Properties Class in Java

The Properties class in Java is a specialized collection used to manage application settings and configuration data. It extends the Hashtable class and provides convenient methods for reading, storing, and updating property values from external files.

• Provides built-in methods such as load() and store() for handling configuration files.
• Inherits synchronization and key-value storage features from Hashtable.
• Widely used for managing environment-specific settings without modifying source code.

Constructors of Properties 

1. Properties(): This creates a Properties object that has no default values. 

Properties p = new Properties();

2. Properties(Properties propDefault): The second creates an object that uses propDefault for its default value. 

Properties p = new Properties(Properties propDefault);

Example: Reading Data from a Properties File

Create a properties file named db.properties and store key-value pairs in it.

username = coder
password = geeksforgeeks

The following program demonstrates how to read and retrieve values from a properties file using the Properties class in Java.

import java.util.*;
import java.io.*;

public class GFG {
    public static void main(String[] args) throws Exception {

        // Create a reader object for the properties file
        FileReader reader = new FileReader("db.properties");

        // Create Properties object
        Properties p = new Properties();

        // Load properties from file
        p.load(reader);

        // Access property values
        System.out.println(p.getProperty("username"));
        System.out.println(p.getProperty("password"));
    }
}

Output

Example: Getting All System Properties

The following program demonstrates how to retrieve and display all system properties using the System.getProperties() method.

import java.util.*;
import java.io.*;

public class GFG {
    public static void main(String[] args) throws Exception
    {
        // get all the system properties
        Properties p = System.getProperties();

        // stores set of properties information
        Set set = p.entrySet();

        // iterate over the set
        Iterator itr = set.iterator();
        while (itr.hasNext()) {

            // print each property
            Map.Entry entry = (Map.Entry)itr.next();
            System.out.println(entry.getKey() + " = "
                               + entry.getValue());
        }
    }
}

Output

Example: Creating a Properties File

The following program demonstrates how to create a properties file and store key-value pairs using the Properties class in Java.

import java.util.*;
import java.io.*;

public class GFG {
    public static void main(String[] args) throws Exception
    {
        // create an instance of Properties
        Properties p = new Properties();

        // add properties to it
        p.setProperty("name", "Ganesh Chowdhary Sadanala");
        p.setProperty("email",
                      "[email protected]");

        // store the properties to a file
        p.store(new FileWriter("info.properties"),
                "GeeksforGeeks Properties Example");
    }
}

Output

Advantages

• Stores configuration data in a simple key=value format.
• Makes application settings easy to read and modify without changing source code.
• Supports loading and storing data from files and streams.
• Provides built-in methods such as load(), store(), getProperty(), and setProperty().
• Commonly used for database, application, and system configuration settings.

Limitations

• Supports only String keys and String values.
• Does not support complex or hierarchical data structures.
• Changes made to a properties file require reloading to reflect updates in the application.

Methods of Properties

Methods declared in class java.util.Hashtable

Methods declared in interface java.util.Map