If a table column can have a null value or not : Column « Database « Java Tutorial

1. Java Tutorial
2. Database
3. Column

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.Statement;

public class Main {
  private static final String DRIVER = "com.mysql.jdbc.Driver";

  private static final String URL = "jdbc:mysql://localhost/testdb";

  private static final String USERNAME = "root";

  private static final String PASSWORD = "";

  public static void main(String[] args) throws Exception {
    Class.forName(DRIVER);
    Connection connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);

    Statement statement = connection.createStatement();
    ResultSet resultSet = statement.executeQuery("SELECT id, username FROM users");
    ResultSetMetaData metadata = resultSet.getMetaData();
    int nullability = metadata.isNullable(1);

    if (nullability == ResultSetMetaData.columnNullable) {
      System.out.println("Columns ID can have a null value");
    } else if (nullability == ResultSetMetaData.columnNoNulls) {
      System.out.println("Columns ID does not allowed to have a null value");
    } else if (nullability == ResultSetMetaData.columnNullableUnknown) {
      System.out.println("Nullability unknown");
    }
  }
}