Mid-Level Developer 路 2-5 years
Mid-level interviews focus on trade-offs and ownership. Interviewers want to see that you have hit real problems such as slow queries, race conditions or re-render storms, and know how to reason your way through them.
104 questions
Prop drilling is passing props through several layers of components that do not use them just to reach a deeply nested child; you avoid it with composition, the Context API or a state management library.
Relative offsets an element from its normal place; absolute positions it against the nearest positioned ancestor; fixed is against the viewport; sticky sits in normal flow until a scroll threshold, then sticks.
Flexbox is one-dimensional (a row or a column). CSS Grid is two-dimensional (rows and columns at once). Use Flexbox for alignment along a line; use Grid when the layout is a real 2D structure.
Specificity is the score the browser uses to decide which rule wins: inline styles beat IDs, IDs beat classes/attributes/pseudo-classes, and those beat elements. When scores tie, the last rule in the source wins.
any turns off checking. unknown is a type-safe any: you must narrow it before use. never means a value cannot exist, used for exhaustive checks and functions that always throw.
Generics are type parameters: they let a function, class or type work with many types while keeping the relationship between inputs and outputs, instead of falling back to any.
A union (A | B) is a value that is one of the members. An intersection (A & B) is a value that must satisfy both types at once.
Utility types are built-in helpers that transform an existing type: Partial makes every field optional, Required the opposite, Pick keeps a set of keys, Omit removes them, and Record builds a key/value map.
Use a subquery that takes the MAX salary below the overall MAX, or use DENSE_RANK() and pick rank 2, which also handles ties and generalises to the Nth highest.
Find duplicates with GROUP BY and HAVING COUNT(*) > 1, then delete them by numbering rows within each duplicate group with ROW_NUMBER() and removing every row after the first.
Normalization is organising tables to reduce redundancy and update anomalies: 1NF means atomic values, 2NF removes partial dependencies on part of a composite key, and 3NF removes dependencies between non-key columns.
An abstract class can hold state, constructors and partial implementation but a class can inherit only one, while an interface defines a contract that a class can implement many of.
Boxing converts a value type to object by allocating it on the heap, and unboxing converts it back; both add allocations and casts, so avoid them in hot code paths.
LINQ (Language Integrated Query) lets you query collections, databases and XML with a consistent syntax, and deferred execution means a query does not run when you define it but when you enumerate the results.
An abstract class can have instance fields, constructors and a mix of implemented and abstract methods but supports only single inheritance, while an interface defines a contract that a class can implement multiple times and, since Java 8, can include default methods.
ArrayList is backed by a resizable array with O(1) index access and O(n) insertion in the middle, while LinkedList is a doubly linked list with O(n) index access and O(1) insertion once you hold the node; in practice ArrayList is faster for most workloads.
Checked exceptions (subclasses of Exception other than RuntimeException) must be caught or declared with throws, while unchecked exceptions (RuntimeException and Error) do not have to be handled and usually signal programming bugs.
Java 8 introduced lambda expressions, functional interfaces, the Stream API for declarative collection processing, Optional to represent missing values, default methods in interfaces, method references and the java.time date and time API.
Default argument values are evaluated once when the function is defined, so a default list or dictionary is shared between every call that does not pass its own, causing data to leak between calls.
A shallow copy creates a new container but reuses the same nested objects, while a deep copy recursively copies everything so the new object is fully independent.