java.util.Properties

java.util.Properties is a  subclass of Hashtable<Object, Object>.This is used to maintain lists of values in which both keys and values are strings.Ideal for configuration data like settings, messages, or environment variables.Often used to read/write .properties files in Java apps.

Commonly used Constructors and Methods

Simple Program

import java.util.Properties;

public class SimplePropertiesExample {
    public static void main(String[] args) {
        Properties config = new Properties();

        config.setProperty("username", "admin");
        config.setProperty("password", "1234");
        config.setProperty("timeout", "30");

        System.out.println("Username: " + config.getProperty("username"));
        System.out.println("Timeout: " + config.getProperty("timeout"));
    }
}

Output

Username: admin
Timeout: 30Code language: HTTP (http)

Problem Statement:

LotusJavaPrince and Mahesh are building a banking admin panel that uses an external .properties file for configuration settings like database URL, username, password, and application mode (dev/prod). They want a Java program that loads and displays these settings from the properties file.

config.properties File:

db.url=jdbc:mysql://localhost:3306/bank
db.user=lotusjavaprince
db.password=securepass
app.mode=productionCode language: JavaScript (javascript)

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

public class ConfigLoader {
    public static void main(String[] args) {
        Properties config = new Properties();

        try {
            // Load from file
            FileReader reader = new FileReader("config.properties");
            config.load(reader);

            System.out.println("Database URL: " + config.getProperty("db.url"));
            System.out.println("User: " + config.getProperty("db.user"));
            System.out.println("App Mode: " + config.getProperty("app.mode"));
        } catch (IOException e) {
            System.out.println("Error loading config file: " + e.getMessage());
        }
    }
}

Output

Database URL: jdbc:mysql://localhost:3306/bank
User: lotusjavaprince
App Mode: productionCode language: JavaScript (javascript)

The java.util.Properties class is a powerful and lightweight tool for managing configuration data in Java applications. Whether used in-memory or with external files, it offers a simple key-value based solution that’s ideal for settings, localization, and environment configuration.