The Fundamental Concepts And Characteristics Of Imperative And Declarative Programming

This article elaborates on the fundamental concepts and characteristics of imperative and declarative programming, compares them with code examples, and succinctly summarizes their differences in one sentence.

Basic Concepts

Declarative programming is a programming paradigm that emphasizes “what to do” rather than “how to do it.” This means that during programming, developers specify the desired outcome without providing step-by-step instructions on how to achieve this result.

Main Characteristics of Declarative Programming

1. Higher Level of Abstraction: Declarative programming, by offering high-level abstractions, allows developers to focus more on the goals of business logic or algorithms, rather than the steps of their implementation. This approach can reduce the amount of code and improve development efficiency.

2. Easier to Understand and Maintain: Since declarative code directly describes the expected result, it makes the code easier to read and understand. Other developers can quickly grasp the intent of the code rather than its implementation details, which helps improve the code’s maintainability.

3. Easier Parallel Processing: Declarative programming often uses immutable data structures, reducing dependencies and conflicts during concurrent execution, making the program easier to parallelize and optimize.

4. Better Predictability and Testability: Declarative programming usually does not involve side effects, meaning the same input always produces the same output. This characteristic makes declarative programming easier to test and debug.

Difference Between Declarative and Imperative Programming

Contrary to declarative programming is imperative programming, which emphasizes how to achieve the desired result through a series of operations. This approach focuses more on changing control flow and state.

• Imperative Programming: Typically contains a lot of control structures (such as loops and conditional statements), clearly indicating the specific steps of computation. The code usually executes in the order of the instructions.

• Declarative Programming: Focuses more on expressing logic and intent rather than controlling the process. In many cases, the specific execution order and implementation details are handled by the underlying system or framework.

For example, using Jexl expressions to filter a collection of data is a declarative method. Developers only need to specify the filtering conditions without writing specific iteration logic and condition judgment code. This reflects the main characteristics of declarative programming: simplifying code by abstraction and enhancing expressiveness, making it clearer and easier to manage.

Comparison

To deeply understand the difference between declarative and imperative programming, let’s compare them with a simple example: suppose we need to filter all even numbers from an array of numbers. This task can be implemented in both imperative and declarative programming ways.

Imperative Programming Example

In imperative programming, we explicitly specify every step of “how to do it”:

const numbers = [1, 2, 3, 4, 5, 6];
const evens = [];

for (let i = 0; i < numbers.length; i++) {
  if (numbers[i] % 2 === 0) {
    evens.push(numbers[i]);
  }
}

console.log(evens); // Output: [2, 4, 6]

In this example, we used a loop to iterate through the array, and for each element, we made a “whether it’s an even number” judgment. If so, it is added to the result array. This process detailed every step needed to achieve the goal.

Declarative Programming Example

In declarative programming, we only need to describe “what we want”:

const numbers = [1, 2, 3, 4, 5, 6];

const evens = numbers.filter(n => n % 2 === 0);

console.log(evens); // Output: [2, 4, 6]

Here, we used the filter method to declare our desired result: a new array containing only even numbers. We don’t need to worry about how to iterate through the array or manually manage intermediate states (such as temporarily storing even numbers). All these details are abstracted by the filter method; we only need to provide a function that determines whether an element should be included in the final result.

Summary

By comparing these two examples, it’s evident that imperative programming focuses on the specific steps of “how to do it,” involving explicit descriptions of control flow (such as loops and condition judgments), while declarative programming focuses on “what we want,” using high-level abstractions to directly express goals, thus simplifying code logic, making it more concise and easier to understand. In declarative programming, many low-level operational details are hidden, handled by the runtime environment or framework.

In One Sentence

Declarative programming leverages well-encapsulated tools to express intentions for program writing, while imperative delves into details, specifying concrete steps to achieve goals. Therefore, declarative programming is more suitable for large systems, often built on certain infrastructures, while imperative is more suited for small, prototype designs.