Grid Layout in Java is a layout manager that arranges components in a grid of rows and columns. The grid can have a fixed number of rows and columns or can be dynamically changed at runtime.

To use Grid Layout, you first create a new instance of the GridLayout class and set the number of rows and columns in the grid using the constructor. You can then set the layout manager of a container to the grid layout using the setLayout() method. When you add components to the container, they will be automatically arranged in the grid according to their order of addition.

Here's an example of how to use Grid Layout to arrange buttons in a simple calculator application:

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

public class Calculator extends JFrame {
    public Calculator() {
        setTitle("Calculator");
        setLayout(new GridLayout(4, 4));

        add(new JButton("7"));
        add(new JButton("8"));
        add(new JButton("9"));
        add(new JButton("/"));
        add(new JButton("4"));
        add(new JButton("5"));
        add(new JButton("6"));
        add(new JButton("*"));
        add(new JButton("1"));
        add(new JButton("2"));
        add(new JButton("3"));
        add(new JButton("-"));
        add(new JButton("0"));
        add(new JButton("."));
        add(new JButton("="));
        add(new JButton("+"));

        pack();
        setVisible(true);
    }

    public static void main(String[] args) {
        new Calculator();
    }
}

This code creates a JFrame window and sets its layout to a 4 by 4 grid using the GridLayout(4, 4) constructor. It then adds JButton components to the window in the order that they should appear in the grid. Finally, it packs the window and sets it to be visible.