400 PHP Interview Questions with Answers 2026

Object-Oriented Design: SOLID principles, PSR-4, and advanced design patterns.

Web & API Ecosystem: JWT/OAuth, HTTP lifecycle, and Middleware.

Data & Scaling: PDO, Redis caching, query optimization, and transactions.

Security & DevOps: XSS/CSRF prevention, PHPUnit, Docker, and CI/CD.

B) They use the global keyword to access parent variables.

C) They require the use language construct to inherit variables from the parent scope by value (or reference).

D) They cannot access any variables outside their own local scope.

E) They only have access to superglobals like $_SESSION and $_GET.

F) They inherit variables from the parent scope only if the function is defined as static.

Correct Answer: C

Overall Explanation: In PHP, closures do not automatically capture variables from the surrounding scope. To utilize a variable from the parent scope inside the closure, you must explicitly pass it via the use clause.

Option Explanations:

B: Incorrect; global pulls from the global script scope, not the immediate parent/function scope.

C: Correct; This is the standard syntax for lexical scoping in PHP.

D: Incorrect; They can access external variables if explicitly imported.

E: Incorrect; All functions have access to superglobals, but closures can access more via use.

F: Incorrect; static closures actually prevent the automatic binding of $this.

Question 2: In the context of the SOLID principles, what is the primary goal of the "Interface Segregation Principle"?

B) A class should have only one reason to change.

C) Objects of a superclass should be replaceable with objects of its subclasses.

D) Depend upon abstractions, not concretions.

E) Clients should not be forced to depend upon interfaces that they do not use.

F) Every interface must be implemented by at least two distinct classes.

Correct Answer: E

Overall Explanation: The Interface Segregation Principle (ISP) advocates for splitting large, "fat" interfaces into smaller, more specific ones so that implementing classes only need to concern themselves with methods that are relevant to them.

Option Explanations:

B: Incorrect; This describes the Single Responsibility Principle.

C: Incorrect; This describes the Liskov Substitution Principle.

D: Incorrect; This describes the Dependency Inversion Principle.

E: Correct; This is the core definition of ISP.

F: Incorrect; There is no numerical requirement for implementations in SOLID.

Question 3: How does the yield keyword function within a PHP Generator?

B) It pauses function execution and returns a value to the caller, resuming from that point when called again.

C) It sends an immediate header redirect to the browser.

D) It is an alias for the return keyword in modern PHP versions.

E) It forces the garbage collector to clear the current function's memory.

F) It allows a function to return multiple values simultaneously as a standard array.

Correct Answer: B

Overall Explanation: Generators provide an easy way to implement iterators without the overhead of implementing a class. The yield keyword provides the value to the loop and "freezes" the state of the function.

Option Explanations:

B: Correct; This state-saving behavior is what makes generators memory-efficient.

C: Incorrect; header() handles redirects.

D: Incorrect; yield and return have very different behaviors in terms of state.

E: Incorrect; yield actually helps memory but isn't a GC trigger.

F: Incorrect; It returns a Generator object, not a standard array.

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