如何在"readProperties文件“中添加额外的属性？

# 示例readProperties文件
database.url=jdbc:mysql://localhost:3306/mydatabase
database.username=admin
database.password=123456

import java.io.FileInputStream;
import java.io.IOException;
import java.util.Properties;

public class ReadPropertiesExample {
    public static void main(String[] args) {
        Properties properties = new Properties();
        try {
            properties.load(new FileInputStream("readProperties文件"));

            String databaseUrl = properties.getProperty("database.url");
            String databaseUsername = properties.getProperty("database.username");
            String databasePassword = properties.getProperty("database.password");

            System.out.println("Database URL: " + databaseUrl);
            System.out.println("Database Username: " + databaseUsername);
            System.out.println("Database Password: " + databasePassword);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}