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Properties is a legacy class and it extends HashTable legacy class.

• Basically, Properties class is used to access system's properties like - version of Operation System, JVM, Java compiler, environment variables etc.
• Properties class can also be used to add new properties in the form of key-value pairs, where key and value are String objects. And for a given key, we can find its associated value.

Important point about Properties class

While creating an object of Properties, we cannot specify the type of objects Properties class will hold, as it can only hold String type of objects, for example -

Properties prop = new Properties();

Note :

Just like its parent class(HashTable), Properties class also stores the data by using the hash code of its keys and hence the order in which its elements are stored and displayed is not guaranteed.

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Some legacy methods in Properties class.

As Properties is a subclass of HashTable legacy class, so some of its methods are inherited by HashTable class. While some of its own specific methods make it a specialized in setting new properties or accessing existing non-system or system properties.

Methods	Description
int size()	Returns the total number of elements in Stack.
boolean empty()	Returns true if Stack is empty, else false.
String getProperty(String key)	Pushes the element on the top of Stack.
Object setProperty(String key, String value)	Sets a new property in System.
void list(PrintStream out)	Sends the list of properties to the output stream.

Let's understand Properties class by an example

import java.util.*;

class Properties1
{
public static void main(String... ar)
{
Properties prop= new Properties();
 
prop.setProperty("Football", "Pele");
prop.setProperty("Golf", "Tiger Woods");
prop.setProperty("Formula 1", "Michael Schumacher");
prop.setProperty("Basketball", "Michael Jordan");
prop.setProperty("Boxing", "Mohammad Ali");

System.out.println("Size of properties = "+ prop.size());

System.out.println("Value associated with Key, Golf = "+ prop.getProperty("Golf"));

//using list() method to send the list of properties on the output stream, "System.out"
prop.list(System.out);

}

}

Output is :

Size of properties = 5
Value associated with Key, Golf = Tiger Woods
-- listing properties --
Boxing=Mohammad Ali
Football=Pele
Basketball=Michael Jordan
Golf=Tiger Woods
Formula 1=Michael Schumacher

Program Analysis

• We have created a new object of Properties class to create and store new properties.
• Method setProperty() is used to add new Properties in the form of key-value pair, where key and value are String objects.
• Method size() is called to show the total number of properties refrenced by reference variable, prop.
• Method getProperty() has returned the value associated with the key "Golf", i.e.."Tiger Woods".
• Method list() has sent the list of properties referenced by prop, to the output stream i.e. "System.out", which writes the list of properties to the console.

Note :

To display all the properties set in our system like version of OS, JVM, environment variables etc, we should call properties() method of System class, which also returns an object of Properties class -:

 Properties prop= System.getProperties();

and using this prop reference variable of Properties type, we can display all the properties set in our system(it can be a long list).

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