Question

Write a generic class Pair which has two type parameters - F and S cach 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 \(\langle\mathrm{F}, \mathrm{S}>.]\)

Short answer

Start by defining a generic class 'Pair' with two type parameters 'F' and 'S'. Then add private member variables representing the pair elements. Provide getter and setter methods for both elements, and ensure all methods and variables are within the class scope.

Step-by-step solution

Define the Pair Class with Type Parameters

Start by defining a public class named Pair with two type parameters, F and S. This is accomplished by using angle brackets after the class name, and declaring F and S within them. The class header should look like this: public class Pair { ... }.

Add Member Variables

Inside the Pair class, declare two private member variables to store the elements of the pair. Name these variables according to the type parameters, such as 'first' for F and 'second' for S. Initialize them within the class, but outside any methods: private F first; private S second;

Create Getter and Setter Methods for First Element

Provide public methods to access and modify the first element of the pair. The getter for the first element should be named getFirst and it will return the type parameter F. The setter should be called setFirst, take a parameter of type F, and set the first member variable: public F getFirst() { return first; } public void setFirst(F first) { this.first = first; }

Create Getter and Setter Methods for Second Element

Similarly, write public methods getSecond and setSecond for the second element of the pair. These methods will handle the second type parameter S: public S getSecond() { return second; } public void setSecond(S second) { this.second = second; }

Complete the Pair Class

After declaring the member variables and writing the getter and setter methods for both first and second elements, ensure that all code is properly enclosed in the class definition. The final class definition should compile without any errors and allow creating objects of the Pair class with two generic types.

Key concepts

Type Parameters

One of the key concepts in Java programming is the use of type parameters, which allow for the creation of classes and methods that can operate on different types while maintaining strict type safety. In the context of our exercise, the Pair class utilizes type parameters F and S to represent the first and second elements of a pair, respectively.

When defining a generic class, type parameters are specified within angle brackets (<>) following the class name. These parameters act as placeholders for the types that will be specified when an instance of the class is created. In practice, this means you can use the Pair class to hold any two objects, whether it be Pair or Pair, effectively making the class a flexible container.

In the solution, you see public class Pair which demonstrates the syntax for class definition with type parameters. This allows the class to be instantiated with any types for its two fields, providing a high degree of reusability and type safety.

Getter and Setter Methods

In Java, getter and setter methods are a staple of encapsulation - a principle of object-oriented programming that restricts direct access to the object's internal state. Instead of directly interacting with the fields of a class, other objects must use these methods to retrieve (get) or modify (set) the class's properties.

In our generic Pair class, getters and setters play a crucial role. They provide a controlled access to the private variables first and second, corresponding to the first and second elements of the pair. The methods getFirst and getSecond serve to return the current values of these elements, while setFirst and setSecond allow the caller to change those values.

For instance, setFirst(F first) assigns the input to the field first, encapsulating the logic of how the input is stored. Likewise, getSecond() will simply return the value of second, abstracting away the internal representation of that value.

Class Definition in Java

A class definition in Java is a blueprint from which individual objects are created. The class defines properties, referred to as member variables, and behaviors, known as methods. A well-defined class encapsulates all the functionality that the objects created from it can exhibit.

The solution provided for the exercise outlines the fundamentals of a class definition with the example of the Pair class. It starts with the visibility keyword public, followed by the keyword class, and then the class name. Within the curly braces { ... }, you define the internal structure of the class: its variables and methods.

In the Pair class, there are private member variables first and second, reflecting the idea that these should not be accessible directly. The getter and setter methods defined in the subsequent steps provide controlled access to these variables. This class structure is a fundamental concept in Java and forms the basis of much of Java's object-oriented capabilities.