Stop Writing If-Else Trees: Use the State Pattern Instead

Have you ever looked at your code and found a huge mess of if-else statements that just keeps growing? As your program gets bigger, these if-else trees become harder to read, test, and change. There’s a better way to handle this problem: the State Pattern.

What’s Wrong With If-Else Trees?

Before we talk about the solution, let’s look at the problem. Here’s an example of code that uses many if-else statements to handle different states of a document:

public class Document {
    private String state = "DRAFT";
    
    public void publish() {
        if (state.equals("DRAFT")) {
            state = "PUBLISHED";
            System.out.println("Document published successfully!");
        } else if (state.equals("PUBLISHED")) {
            System.out.println("Document is already published!");
        } else if (state.equals("ARCHIVED")) {
            System.out.println("Cannot publish an archived document!");
        }
    }
    
    public void archive() {
        if (state.equals("DRAFT")) {
            System.out.println("Cannot archive a draft document!");
        } else if (state.equals("PUBLISHED")) {
            state = "ARCHIVED";
            System.out.println("Document archived successfully!");
        } else if (state.equals("ARCHIVED")) {…