Question

Write a generic class Pair which has two type parameters \(-F\) and \(S,\) each representing the type of the first and second element of the pair, respectively. Add get and set methods for the first and second elements of the pair. [Hint: The class header should be public class Pair \( < \mathrm{F}, \mathrm{S} > .\)

Short answer

Create a generic class `Pair` with constructor, getters, and setters.

Step-by-step solution

Define the Class Header

Start by defining the class header for the generic class `Pair`. The header should indicate that it accepts two type parameters, `F` and `S`, representing the types of the first and second elements respectively. It should look like this: ```java public class Pair { ``` This header initiates the definition of a class that can be used with any types for its parameters.

Declare Instance Variables

Inside the `Pair` class, declare two instance variables that will hold the first and second elements of the pair. These should be of types `F` and `S` to make the class generic: ```java private F first; private S second; ```

Create a Constructor

Provide a constructor for the `Pair` class that initializes the first and second elements. This constructor should take parameters of types `F` and `S` and assign them to the instance variables: ```java public Pair(F first, S second) { this.first = first; this.second = second; } ```

Implement Getter Methods

Add getter methods for both the first and second elements. These methods will return the corresponding instance variables: ```java public F getFirst() { return first; } public S getSecond() { return second; } ```

Implement Setter Methods

Add setter methods to allow changing the values of the first and second elements. These methods should take a parameter of the respective type and update the corresponding instance variable: ```java public void setFirst(F first) { this.first = first; } public void setSecond(S second) { this.second = second; } ```

Close the Class Definition

Finally, ensure that the class definition is closed properly with a closing curly brace: ```java } ```

Key concepts

Object-Oriented Programming

In programming, **object-oriented programming (OOP)** is a style of coding where developers build models around "objects." These objects represent real-world entities with both data and methods that act on the data.
In Java, everything revolves around classes and objects.

• Classes are blueprints for objects. They define what data an object can hold and what operations can be performed on that data through methods.
• Objects are specific instances of classes. When you create an object, you're using the blueprint provided by the class to produce something tangible you can work with.

The exercise given is a great example of OOP in action. By creating a `Pair` class, you define a template for pairs of elements in your program.
The objects of this class will store two values and provide methods (getters and setters) to access and modify them.

Generic Classes

A **generic class** in Java allows you to create classes that work with any data type. This means instead of coding a class for each data type, you write one flexible class that can be reused.
Generics introduce a way to create a single class or method that can operate on different data types. They help ensure type safety without sacrificing reusability.

• In our provided solution, the `Pair` class is generic as it defines two type parameters, `F` and `S`.
• These parameters act as placeholders for data types when objects are created from this class.

For instance, by replacing `F` and `S` with `Integer` and `String`, you can create a `Pair` of those types. This flexibility eliminates the need for multiple, similar classes, and helps prevent errors by catching type mismatches at compile time rather than at runtime.

Type Parameters

**Type parameters** are the cornerstones of Java generics. They enable programmers to pass a datatype as a parameter to classes, interfaces, and methods. This allows a class to handle data in a type-safe manner while preserving its reusability.
In our `Pair` class example:

• The type parameters, denoted as ``, allow the class to work with any types for the "first" and "second" elements.
• These type parameters can be substituted with any non-primitive type when creating an instance of the `Pair` class.

For example, when instantiating a `Pair` object like `new Pair("Apple", 123);`:

• `F` becomes `String`, representing the first element's type.
• `S` becomes `Integer`, for the second element's type.

By using type parameters, Java developers can write more flexible and functional classes that can operate with a multitude of types without losing type specificity.

Getters and Setters

In Java, **getters and setters** are special methods used to access and update the value of instance variables. They are a fundamental concept in encapsulation, one of the four principles of OOP.

• **Getters**, also known as accessors, provide the value of a private variable to the outside world.
• **Setters**, also known as mutators, allow modification of a private variable's value.

In the `Pair` class solution, the getter methods `getFirst()` and `getSecond()` return the values of the first and second elements of the pair, respectively.
The setter methods `setFirst(F first)` and `setSecond(S second)` allow these values to be changed.
Using getters and setters has several benefits:

• They make the class more maintainable by controlling access to the fields.
• They allow internal data to be changed without affecting the rest of the program.
• They enhance security and encapsulation by restricting direct access to an object's fields.

By creating these methods, developers ensure that their object's state can be managed effectively and safely from outside the class.