PHP Interview Questions

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PHP interviews typically probe three layers: whether you understand the language's quirks (type juggling, comparison operators, array semantics), whether you can reason about object-oriented design (interfaces vs. abstract classes, magic methods, composition), and whether you're current with modern PHP 8.x idioms (enums, match, named arguments, attributes). Strong candidates don't just recite syntax — they can explain *why* a language decision matters, such as why === exists alongside ==, or why readonly properties change how you design value objects.

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Cricket analogy: A cricket academy's final trial doesn't just test whether a recruit can bowl a yorker; it probes whether they understand field placements, captaincy decisions, and modern T20 tactics like the switch-hit, mirroring how PHP interviews probe quirks, OOP design, and PHP 8 idioms.

Language fundamentals

A classic opener is 'what's the difference between == and ===?' — == performs type coercion before comparing, which historically caused surprising results like '0' == false evaluating to true or numeric-looking strings comparing equal to numbers in ways developers didn't expect. === compares both value and type with no coercion, and is almost always the safer default. Another staple is explaining isset() vs. empty() vs. is_null(): isset() returns false for both unset and null variables, empty() additionally treats falsy values (0, '', '0', []) as empty, and is_null() strictly checks for null but throws a notice on an undefined variable.

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Cricket analogy: A loose umpiring rule that once let a batter given out on a technicality still be recalled if the crowd protested loudly was scrapped for a strict, evidence-only DRS review — much like =='s surprising coercion giving way to ==='s strict, predictable check.

OOP and modern PHP

Expect questions distinguishing interfaces (a contract with no implementation) from abstract classes (can provide partial implementation and shared state) and from traits (reusable method implementations mixed into unrelated class hierarchies, resolving PHP's lack of multiple inheritance). Interviewers also probe PHP 8-specific features: enums for type-safe fixed sets of values, match for strict, non-fallthrough branching that returns a value, named arguments for self-documenting calls, and the nullsafe operator (?->) for chaining optional lookups without verbose null checks.

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Cricket analogy: A tour contract (interface) just lists obligations like 'must be available for all five Tests,' while a county academy program (abstract class) actually provides some training infrastructure, and a specialist fielding-drill routine (trait) can be borrowed by players across different squads.

php

// Common interview snippet: predict the output
function demo(): void
{
    $a = '10';
    $b = 10;
    var_dump($a == $b);   // true  (type coercion)
    var_dump($a === $b);  // false (different types)
}

// Modern idiom worth mentioning: enum + match + nullsafe
enum Role: string
{
    case Admin = 'admin';
    case Editor = 'editor';
    case Viewer = 'viewer';
}

function permissionLevel(?User $user): string
{
    return match ($user?->role) {
        Role::Admin => 'full-access',
        Role::Editor => 'edit-access',
        Role::Viewer, null => 'read-only',
    };
}

Interviewers often ask you to walk through a foreach over an array by reference and explain a subtle bug: leaving a stray &$value reference bound after the loop, which then silently overwrites the last array element on a subsequent unrelated foreach reusing the same variable name. Being able to spot and explain this signals real hands-on experience, not just textbook knowledge.

Avoid answering 'why use PHP' or design questions with pure syntax dumps. Interviewers weight *reasoning* — trade-offs, when NOT to use a feature — much more heavily than the ability to recite a manual page from memory.

=== avoids PHP's type-coercion surprises that == can introduce; prefer it by default.
isset(), empty(), and is_null() differ in how they treat unset variables, null, and falsy values.
Interfaces define contracts; abstract classes share partial implementation and state; traits mix in reusable methods.
PHP 8.x staples to know cold: enums, match, named arguments, nullsafe operator, readonly properties, attributes.
Be ready to trace output of type-juggling snippets and explain foreach-by-reference pitfalls.
Interviewers value reasoning about trade-offs over rote syntax recall.

Practice what you learned

1. What does `$a === $b` check that `$a == $b` does not?

2. Which function returns true for a variable holding the value `0`?

3. What is the key difference between an interface and an abstract class in PHP?

4. What does the nullsafe operator (`?->`) do?

5. In a classic 'foreach by reference' bug, what causes data corruption in a later loop?

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PHP Interview Questions