How do you use generics to reuse software?

1 What are generics?

Generics are a way of defining classes, methods, or interfaces that can operate on different types of data, without specifying the exact type at the time of writing. For example, you can create a generic class that represents a list of items, and then use it to store and manipulate lists of integers, strings, or any other type. The generic class can have methods that apply to any type of item, such as adding, removing, or sorting. The type of the items is determined by the type parameter, which is a placeholder that is replaced by the actual type when the generic class is instantiated.

2 Why use generics?

Generics have several benefits for software reuse. First, they reduce code duplication, since you don't have to write separate classes or methods for each type of data. This makes your code more concise, consistent, and maintainable. Second, they increase type safety, since they prevent errors such as assigning a string to an integer variable, or passing a wrong type of argument to a method. Generics enforce compile-time checks that ensure that the types are compatible and consistent. Third, they enhance readability, since they express the intent and functionality of the code more clearly and explicitly. Generics make your code more self-documenting and easier to understand.

3 How to use generics?

To use generics, you need to follow some basic syntax and rules. First, you need to declare the type parameter using angle brackets (< and >) after the name of the class, method, or interface. For example, to define a generic class named Box that can hold any type of object, you write:

class Box<T> {
  private T item;
  public void setItem(T item) {
    this.item = item;
  }
  public T getItem() {
    return item;
  }
}        

The type parameter T is a placeholder that can be replaced by any type when the class is used. For example, to create a box that holds an integer, you write:

Box<Integer> intBox = new Box<>();
intBox.setItem(42);        

To create a box that holds a string, you write:

Box<String> strBox = new Box<>();
strBox.setItem("Hello");        

Second, you need to respect the bounds and constraints of the type parameter. Bounds are restrictions that limit the types that can be used as the type parameter. For example, you can specify that the type parameter must be a subclass of a certain class, or implement a certain interface. Constraints are rules that define how the type parameter can be used in the code. For example, you can specify that the type parameter must have a default constructor, or support certain operations.

4 How to design generics?

Designing generics requires careful planning and consideration of the trade-offs and implications of using generics. Therefore, here are some guidelines and best practices to help you design generics: when writing code that works with different types of data, use generics when the type of data is not known or relevant. Select meaningful and consistent names for the type parameters, such as T, E, K, V, or N, or opt for descriptive names that indicate the role or purpose of the type parameter. Avoid raw types, as they are not type-safe and can cause runtime errors. Prefer generic methods over generic classes when possible; they are more flexible and reusable. Use bounded type parameters to restrict the types used as the type parameter and access methods and properties of the bound type. Additionally, wildcards can be employed to increase flexibility and compatibility of generic types, especially when dealing with collections or arrays of generic types. Upper bounded wildcards use the extends keyword to indicate that the unknown type is a subclass of a certain type while lower bounded wildcards use the super keyword to indicate that the unknown type is a superclass of a certain type.

5 What are some examples of generics?

Generics are widely used in object oriented programming, especially in the Java programming language, which introduced generics in version 5.0. For instance, the Java Collections Framework offers generic classes and interfaces for storing and manipulating collections of objects, such as lists, sets, maps, queues, and stacks. The Java Stream API provides a way of processing sequences of data using functional programming techniques, such as map, filter, reduce, and collect. Additionally, the Java Generics and Collections book is a comprehensive guide to using generics and collections in Java written by Maurice Naftalin and Philip Wadler. It covers the syntax, semantics, and design of generics, as well as the features and benefits of the collections framework with examples and exercises to help you master generics and collections.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?