100+ Free Java SE 11 Developer Practice Questions

Working with Java Data Types, Operators, and String APIs

Use primitives and wrapper classes with operators, type promotion, and casting; handle text with String and StringBuilder, including Java 11 methods like isBlank and strip; and apply local variable type inference (var), including as a lambda parameter.

Controlling Program Flow

Create and use loops, if/else, and switch statements, including the enhanced for loop, labeled break and continue, do-while semantics, and String selectors in traditional switch.

Java Object-Oriented Approach

Declare and instantiate objects and nested classes; define fields, methods, constructors, and initializers; and apply inheritance, polymorphism, method hiding, interfaces with default methods, abstract classes, enums, and inner/anonymous classes.

Exception Handling

Use try/catch/finally, multi-catch with effectively final parameters, and try-with-resources on AutoCloseable resources; create custom checked and unchecked exceptions; and apply the checked-versus-unchecked rules.

Working with Arrays and Collections

Create and manipulate arrays (including jagged arrays), List, Set, Map, and Deque; use generics, bounded type parameters, and wildcards; sort with Comparator chains; and use immutable factory methods such as List.of and Map.getOrDefault.

Working with Streams and Lambda Expressions

Use lambdas, method references, and standard functional interfaces; build pipelines with filter, map, flatMap, reduce, and Collectors such as groupingBy and joining; use Optional and function composition; and understand stream laziness, short-circuiting, and single-use traversal.

Java Platform Module System

Declare modules with requires, requires transitive, exports, opens, uses, and provides...with; build modular and service-based applications; understand java.base, automatic modules, and open modules; and use migration tools like jdeps and jlink.

Concurrency

Create and manage threads; use ExecutorService, Runnable, Callable, and Future; apply synchronization and monitors, AtomicInteger, concurrent collections such as ConcurrentHashMap, and thread-pool factory methods, including correct shutdown semantics.

Java I/O API and NIO.2

Read and write console and file data with I/O streams and buffered readers; serialize and deserialize objects with transient and static field rules; and handle the file system with the java.nio.file Path and Files APIs.

Database Applications, Localization, and Annotations

Use the JDBC API with Connection, PreparedStatement, ResultSet, and executeUpdate; apply Locale, resource bundles, NumberFormat, MessageFormat, and DateTimeFormatter; and use core annotations such as @Override, @FunctionalInterface, @Deprecated(forRemoval), and @SuppressWarnings.

Secure Coding in Java SE Applications

Mitigate threats such as denial of service, code injection, and improper input validation; defend against SQL injection with parameterized PreparedStatements; use defensive copying to protect mutable state; and store secrets in char arrays rather than immutable Strings.