Java swing why when i draw a lot of strings in a panel that is inside a JScrollpane they overlap?

Question

I'm new in java swing.
I want to do draw a lot of rectangles that inside have a number. Because of this i put the panel that extends JPanel in a JScrollpane.
I noticed that if i have few rectangles it works pretty well but if i draw a lot of rectangles the strings overlap each other (see the image). Can someone help me to fix it?.
Thank you.

Code:

import java.util.*; 
import java.io.*;
import javax.swing.*;
import java.awt.*;
class drawing extends JFrame
{
    private myPanel gg=new myPanel();
    drawing(){
        setLayout(new BorderLayout());
        add(new JLabel("HELLO"), "North");
        add(new JScrollPane(gg), "Center");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setExtendedState(MAXIMIZED_BOTH);
    }
    public static void main(String argv[]){
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                drawing prova=new drawing();
                prova.setVisible(true);
            }
        });
        return;
    }
}
class myPanel extends JPanel
{
    private void drawCenteredStringInRect(Graphics2D g2d, String text, int base, int height, int xRect, int yRect){
        FontMetrics fm = g2d.getFontMetrics();
        int x=xRect+((base-fm.stringWidth(text))/2);
        int y=yRect+(((height-fm.getHeight())/2)+ fm.getAscent());
        System.out.print(x+" "+y+"\n");
        g2d.drawString(text, x, y); //(string, x, y)
        return;
    }
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d=(Graphics2D)g;
        int base=80, height=20, xRect=5, yRect=5;
        String num="2147483648";
        //x1 y1, x2 y2
        for(int i=0;i<=50000;++i){
            if(i%10==0){
                xRect=5;
                yRect+=height+10;
            }
            xRect+=base+5;
            g2d.drawRect(xRect, yRect, base, height); //(x, y, base, height)
            drawCenteredStringInRect(g2d, Integer.toString(i), base, height, xRect, yRect);        
        }
        return;
    }
    public Dimension getPreferredSize() {
            return new Dimension(500, 10000000);
    }
}

EDIT_1: i don't understand why there are so many strings. There should be one per rectangle. Like so:

Answer 1

A JTable will handle & display 50 million numbers quickly and easily (with correct rendering). Note that the JLabel used as the cell renderer is a single component used to paint every table cell.

import java.awt.*;
import javax.swing.*;
import javax.swing.table.*;
import javax.swing.border.*;

public class FiftyMillionNumbersInTable {

    private JComponent ui = null;

    FiftyMillionNumbersInTable() {
        initUI();
    }

    public final void initUI() {
        if (ui!=null) return;

        ui = new JPanel(new BorderLayout(4,4));
        ui.setBorder(new EmptyBorder(4,4,4,4));
        int maxNum = 5000000;
        int colNum = 10;
        Integer[] cols = {1,2,3,4,5,6,7,8,9,10};
        Integer[][] numbers = new Integer[maxNum/colNum][colNum];
        for (int ii=0; ii<maxNum; ii++) {
            numbers[ii/colNum][(ii%colNum)] = ii;
        }
        JTable table = new JTable(numbers, cols);
        table.setDefaultRenderer(Object.class, new CenterCellRenderer());
        ui.add(new JScrollPane(table));
    }

    class CenterCellRenderer extends DefaultTableCellRenderer {

        @Override
        public Component getTableCellRendererComponent(
                JTable table, Object value, 
                boolean isSelected, boolean hasFocus, 
                int row, int column) {
            Component c = super.getTableCellRendererComponent(table, value, 
                    isSelected, hasFocus, row, column);
            JLabel l = (JLabel)c;
            l.setHorizontalAlignment(SwingConstants.CENTER);
            return l;
        }
    }

    public JComponent getUI() {
        return ui;
    }

    public static void main(String[] args) {
        Runnable r = () -> {
            FiftyMillionNumbersInTable o = new FiftyMillionNumbersInTable();

            JFrame f = new JFrame(o.getClass().getSimpleName());
            f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
            f.setLocationByPlatform(true);

            f.setContentPane(o.getUI());
            f.pack();
            f.setMinimumSize(f.getSize());

            f.setVisible(true);
        };
        SwingUtilities.invokeLater(r);
    }
}