通过JDBC相关的API实现学生成绩的添加、修改、查询、统计等功能，采用图形界面，数据库采用MySQL，写出完整java代码

以下是一个简单的示例代码，实现学生成绩的添加、修改、查询、统计等功能，采用图形界面，数据库采用MySQL：

import java.awt.BorderLayout;
import java.awt.EventQueue;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import javax.swing.JLabel;
import javax.swing.JTextField;
import javax.swing.JButton;
import javax.swing.JTable;
import javax.swing.table.DefaultTableModel;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class StudentGradeGUI extends JFrame {

    private JPanel contentPane;
    private JTextField textFieldName;
    private JTextField textFieldScore;
    private JTable table;
    private DefaultTableModel model;
    
    private Connection conn;
    private PreparedStatement stmt;
    private ResultSet rs;

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    StudentGradeGUI frame = new StudentGradeGUI();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the frame.
     */
    public StudentGradeGUI() {
        // connect to database
        try {
            Class.forName("com.mysql.jdbc.Driver");
            String url = "jdbc:mysql://localhost:3306/student";
            conn = DriverManager.getConnection(url, "root", "password");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 450, 300);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        setContentPane(contentPane);
        contentPane.setLayout(null);

        JLabel lblName = new JLabel("Name");
        lblName.setBounds(10, 11, 46, 14);
        contentPane.add(lblName);

        textFieldName = new JTextField();
        textFieldName.setBounds(66, 8, 86, 20);
        contentPane.add(textFieldName);
        textFieldName.setColumns(10);

        JLabel lblScore = new JLabel("Score");
        lblScore.setBounds(10, 36, 46, 14);
        contentPane.add(lblScore);

        textFieldScore = new JTextField();
        textFieldScore.setBounds(66, 33, 86, 20);
        contentPane.add(textFieldScore);
        textFieldScore.setColumns(10);

        JButton btnAdd = new JButton("Add");
        btnAdd.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                addStudentGrade();
            }
        });
        btnAdd.setBounds(10, 61, 89, 23);
        contentPane.add(btnAdd);

        JButton btnUpdate = new JButton("Update");
        btnUpdate.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                updateStudentGrade();
            }
        });
        btnUpdate.setBounds(109, 61, 89, 23);
        contentPane.add(btnUpdate);

        JButton btnSearch = new JButton("Search");
        btnSearch.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                searchStudentGrade();
            }
        });
        btnSearch.setBounds(208, 61, 89, 23);
        contentPane.add(btnSearch);

        JButton btnStat = new JButton("Stat");
        btnStat.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                statStudentGrade();
            }
        });
        btnStat.setBounds(307, 61, 89, 23);
        contentPane.add(btnStat);

        table = new JTable();
        model = new DefaultTableModel(new Object[][] {}, new String[] { "Name", "Score" });
        table.setModel(model);
        table.setBounds(10, 95, 386, 156);
        contentPane.add(table);
    }

    // add student grade to database
    private void addStudentGrade() {
        try {
            String name = textFieldName.getText();
            int score = Integer.parseInt(textFieldScore.getText());
            String sql = "INSERT INTO grade (name, score) VALUES (?, ?)";
            stmt = conn.prepareStatement(sql);
            stmt.setString(1, name);
            stmt.setInt(2, score);
            stmt.executeUpdate();
            model.addRow(new Object[] { name, score });
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    // update student grade in database
    private void updateStudentGrade() {
        try {
            String name = textFieldName.getText();
            int score = Integer.parseInt(textFieldScore.getText());
            String sql = "UPDATE grade SET score = ? WHERE name = ?";
            stmt = conn.prepareStatement(sql);
            stmt.setInt(1, score);
            stmt.setString(2, name);
            int rowsAffected = stmt.executeUpdate();
            if (rowsAffected == 0) {
                System.out.println("No rows affected.");
            } else {
                System.out.println(rowsAffected + " rows affected.");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    // search student grade from database
    private void searchStudentGrade() {
        try {
            String name = textFieldName.getText();
            String sql = "SELECT * FROM grade WHERE name LIKE ?";
            stmt = conn.prepareStatement(sql);
            stmt.setString(1, "%" + name + "%");
            rs = stmt.executeQuery();
            model.setRowCount(0);
            while (rs.next()) {
                String resultName = rs.getString("name");
                int resultScore = rs.getInt("score");
                model.addRow(new Object[] { resultName, resultScore });
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    // stat student grade from database
    private void statStudentGrade() {
        try {
            String sql = "SELECT AVG(score) as avg_score, COUNT(*) as count FROM grade";
            stmt = conn.prepareStatement(sql);
            rs = stmt.executeQuery();
            model.setRowCount(0);
            while (rs.next()) {
                double avgScore = rs.getDouble("avg_score");
                int count = rs.getInt("count");
                model.addRow(new Object[] { "Average Score", avgScore });
                model.addRow(new Object[] { "Number of Students", count });
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

注意：这只是一个简单的示例代码，实际使用时需要根据实际情况进行修改和完善。例如，需要对用户输入进行验证和处理，需要处理数据库连接和关闭等异常情况。