In Java programming language, a pair class is a simple container class that holds two objects of any type. The objects are stored as a pair, which can be accessed using the methods provided by the pair class.

The pair class is typically used in situations where a method needs to return two values, but returning them separately would not make sense. For example, if a method needs to return both the minimum and maximum values in a list, it can return a pair object containing both values.

The pair class is part of the JavaFX library, which is used for creating graphical user interfaces in Java. However, it can also be used in non-graphical applications.

The pair class has two instance variables, first and second, which hold the two objects in the pair. It provides methods to get and set the values of these instance variables. The pair class also provides methods for comparing pairs and for creating new pairs.

The pair class is a simple and convenient way to represent pairs of objects in Java. It can be used in many different situations and is a useful tool for any Java programmer to have in their toolbox.