Properties Class in Java

The Properties class represents a persistent set of properties. The Properties can be saved to a stream or loaded from a stream. It belongs to java.util package. Properties define the following instance variable. This variable holds a default property list associated with a Properties object. 

Properties defaults: This variable holds a default property list associated with a Properties object.
 

Features of Properties class:

• Properties is a subclass of Hashtable.
• It is used to maintain a list of values in which the key is a string and the value is also a string i.e; it can be used to store and retrieve string type data from the properties file.
• Properties class can specify other properties list as it's the default. If a particular key property is not present in the original Properties list, the default properties will be searched.
• Properties object does not require external synchronization and Multiple threads can share a single Properties object.
• Also, it can be used to retrieve the properties of the system.

Advantage of a Properties file

In the event that any data is changed from the properties record, you don't have to recompile the java class. It is utilized to store data that is to be changed habitually.

Note: The Properties class does not inherit the concept of a load factor from its superclass, Hashtable.

Declaration

public class Properties extends Hashtable<Object,​Object>

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 1: The below program shows how to use Properties class to get information from the properties file. 

Let us create a properties file and name it as db.properties.

db.properties

username = coder
password = geeksforgeeks

Code

// Java program to demonstrate Properties class to get
// information from the properties file

import java.util.*;
import java.io.*;
public class GFG {
    public static void main(String[] args) throws Exception
    {
        // create a reader object on the properties file
        FileReader reader = new FileReader("db.properties");

        // create properties object
        Properties p = new Properties();

        // Add a wrapper around reader object
        p.load(reader);

        // access properties data
        System.out.println(p.getProperty("username"));
        System.out.println(p.getProperty("password"));
    }
}

Output

Example 2: The below program shows how to use the Properties class to get all the system properties. Using System.getProperties() method, we can get all the properties of the system.

// Java program to demonstrate Properties class to get all
// the system properties

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 3: The below program shows how to use the Properties class to create a properties file.

// Java program to demonstrate Properties class to create
// the properties file

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

Methods of Properties

Methods declared in class java.util.Hashtable

Methods declared in interface java.util.Map