cap.round和cap.butt有什么区别

import javax.swing.*;
import java.awt.*;
import java.awt.geom.*;
public class Example6_5 extends JFrame
{
public Example6_5()
{
super("设置线条粗细");
setSize(180,180);
setVisible(true);
setDefaultCloseOperation(EXIT_ON_CLOSE);
}
public static void main(String[] args)
{
new Example6_5();
}
public void paint(Graphics g)
{
Graphics2D g_2d=(Graphics2D)g;
Line2D line_1=new Line2D.Double(50,50,120,50);
Line2D line_2=new Line2D.Double(50,80,120,80);
Line2D line_3=new Line2D.Double(50,110,120,110);
BasicStroke bs_1=new BasicStroke(16,BasicStroke.CAP_BUTT,BasicStroke.JOIN_BEVEL);
BasicStroke bs_2=new BasicStroke(16f,BasicStroke.CAP_ROUND,BasicStroke.JOIN_MITER);
BasicStroke bs_3=new BasicStroke(16f,BasicStroke.CAP_SQUARE,BasicStroke.JOIN_ROUND);
g_2d.setStroke(bs_1);
g_2d.draw(line_1);
g_2d.setStroke(bs_2);
g_2d.draw(line_2);
g_2d.setStroke(bs_3);
g_2d.draw(line_3);
}
}