Java 数据的定义位置

脚踏实地 2013-10-29 08:27:29

import java.awt.*;

import java.awt.geom.*;

import javax.swing.*;

class DrawJPanel extends JPanel

{

	public void paintComponent(Graphics g)

	{	

		super.paintComponent(g);

		Graphics2D g2 = (Graphics2D)g;



		

		

		Rectangle2D rect = new Rectangle2D.Double(top_x,top_y,WIDTH,HEIGHT);

		g2.draw(rect);



		Ellipse2D ellipse = new Ellipse2D.Double(top_x,top_y,WIDTH,HEIGHT);

		ellipse.setFrame(rect);

		g2.draw(ellipse);

		

		Line2D line = new Line2D.Double(new Point2D.Double(top_x,top_y),new Point2D.Double(top_x+WIDTH,top_y+HEIGHT));

		g2.draw(line);



		



		Ellipse2D circle = new Ellipse2D.Double();

		circle.setFrameFromCenter(centerX,centerY,centerX+radius,centerY+radius);

		

		g2.draw(circle);

		  

	   	double centerX = rect.getCenterX();

	    double centerY = rect.getCenterY();

	    double radius = 150;

	    double top_x = 200;

	    double top_y = 150;

	    double WIDTH = 200;

	    double HEIGHT = 100;

	   	  

	}	

	    

	    

}

class DrawJFrame extends JFrame

{

	public DrawJFrame()

    {

		setTitle("SHAPE");

		setSize(Frame_WIDTH,Frame_HEIGHT);

		DrawJPanel panel = new DrawJPanel();

		add(panel);

	}

	public static final int Frame_WIDTH = 800;

	public static final int Frame_HEIGHT = 600;

}

class DrawTest

{

	public static void main(String[] args)

	{

		DrawJFrame frame = new DrawJFrame();

		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

		frame.setVisible(true);

	}

}

求助大神这个为什么运行会报错

而这个不会报错

import java.awt.*;

import java.awt.geom.*;

import javax.swing.*;

class DrawJPanel extends JPanel

{

	public void paintComponent(Graphics g)

	{	

		super.paintComponent(g);

		Graphics2D g2 = (Graphics2D)g;



		double top_x = 200;

	    double top_y = 150;

	    double WIDTH = 200;

	    double HEIGHT = 100;

		

		Rectangle2D rect = new Rectangle2D.Double(top_x,top_y,WIDTH,HEIGHT);

		g2.draw(rect);



		Ellipse2D ellipse = new Ellipse2D.Double(top_x,top_y,WIDTH,HEIGHT);

		ellipse.setFrame(rect);

		g2.draw(ellipse);

		

		Line2D line = new Line2D.Double(new Point2D.Double(top_x,top_y),new Point2D.Double(top_x+WIDTH,top_y+HEIGHT));

		g2.draw(line);



		double centerX = rect.getCenterX();

	    double centerY = rect.getCenterY();

	    double radius = 150;



		Ellipse2D circle = new Ellipse2D.Double();

		circle.setFrameFromCenter(centerX,centerY,centerX+radius,centerY+radius);

		//circle.setFrameFromCenter(300,200,450,350);

		g2.draw(circle);

		  

	  

	}	

	    

	    

}

class DrawJFrame extends JFrame

{

	public DrawJFrame()

    {

		setTitle("SHAPE");

		setSize(Frame_WIDTH,Frame_HEIGHT);

		DrawJPanel panel = new DrawJPanel();

		add(panel);

	}

	public static final int Frame_WIDTH = 800;

	public static final int Frame_HEIGHT = 600;

}

class DrawTest

{

	public static void main(String[] args)

	{

		DrawJFrame frame = new DrawJFrame();

		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

		frame.setVisible(true);

	}

}

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MiceRice 2013-10-29

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写错地方了吧？常量必须在函数外面、类里面进行定义。

脚踏实地 2013-10-29

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引用 1 楼 ldh911 的回复:

Rectangle2D rect = new Rectangle2D.Double(top_x, top_y, WIDTH, HEIGHT); 至少在使用其作为参数之前，这两个变量的值，你要先声明吧？

但我在第一个程序中把它们定义成常量位置不变 public static final double top_x = 200; public static final double top_y = 150; public static final double WIDTH = 200; public static final double HEIGHT = 100; 为什么还是会报错？

MiceRice 2013-10-29