Drawing on a Jframe from two different classes

I am trying to create a program that record mouse clicks, draw lines between those points and after some calculations display some circles through a button call. My problem is that I can display the lines or the circles, but not both.

I know there is something overlapping something else, but I am very new to Java and I don't know how to fix it. Here is the code:

package fempack;

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.FlowLayout;
import java.awt.Point;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

import java.lang.Math;



public class MainFem extends JPanel {



final DrawPoints Npoints = new DrawPoints();
final DrawLines Nline = new DrawLines();


private static final long serialVersionUID = 1L;
private MouseHandler mouseHandler = new MouseHandler();
private Point p1 = new Point(100, 100);
public int Xpoint[][] = new int[500][30];
public int Ypoint[][] = new int[500][30];
private double Xmpoint[][] = new double[500][1000]; // [i γραμμή][συντεταγμένη Χ]
private double Ympoint[][] = new double[500][1000]; 

private double Vec[][][] = new double[500][2][500]; // [i γραμμή][0,1][0α 1β]


private double dist[] = new double[10000];
private boolean drawing;
private int c1;
private int c2;

public MainFem() {

    this.addMouseListener(mouseHandler);
    this.addMouseMotionListener(mouseHandler);

}


// --------------    Draw by clicking -----------------------

private class MouseHandler extends MouseAdapter {

    @Override
    public void mousePressed(MouseEvent e) {
        if(SwingUtilities.isRightMouseButton(e)){
            drawing=false;
            c2++;

        }
        if(SwingUtilities.isLeftMouseButton(e)){

        p1 = e.getPoint();
        Xpoint[c1][c2] = p1.x;
        Ypoint[c1][c2] = p1.y;




        if (c1 > 3) {

                 for (int j = 0; j<c2+1; j++){
                     for (int i = 0; i<c1; i++){


                if ((Math.abs(Xpoint[i][j]-Xpoint[c1][c2]) < 10) && (Math.abs(Ypoint[i][j]-Ypoint[c1][c2]) < 10)) {


                    Xpoint[c1][c2] = Xpoint[i][j];
                    Ypoint[c1][c2] = Ypoint[i][j];
                    System.out.println(Xpoint[i][j]);

                 }
                }
            }
            }

        if (drawing == true){
            Nline.addLine(Xpoint[c1][c2], Ypoint[c1][c2], Xpoint[c1-1][c2], Ypoint[c1-1][c2]);
       }



        c1++;
        drawing = true;

        }
    }


}


// ---------------- Create Mesh Points --------------------------

public void createmesh() {
int mdi = 0;


 for (int j = 0; j<=c2; j++){
    for (int i = 0; i<c1-1; i++){

        // Υπολογισμός a και b συνιστωσών της εξίσωσης της γραμμής


        Vec[i][0][mdi] = (Ypoint[i+1][j] - Ypoint[i][j])/(Xpoint[i+1][j] - Xpoint[i][j]);
        Vec[i][1][mdi] = Ypoint[i][j] - Xpoint[i][j]*Vec[i][1][mdi];


        // Υπολογισμός μέτρου διανύσματος

             dist[mdi] = Math.sqrt(Math.pow(Xpoint[i][j] - Xpoint[i+1][j], 2) + Math.pow(Ypoint[i][j] - Ypoint[i+1][j], 2)  );



        // Υπολογισμός ενδιάμεσον σημείων 

            int nkom = 3;
        double xa =  Xpoint[i][j];
        double ya = Ypoint[i][j];

        for (int ii = 0; ii <nkom; ii++) {
            double a = Vec[i][0][mdi];
            double b = Vec[i][1][mdi];

            Xmpoint[i][ii] = (-((2*a)*(b - ya) - 2*xa) + Math.sqrt(Math.abs(Math.pow(((2*a)*(b - ya) - 2*xa), 2) - 4*(1 + a*a)*(xa*xa + Math.pow((b - ya),2) -  Math.pow(dist[mdi]/nkom,2)))))/(2 + 2*a*a);


        Ympoint[i][ii] = a*Xmpoint[i][ii] + b;


        double xm11 = Xmpoint[i][ii];
        double ym11 = Ympoint[i][ii];
        int xm1 = (int) xm11;
        int ym1 = (int) ym11;

        Npoints.addPoint(xm1, ym1);


        System.out.println("i:" + ym11  + "...ii:" + ym1 );

        xa = Xmpoint[i][ii];
        ya = Ympoint[i][ii];
        }





        mdi++;


     }
    }
}



//------------------------- Display ---------------------------





private void display() {
    JFrame f = new JFrame("LinePanel");
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    f.setPreferredSize(new Dimension(500, 600));

    f.setLocationRelativeTo(null);




    f.add(Npoints);
    f.add(Nline);





    JPanel buttonsPanel = new JPanel();



    //-----------------Complete---------------

    JButton dcomp = new JButton("Complete");
    buttonsPanel.add(dcomp);


    dcomp.addActionListener(new ActionListener() {

        @Override
        public  void actionPerformed(ActionEvent e) {

            createmesh();

        }
    });


    //------------------Clean-------------------

    JButton clearButton = new JButton("Clear");
    buttonsPanel.setBorder(BorderFactory.createLineBorder(Color.black));
    buttonsPanel.setPreferredSize(new Dimension(500, 100));
    f.add(buttonsPanel, BorderLayout.SOUTH);
    buttonsPanel.add(clearButton);


    clearButton.addActionListener(new ActionListener() {

        @Override
        public void actionPerformed(ActionEvent e) {
            Nline.clearLines();
        }
    });
    f.pack();
    f.setVisible(true);
    f.add(this);

}




//---------------------------------------------------------

public static void main(String[] args) {



    EventQueue.invokeLater(new Runnable() {

        @Override
        public void run() {

            new MainFem().display();


        }
    });
}
}

Class to draw lines:

package fempack;


   import java.awt.Graphics;
   import java.util.LinkedList;

   import javax.swing.JPanel;


   public class DrawLines extends JPanel {


       /**
        * 
        */
       private static final long serialVersionUID = 1L;

 public DrawLines() {

 }

private static class Line{
    final int x1; 
    final int y1;
    final int x2;
    final int y2;   


    public Line(int x1, int y1, int x2, int y2) {
        this.x1 = x1;
        this.y1 = y1;
        this.x2 = x2;
        this.y2 = y2;

    }



}

private final LinkedList<Line> lines = new LinkedList<Line>();



public void addLine(int x1, int x2, int x3, int x4) {
    lines.add(new Line(x1,x2,x3,x4));   

    repaint();
}



public void clearLines() {
    lines.clear();
    repaint();

}


@Override
protected void paintComponent(Graphics g) {

    super.paintComponent(g);

    for (Line line : lines) {
        // System.out.println(line);

     g.drawLine(line.x1, line.y1, line.x2, line.y2);
    }



   }

   }

And class to draw Circles:

       package fempack;

   import java.awt.Graphics;

   import javax.swing.JPanel;

   import java.util.LinkedList;


   public class DrawPoints extends JPanel {


private static final long serialVersionUID = 1L;

 public DrawPoints() {

 }




private static class Point {
     final int x;
     final int y;


     public Point(int x, int y) {
         this.x = x;
         this.y = y;
     }
}

private final LinkedList<Point> points = new LinkedList<Point>();


public void addPoint(int x, int y) {
    points.add(new Point(x,y));   
   // System.out.println(x);
    repaint();
}




@Override
protected void paintComponent(Graphics g) {

    super.paintComponent(g);

    for (Point point : points) {
    //  System.out.println(point);

     g.drawOval(point.x, point.y, 5, 5);

    }
   }

   }