A **pair class** is a very useful programming concept. It supplies a helpful way of managing key to value association.

Pairs are especially helpful when two values are to be returned from a method. For example, there could be a method which computes the square root of a number and returns both the square root and the number itself. Hence, we want to combine a number with its square root. The combination may result in (number, square root of a number), ex., (16,4) and (25,5).

Let's look at another example of where pairs can be helpful. Imagine there is a list or an array of integers, and we want to create a pair of even numbers from that array. 

# Types of Pairs:
* **Mutable pair**: pairs of data values which can be changed. We can call getter and setter functions on this. We can call functions on this: `pair.getValue();` or `pair.setValue(1,2)`. 
  
  Here getValue returns the values stored in the pair, and SetValues sets the values of the pairs.

* **Immutable pair**: pair of data values which cannot be changed/set/amended. This means that once the data values are set in the pair,then we cannot call `pair.setValue(1,2)` ie., no changes allowed. 



# Example
Simply setting and then getting the values of Pair.


@SuppressWarnings("unchecked") // to prevent warnings.
class main{
  public static void main(String args[])
  {
    Pair<Integer> pair = new Pair<Integer>();
    pair.setValue(1,2);
    Pair <Integer> answer= new Pair <Integer> ();
    answer = pair.getValue();
    System.out.println(answer.p1 + " " + answer.p2);
  }
}
class Pair<T> 
{
  T p1, p2;
  Pair()
  {
    //default constructor
  }
  void setValue(T a, T b)
  {
    this.p1 = a;
    this.p2 = b;
  }
  Pair getValue()
  {
    return this;
  }
  
}


How to create a pair class in Java

A pair class in Java manages key-value associations, aiding in returning multiple values from methods, with mutable and immutable pair types.