// Test2.java
import java.awt.Graphics;
import javax.swing.JPanel;
import javax.swing.JFrame;


class Panel4 extends JPanel
{

    Line2 line[];
    Vec2 pts[];
    Line2 perp_line;
    
    public Panel4()
    {
	line = new Line2[3];
	line[0] = new Line2(-0.3,-0.5,-0.7,0.9);
	line[1] = new Line2();
	line[1].from(0.5,-0.5).away(0.8,60.0);
	Vec2 a = new Vec2(-0.4,0.5);
	Vec2 b = new Vec2(0.6, 0.8);
	line[2] = new Line2(a,b);
	pts = new Vec2[1];
	pts[0] = new Vec2(-1.4,-0.2);
	double s = line[0].getClosestPosition(pts[0]);
	perp_line = new Line2(pts[0], line[0].lerp(s));
    }
    public void paintComponent(Graphics g)
    {
	super.paintComponent( g );
	// world/screen transformation
	Vec2.xoffset = getWidth()/2;
	Vec2.yoffset = getHeight()/2;
	int resx = getWidth()/4;
	int resy = getHeight()/3;
	Vec2.Resolution = (resx<resy? resx: resy);
	// Here are our objects
	//for (int i=0; i<line.length; i++) line[i].draw(g);
	for (int i=0; i<line.length; i++)
	    Arrow.draw(line[i],g,1.0,Arrow.AH_FILLED);
	for (int j=0; j<pts.length; j++) pts[j].draw(g);
	perp_line.draw(g);
	// Coordinate origin
	Vec2 origin = new Vec2(0,0);
	int [] iv = origin.convert();
	int size = 5;
	g.drawLine(iv[0]-size,iv[1]-size,iv[0]+size,iv[1]+size);
	g.drawLine(iv[0]-size,iv[1]+size,iv[0]+size,iv[1]-size);
    }
}

public class Test4
{

    public static void test1()
    {
	Vec2 a = new Vec2(14,20);
	Vec2 b = new Vec2(4,-3);
	Vec2 c = new Vec2(6,8);
	Vec2 d = new Vec2(-8,4);

	Line2 AB = new Line2(a,b);
	Line2 CD = new Line2(c,d);


	System.out.println( "line AB: " + AB );
	System.out.println( "line CD: " + CD );
	System.out.println( "line AB + Vec2(1,-1): " + AB.translate(1.0,-1.0) );

	System.out.println( "length AB : " + AB.length() );
	System.out.println( "angle(AB,CD) : " + Line2.angle(AB,CD) );

	Line2 XY = new Line2();
	System.out.println( "XY.from(0,1).to(3,2): " + XY.from(0,1).to(3,2) );
	System.out.println( "XY.to(a).from(b): " + XY.to(a).from(b) );

	Vec2 angled = new Vec2(30.0);
	System.out.println( "angled = Vec2(30.0): " + angled );
	System.out.println( "Line2(1,2,3,4): " + new Line2(1,2,3,4) );
	Line2 R1 = new Line2(angled);
	System.out.println( "R1 = Line2(30.0)): " + R1 );

	Line2 R2 = new Line2();
	R2.from(1,1).away(1.0,-90.0);
	System.out.println( "R2.from(1,1).away(1.0,-90.0) " + R2 );
	System.out.println("test 1 done.");

    }

    public static void main(String args[] )
    {
	Panel4 panel = new Panel4();
	for (int i=0; i<args.length; i++) {
	    String str = String.format("arg[%d] %s",i,args[i]);
	    System.out.println(str);
	}
	if (args.length>0 && args[0].equals("1"))
	{
	    test1();
	    return;
	}
	JFrame application = new JFrame("Test4");
	application.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	application.add(panel);
	application.setSize(200,200);
	application.setVisible(true);
    }
}

Results

When run with the first command argument of "1", the program generates some validation tasks to test various aspects of the Line2 class.

C:\classes\ece538\java>java Test4 1 abc def
arg[0] 1
arg[1] abc
arg[2] def
line AB: [14.0 20.0]:[4.00 -3.00]
line CD: [6.00 8.00]:[-8.00 4.00]
line AB + Vec2(1,-1): [15.0 19.0]:[5.00 -4.00]
length AB : 25.079872407968907
angle(AB,CD) : -50.556038423125045
XY.from(0,1).to(3,2): [0.00 1.00]:[3.00 2.00]
XY.to(a).from(b): [4.00 -3.00]:[14.0 20.0]
angled = Vec2(30.0): [0.866 0.500]
Line2(1,2,3,4): [1.00 2.00]:[3.00 4.00]
R1 = Line2(30.0)): [0.00 0.00]:[0.866 0.500]
R2.from(1,1).away(1.0,-90.0) [1.00 1.00]:[1.00 0.00]
test 1 done.

When the first argument is not "1", a test of the graphics display and other validation constructions is displayed.