I'm trying to draw square in java but it doesn't work

I'm trying to draw squares to make grid system to make snake game in java but when i run my code i can't see any thing.
I made node class that has the square info like position, and grid class that has the data of all the squares and GUI class and i tried to use drawRect method but i have no result.

import javax.swing.*;
import java.awt.*;
import java.awt.geom.Rectangle2D;
import java.util.*;
import java.util.List;
public class SnakeGame {
public static void main(String[] args){
JFrame frame = new JFrame();
frame.setSize(300,300);
frame.setLayout(null);
Grids grids  = new Grids(300);
GUI gui = new GUI(grids.nodesList,grids.nodeSize);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(gui);
frame.setVisible(true);
}
public static class Node{
public float[] position = new float[2];
public Node(float[] Position){
//this is the x position
position[0] = Position[0];
//this is the y position
position[1] = Position[1];
}
}
public static class Grids{
public int nodesNum =  6;
public float screenSize;
public float nodeSize;
public float[] startNodePos = new float[2];
public List<Node> nodesList = new ArrayList<Node>();
public Grids(float ScreenSize){
screenSize = ScreenSize;
nodeSize = screenSize / nodesNum;
//set the start node position
//x
startNodePos[0] = nodeSize /2;
//y
startNodePos[1] = nodeSize /2;
//use for loop to create nodes
for (float X = startNodePos[0] ; X <= nodeSize * 5; X += nodeSize / 2) {
for (float Y = startNodePos[1]; Y <= nodeSize * 5; Y += nodeSize / 2) {
float[] Pos = {X, Y};
Node node = new Node(Pos);
nodesList.add(node);
}
}
}
}
public static class GUI extends JPanel{
public List<Node> nodes;
public float NodeSize;
public GUI(List<Node> Nodes,float nodeSize){
nodes = Nodes;
NodeSize = nodeSize;
}
@Override
public void paintComponents(Graphics g) {
super.paintComponents(g);
for(Node node : nodes){
g.setColor(Color.BLACK);
g.drawRect((int)node.position[0],(int)node.position[1],(int)NodeSize,(int)NodeSize);
}
}
}
}

There are two primary mistakes

#First

frame.setLayout(null);

This means that you will become completely responsible for determine the location and size of all child components.

In this case, it's probably just easier to get rid of it and use the default BorderLayout

#Second

You're overriding paintComponents, not paintComponent (not the s at the end)

public void paintComponents(Graphics g) {
//...
}

Since, there are no components to be painted, it's not getting called

Simple change it to paintComponent (and make sure you call it's super properly)

@Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
for (Node node : nodes) {
g.setColor(Color.BLACK);
g.drawRect((int) node.position[0], (int) node.position[1], (int) NodeSize, (int) NodeSize);
}
}

#Observations

While running through the code, I note some ... interesting things, which might cause you issues in the long run.

1. The size of the view area is not the same as the size of the window. A window also needs to display the window decorations (title bar, borders, etc), which are inset into the window. This reduces the available viewable area. It's better to have the content provide a sizing hint and pack the window around, which brings me to...
2. The model seems to be taking into consideration view properties. You should aim to have the model and view be as agnostic as possible, meaning that the model should not be dictating display state to the view. Instead, the size of the cell's, and by extensions, the size of the panel, should be determined by the view.