Java SE 11 Developer study plan

Write and compile one-file programs with java directly (no explicit javac step) and explain the source-file launch rules for classes with a main method.

Demonstrate primitive widening, narrowing casts, autoboxing and unboxing in a scratch class, predicting each output before running it.

Declare and initialize local variables inside if/for/switch blocks and document the definite-assignment rules you hit as compile errors.

Build a Predicate, Function, Supplier and Consumer lambda for the same domain object and chain them with andThen/and.

Convert a List of objects into a Stream, filter, map to a different type, and collect with Collectors.toList, toSet and joining.

Use Optional correctly with map, flatMap, orElseThrow and ifPresent, and remove at least two null checks from earlier code.

Compare ArrayList, HashSet, TreeSet and ArrayDeque by writing code that shows ordering, duplicates and equals/hashCode effects.

Implement Comparable and a Comparator with comparing/thenComparing, and sort the same collection both ways.

Use Map methods getOrDefault, putIfAbsent, compute, merge and replaceAll to rewrite a loop-based counting routine.

Iterate collections with Iterator and remove safely, and reproduce then fix a ConcurrentModificationException.

Create threads with Runnable, Thread and an ExecutorService, and shut the pool down with shutdown/awaitTermination.

Demonstrate a race condition on a shared counter and fix it with AtomicInteger and with synchronized.

Design a small class hierarchy using an abstract class, an interface with a default method, and an interface with a static method.

Apply encapsulation rules: private fields, accessors, protected visibility across packages, and explain why a final field must be assigned in every constructor.

Write try/catch/finally and try-with-resources blocks, and show the difference in behavior when finally itself throws.

Create a custom checked exception and a custom unchecked exception and justify which call sites declare throws.

Use assert with -ea and explain when assertion failure is inappropriate for validating user input.

Write if/else if, switch on String, int and an enum, and convert one switch statement to an arrow-form switch expression with yield.

Implement while, do-while, classic for, enhanced for and labeled break/continue over nested loops.

Use var in local variable declarations, for-loop indexes and try-with-resources, and list the places where var is illegal.

Trace and predict output for a nested-loop program before executing it.

Create a multi-module project with module-info.java using requires, exports, opens and provides ... with, and compile/run it from the command line.

Diagnose one module not found and one package is not visible error and record the exact fix for each.

Read and write text files with Files.newBufferedReader, Files.writeString and Files.lines, using try-with-resources.

Walk a directory tree with Files.walk/Files.find, filter by extension, and copy selected files with Files.copy.

Serialize and deserialize one object with ObjectOutputStream/ObjectInputStream and note the serialVersionUID requirement.

Harden input handling: validate with a whitelist, avoid building SQL or shell strings by concatenation, and use PreparedStatement-style parameterization in a mock example.

Demonstrate defensive copying of mutable fields and arrays returned from accessors, and use char[] plus Arrays.fill for clearing password data.

Format dates, numbers and currency with DateTimeFormatter, NumberFormat and Locale, and parse a localized date string.

Load a ResourceBundle with a properties file for two locales and switch locales at runtime.

Declare and read a custom annotation with @Retention(RetentionPolicy.RUNTIME) via reflection, and mark a deprecated method with @Deprecated.

Re-implement one earlier exercise using CompletableFuture chaining and compare it to the executor version.

Review every domain checklist and write a one-line self-test question per objective you still cannot answer from memory.

Complete two timed 50-question mixed practice sets under exam conditions and log wrong answers by domain.

Re-code the three weakest objectives from a blank file without notes.