用的是int值而不是float，这很糟糕。

Answer 3

Rectangle specifies bounds of two opposite corners just as fill() wants. You need

Rectangle square = new Rectangle(
                                  (getWidth()/2 - SQUARE_LENGTH/2),
                                  (getHeight()/2 -  SQUARE_LENGTH/2),
                                  (getWidth()/2 + SQUARE_LENGTH/2),
                                  (getHeight()/2 +  SQUARE_LENGTH/2)
                                );