Adaptive skill practice — find your level, get sharper.

Java practice

Predict the output — and learn Java’s sharp edges

Master Java by predicting what real code prints — int division truncating toward zero and silent 32-bit overflow, type-driven division (one double changes everything), char promotion to int codes, the bitwise operators including the unsigned >>>, String pool reference equality (== vs equals), the Integer autoboxing cache, collections and arrays, and the runtime exceptions. Answers are modeled on Java’s exact semantics (reference: Java 25 LTS) and verified against the JDK. Builds genuine fluency for interviews. Part of the Developer track.

• Meets you at your level — never too easy, never too hard.

• Adapts every question to how you’re doing.

• Tracks your level over time. Skill practice, not a test.

New here? Read the Java guide

A free 16-minute primer — the mental model, the mistakes beginners make, and what to practise first.

Curriculum

223 concepts across 26 chapters, from foundations through advanced practice — each one a concept the adaptive question bank can teach and test.

A. Types, values and variables

B. Conversions, promotion and casting

C. Operators and expression evaluation

D. Statements, control flow and definite assignment

E. Classes, construction and initialization

F. Interfaces, inheritance and polymorphism

G. The Object contract

H. Strings and text

I. Arrays

J. Records, enums, sealed types and pattern matching

K. Exceptions

L. Generics

M. Collections

N. Lambdas, method references and functional interfaces

O. Streams and collectors

P. Optional and null discipline

Q. Threads, the memory model and synchronization

R. java.util.concurrent and virtual threads

S. Dates and times

T. I/O, files and serialization

U. Class loading, linking and initialization

V. The JVM: memory, garbage collection and performance

W. Packages, modules and the toolchain

X. Annotations and reflection

Y. Java 25 language frontier

Z. Release cadence and support

View the full curriculum →

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