https://github.com/amigoscode/java-exercises

https://github.com/amigoscode/java-exercises

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• Host: GitHub
• URL: https://github.com/amigoscode/java-exercises
• Owner: amigoscode
• Created: 2026-03-08T07:05:51.000Z (5 months ago)
• Default Branch: main
• Last Pushed: 2026-06-29T13:28:24.000Z (28 days ago)
• Last Synced: 2026-06-29T15:19:27.146Z (28 days ago)
• Language: Java
• Size: 227 KB
• Stars: 1
• Watchers: 0
• Forks: 4
• Open Issues: 12
• Metadata Files:
  • Readme: README.md

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README

          
# Amigoscode Java Exercises

Guided hands-on exercises for the Java learning path on

[Amigoscode Academy](https://skool.com/amigoscode-academy).

## Tech Stack

- Java 25

- Maven

- JUnit 5, AssertJ & Mockito (for testing exercises)

## Branches

| Branch | Description |

|--------|-------------|

| `main` | Base setup |

| `exercises` | All exercises with TODOs |

| `solutions` | Completed solutions |

## How to Use

1. Checkout the exercises branch:

   ```bash

   git checkout exercises

   ```

2. Open the project in IntelliJ IDEA

3. Follow the exercises below in order - each course is a package

4. Use the **TODO tool window** (`View > Tool Windows > TODO`) to jump to exercise locations in the code

5. Stuck? Check the solutions branch:

   ```bash

   git checkout solutions

   ```

## Prerequisites

**Java 25 is required.** This project will not compile with older Java versions. Make sure you have Java 25 installed before starting.

You can check your Java version with:

```bash

java -version

```

## Course Order

The exercises follow the Java roadmap in this recommended order:

| # | Package | Course(s) | Exercises |

|---|---------|-----------|-----------|

| 1 | `beginners` | Java For Beginners | 69 |

| 2 | `developers` | Java For Developers | 130 |

| 3 | `oop` | Object Oriented Programming | 95 |

| 4 | `datastructures` | Data Structures | 99 |

| 5 | `generics` | Generics | 70 |

| 6 | `functionalinterfaces` | Functional Interfaces | 76 |

| 7 | `streams` | Streams Essentials + Java Streams | 152 |

| 8 | `testing` | Unit Testing Essentials + Unit Testing + Mockito | 126 |

| **Total** | | **11 courses** | **817** |

## Exercise Breakdown

Java For Beginners (69 exercises)

| # | File | TODOs | Topic |

|---|------|-------|-------|

| 01 | `beginners/thebasics/Variables.java` | 7 | Variable declaration and data types |

| 02 | `beginners/thebasics/TypeCasting.java` | 6 | Implicit/explicit casting and type conversion |

| 03 | `beginners/thebasics/Operators.java` | 7 | Arithmetic, comparison, logical, and ternary operators |

| 04 | `beginners/thebasics/StringExercises.java` | 8 | String methods (length, substring, split, equals) |

| 05 | `beginners/thebasics/ArrayExercises.java` | 7 | Array declaration, access, iteration, and summing |

| 06 | `beginners/thebasics/ConditionalStatements.java` | 7 | if/else, switch statements, switch expressions |

| 07 | `beginners/thebasics/LoopExercises.java` | 8 | for, while, do-while, enhanced for, nested loops |

| 08 | `beginners/thebasics/MethodExercises.java` | 7 | Method creation, return types, overloading |

| 09 | `beginners/thebasics/ScannerExercises.java` | 6 | Reading user input with Scanner |

| 10 | `beginners/thebasics/MiniProject.java` | 6 | Simple calculator combining all concepts |

Java For Developers (130 exercises)

| # | File | TODOs | Topic |

|---|------|-------|-------|

| 01 | `developers/loops/LoopExercises.java` | 7 | Nested loops, break/continue, patterns |

| 02 | `developers/conditionals/IfStatements.java` | 6 | Ternary, complex conditions, switch expressions |

| 03 | `developers/packages/PackageDemo.java` | 5 | Imports, static imports, fully qualified names |

| 04 | `developers/accessmodifiers/AccessModifiers.java` | 6 | public, private, protected, default |

| 05 | `developers/accessmodifiers/AccessDemo.java` | 5 | Accessing modifiers from another class |

| 06 | `developers/methods/MethodOverloading.java` | 7 | Method overloading with different parameters |

| 07 | `developers/methods/VarArgs.java` | 6 | Variable-length arguments |

| 08 | `developers/strings/StringMethods.java` | 8 | equals, compareTo, contains, replace, split |

| 09 | `developers/strings/StringBuilderExercises.java` | 6 | StringBuilder operations |

| 10 | `developers/dates/DateExercises.java` | 7 | LocalDate, LocalDateTime, formatting, parsing |

| 11 | `developers/bigdecimal/BigDecimalExercises.java` | 6 | BigDecimal arithmetic and comparisons |

| 12 | `developers/userinput/UserInputExercises.java` | 6 | Scanner with validation |

| 13 | `developers/exceptions/TryCatch.java` | 7 | try-catch-finally, multi-catch, try-with-resources |

| 14 | `developers/exceptions/CustomException.java` | 6 | Custom checked and unchecked exceptions |

| 15 | `developers/files/FileReading.java` | 6 | Reading files with Files and BufferedReader |

| 16 | `developers/files/FileWriting.java` | 6 | Writing files with Files and BufferedWriter |

| 17 | `developers/classes/ClassesAndObjects.java` | 7 | Classes, constructors, toString, equals |

| 18 | `developers/classes/EnumExercises.java` | 6 | Enums with fields, constructors, methods |

| 19 | `developers/staticmembers/StaticExercises.java` | 6 | Static fields, methods, factory methods |

| 20 | `developers/nullhandling/OptionalExercises.java` | 7 | Optional.of, ofNullable, map, flatMap |

Object Oriented Programming (95 exercises)

| # | File | TODOs | Topic |

|---|------|-------|-------|

| 01 | `oop/encapsulation/BankAccount.java` | 7 | Private fields, getters/setters, validation |

| 02 | `oop/encapsulation/ImmutablePerson.java` | 6 | Immutable class with final fields |

| 03 | `oop/inheritance/Animal.java` | 5 | Base class with fields and methods |

| 04 | `oop/inheritance/Dog.java` | 6 | Extending, super(), overriding methods |

| 05 | `oop/inheritance/Vehicle.java` | 5 | Base class for vehicle hierarchy |

| 06 | `oop/inheritance/ElectricCar.java` | 6 | Extending, constructor chaining, override |

| 07 | `oop/abstractclasses/Shape.java` | 5 | Abstract class and abstract methods |

| 08 | `oop/abstractclasses/Circle.java` | 5 | Implementing abstract methods |

| 09 | `oop/abstractclasses/Rectangle.java` | 5 | Implementing abstract methods |

| 10 | `oop/abstractclasses/Employee.java` | 7 | Abstract hierarchy with polymorphism |

| 11 | `oop/polymorphism/PaymentProcessor.java` | 7 | Interface, multiple implementations |

| 12 | `oop/polymorphism/ShapeCalculator.java` | 6 | Polymorphic methods, instanceof |

| 13 | `oop/dependencyinjection/NotificationService.java` | 7 | Constructor injection pattern |

| 14 | `oop/dependencyinjection/OrderProcessor.java` | 6 | Depend on abstractions |

| 15 | `oop/solid/SolidExercises.java` | 8 | All 5 SOLID principles |

Data Structures (99 exercises)

| # | File | TODOs | Topic |

|---|------|-------|-------|

| 01 | `datastructures/arrays/ArrayBasics.java` | 7 | Create, fill, search, sort arrays |

| 02 | `datastructures/arrays/TwoDArrays.java` | 6 | 2D array traversal (matrix) |

| 03 | `datastructures/arraylist/ArrayListBasics.java` | 7 | Add, remove, contains, iterate |

| 04 | `datastructures/arraylist/ArrayListOperations.java` | 7 | Sort, reverse, max, subList, toArray |

| 05 | `datastructures/stacks/StackExercises.java` | 7 | Push, pop, peek, balanced brackets |

| 06 | `datastructures/queues/QueueExercises.java` | 7 | Queue, PriorityQueue operations |

| 07 | `datastructures/linkedlists/LinkedListExercises.java` | 7 | addFirst, addLast, Iterator |

| 08 | `datastructures/linkedlists/LinkedListVsArrayList.java` | 5 | Performance comparison |

| 09 | `datastructures/sets/HashSetExercises.java` | 7 | Add, contains, remove duplicates |

| 10 | `datastructures/sets/TreeSetExercises.java` | 6 | Sorted set, subSet, headSet |

| 11 | `datastructures/maps/HashMapExercises.java` | 8 | put, get, containsKey, iterate |

| 12 | `datastructures/maps/HashMapWordCount.java` | 6 | Word frequency counter |

| 13 | `datastructures/maps/TreeMapExercises.java` | 6 | Sorted map operations |

| 14 | `datastructures/maps/MapAdvanced.java` | 6 | computeIfAbsent, merge, Map.of |

| 15 | `datastructures/challenge/DataStructureChallenge.java` | 7 | Mini project with multiple structures |

Generics (70 exercises)

| # | File | TODOs | Topic |

|---|------|-------|-------|

| 01 | `generics/classcastexception/ClassCastProblem.java` | 5 | Why generics are needed |

| 02 | `generics/typeparameters/TypeParameterBasics.java` | 6 | Generic class Container<T> |

| 03 | `generics/genericclasses/Box.java` | 6 | Generic Box<T> class |

| 04 | `generics/genericclasses/Pair.java` | 7 | Two type parameters Pair<K,V> |

| 05 | `generics/genericmethods/GenericMethods.java` | 7 | Generic static methods |

| 06 | `generics/genericmethods/GenericSwap.java` | 5 | Generic swap and reverse |

| 07 | `generics/boundedtypes/UpperBound.java` | 7 | <T extends Number> |

| 08 | `generics/boundedtypes/MultipleBounds.java` | 5 | Multiple type bounds |

| 09 | `generics/wildcards/UnboundedWildcard.java` | 5 | List<?> |

| 10 | `generics/wildcards/UpperBoundedWildcard.java` | 6 | <? extends Number> |

| 11 | `generics/wildcards/LowerBoundedWildcard.java` | 6 | <? super Integer> |

| 12 | `generics/typeerasure/TypeErasureDemo.java` | 5 | Type erasure behavior |

Functional Interfaces (76 exercises)

| # | File | TODOs | Topic |

|---|------|-------|-------|

| 01 | `functionalinterfaces/gettingstarted/FunctionalInterfaceBasics.java` | 6 | @FunctionalInterface and lambdas |

| 02 | `functionalinterfaces/gettingstarted/LambdaExpressions.java` | 7 | Lambda syntax and usage |

| 03 | `functionalinterfaces/gettingstarted/MethodReferences.java` | 6 | Static, instance, constructor refs |

| 04 | `functionalinterfaces/functionalinterfaces/FunctionExercise.java` | 7 | Function, andThen, compose |

| 05 | `functionalinterfaces/functionalinterfaces/BiFunctionExercise.java` | 5 | BiFunction |

| 06 | `functionalinterfaces/functionalinterfaces/ConsumerExercise.java` | 7 | Consumer, BiConsumer |

| 07 | `functionalinterfaces/functionalinterfaces/PredicateExercise.java` | 7 | Predicate, and/or/negate |

| 08 | `functionalinterfaces/functionalinterfaces/SupplierExercise.java` | 6 | Supplier for lazy creation |

| 09 | `functionalinterfaces/extending/ExtendingInterfaces.java` | 6 | Extending functional interfaces |

| 10 | `functionalinterfaces/extending/CombinatorPattern.java` | 7 | Validation combinator pattern |

| 11 | `functionalinterfaces/callbacks/CallbackExercise.java` | 6 | Callback pattern with Consumer |

| 12 | `functionalinterfaces/callbacks/EventProcessor.java` | 6 | Event-driven processing |

Java Streams (152 exercises)

| # | File | TODOs | Topic |

|---|------|-------|-------|

| 01 | `streams/basics/CreatingStreams.java` | 6 | Stream.of, Arrays.stream, generate |

| 02 | `streams/basics/FilterBasics.java` | 6 | Filtering lists |

| 03 | `streams/basics/MapBasics.java` | 6 | Mapping/transforming elements |

| 04 | `streams/basics/ForEachAndCollect.java` | 6 | forEach, collect to List/Set |

| 05 | `streams/basics/ReduceBasics.java` | 6 | Reduce operations |

| 06 | `streams/intstreams/IntStreamBasics.java` | 6 | IntStream.range, sum, average |

| 07 | `streams/intstreams/IntStreamIterate.java` | 5 | IntStream.iterate, LongStream |

| 08 | `streams/minmax/MinMax.java` | 6 | Finding min/max with Comparator |

| 09 | `streams/duplicates/DistinctExercise.java` | 6 | distinct(), collect to Set |

| 10 | `streams/filtering/FilterExercise.java` | 7 | Complex filter conditions |

| 11 | `streams/filtering/TakeWhileDropWhile.java` | 6 | takeWhile, dropWhile |

| 12 | `streams/filtering/FindAndMatch.java` | 7 | findFirst, anyMatch, allMatch |

| 13 | `streams/transformations/MapExercise.java` | 6 | Map objects to different types |

| 14 | `streams/transformations/FlatMapExercise.java` | 7 | Flatten nested structures |

| 15 | `streams/transformations/ReduceExercise.java` | 6 | Custom reduce operations |

| 16 | `streams/statistics/CountMinMax.java` | 6 | count, min, max on objects |

| 17 | `streams/statistics/AverageAndSum.java` | 6 | mapToInt, average, sum |

| 18 | `streams/statistics/SummaryStatistics.java` | 5 | IntSummaryStatistics |

| 19 | `streams/statistics/GroupingBy.java` | 7 | Collectors.groupingBy |

| 20 | `streams/statistics/GroupingAndCounting.java` | 6 | groupingBy + counting |

| 21 | `streams/sorting/SortingExercise.java` | 7 | sorted() with Comparator |

| 22 | `streams/joiningstrings/JoiningExercise.java` | 5 | Collectors.joining |

| 23 | `streams/collectors/CollectorsExercise.java` | 7 | toMap, partitioningBy, teeing |

| 24 | `streams/understanding/LazyStreams.java` | 5 | Lazy evaluation, short-circuiting |

| 25 | `streams/challenge/StreamsChallenge.java` | 8 | Full pipeline challenge |

Unit Testing + Mockito (126 exercises)

**Source classes** (in `src/main/java`):

| File | Description |

|------|-------------|

| `testing/firsttest/Calculator.java` | Calculator (add, subtract, multiply, divide) |

| `testing/assertions/StringUtils.java` | String utilities (palindrome, reverse, capitalize) |

| `testing/scenarios/GradeCalculator.java` | Grade calculator (score to letter grade) |

| `testing/assertj/Person.java` | Person class for AssertJ exercises |

| `testing/parameterized/EmailValidator.java` | Email validation |

| `testing/exceptions/BankAccount.java` | Bank account with exception handling |

| `testing/tdd/PasswordValidator.java` | Empty - implement via TDD |

| `testing/tdd/ShippingCostCalculator.java` | Empty - implement via TDD |

| `testing/mocking/*.java` | Interfaces and classes for mocking exercises |

**Test classes** (in `src/test/java`):

| # | File | TODOs | Topic |

|---|------|-------|-------|

| 01 | `testing/firsttest/CalculatorTest.java` | 7 | First unit test, assertEquals |

| 02 | `testing/assertions/StringUtilsTest.java` | 7 | assertTrue, assertFalse, assertAll |

| 03 | `testing/assertions/AssertThrowsTest.java` | 6 | assertThrows, exception messages |

| 04 | `testing/scenarios/GradeCalculatorTest.java` | 8 | Test scenarios and boundaries |

| 05 | `testing/junitfeatures/JunitFeaturesTest.java` | 8 | BeforeEach, Nested, Repeated, Tags |

| 06 | `testing/assertj/PersonTest.java` | 8 | AssertJ fluent assertions |

| 07 | `testing/parameterized/EmailValidatorTest.java` | 6 | @ParameterizedTest, @ValueSource |

| 08 | `testing/parameterized/CsvSourceTest.java` | 5 | @CsvSource, @CsvFileSource |

| 09 | `testing/exceptions/BankAccountTest.java` | 7 | assertThatThrownBy |

| 10 | `testing/tdd/PasswordValidatorTest.java` | 8 | TDD - write tests first |

| 11 | `testing/tdd/ShippingCostCalculatorTest.java` | 6 | TDD exercise |

| 12 | `testing/mocking/FirstMockTest.java` | 6 | @Mock, when/thenReturn, verify |

| 13 | `testing/mocking/MatchersTest.java` | 6 | any(), argThat(), eq() |

| 14 | `testing/mocking/VerifyInteractionsTest.java` | 7 | verifyNoInteractions, times, never |

| 15 | `testing/mocking/ArgumentCaptorTest.java` | 6 | ArgumentCaptor, @Captor |

| 16 | `testing/mocking/BDDMockitoTest.java` | 6 | given/willReturn, then/should |

| 17 | `testing/mocking/AdvancedMockingTest.java` | 7 | Answer, InOrder, spy, timeout |

| 18 | `testing/mocking/ClockMockingTest.java` | 6 | Mock Clock for time-dependent logic |

| 19 | `testing/mocking/ProductServiceTest.java` | 7 | Full mocking exercise |

## Community

Join the [Amigoscode Academy](https://skool.com/amigoscode) to get help,

share your progress, and connect with other learners.