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Commit 0e5f3d6

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Merge pull request #45 from bobocode-projects/GP-47-Migrate_lambda-math-functions
GP-47 Migrate lambda-math-functions
2 parents 5b41a24 + ccf7b46 commit 0e5f3d6

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package com.bobocode.lambda_math_functions;
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import com.bobocode.util.ExerciseNotCompletedException;
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import java.util.HashMap;
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import java.util.Map;
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import java.util.function.Function;
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/**
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* FunctionMap is an API that allows you to store and retrieve functions by string name. FunctionMap are stored in a
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* HashMap, where the key is a function name, and the value is a Function<T,R> instance
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*/
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public class FunctionMap<T, R> {
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private Map<String, Function<T, R>> functionMap;
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FunctionMap() {
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functionMap = new HashMap<>();
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}
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public void addFunction(String name, Function<T, R> function) {
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functionMap.put(name, function);
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}
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public Function<T, R> getFunction(String name) {
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if (functionMap.containsKey(name)) {
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return functionMap.get(name);
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} else {
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throw new ExerciseNotCompletedException();
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}
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}
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}
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package com.bobocode.lambda_math_functions;
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public class Functions {
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/**
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* A static factory method that creates an integer function map with basic functions:
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* - abs (absolute value)
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* - sgn (signum function)
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* - increment
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* - decrement
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* - square
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*
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* @return an instance of {@link FunctionMap} that contains all listed functions
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*/
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public static FunctionMap<Integer, Integer> intFunctionMap() {
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FunctionMap<Integer, Integer> intFunctionMap = new FunctionMap<>();
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// todo: add simple functions to the function map (abs, sgn, increment, decrement, square)
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return intFunctionMap;
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}
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}
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package com.bobocode.lambda_math_functions;
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public class InvalidFunctionNameException extends RuntimeException {
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public InvalidFunctionNameException(String functionName) {
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super("Function " + functionName + " doesn't exist.");
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}
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}
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# <img src="https://raw.githubusercontent.com/bobocode-projects/resources/master/image/logo_transparent_background.png" height=50/>Math functions exercise 💪
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Improve your lambda and method reference skills
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### Task
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**FunctionMap** is an API that allows you to store and retrieve math functions by string name. Your job is to implement the *todo* section of `Functions.java` class using **Lambda expressions and method reference**, so all tests in `FunctionsTest.java` should pass
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### Pre-conditions ❗
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You're supposed to be familiar with Java 8
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### How to start ❓
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* Just clone the repository and start implementing the **todo** section, verify your changes by running tests
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* If you don't have enough knowledge about this domain, check out the [links below](#related-materials-information_source)
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* Don't worry if you got stuck, checkout the [exercise/completed](to do) branch and see the final implementation
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### Related materials i️
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* [Lambda tutorial](to do) <img src="https://raw.githubusercontent.com/bobocode-projects/resources/master/image/logo_transparent_background.png" height=20/>
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* [State of lambda (JSR 335)](http://htmlpreview.github.io/?https://github.com/bobocode-projects/resources/blob/master/java8/lambda/sotl.html)
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package com.bobocode.lambda_math_functions;
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import org.junit.jupiter.api.*;
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import java.util.function.Function;
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import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
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import static org.assertj.core.api.AssertionsForClassTypes.assertThatExceptionOfType;
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@TestMethodOrder(MethodOrderer.OrderAnnotation.class)
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public class FunctionsTest {
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private FunctionMap<Integer, Integer> integerFunctionMap;
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@BeforeEach
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public void init() {
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integerFunctionMap = Functions.intFunctionMap();
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}
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@Test
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@Order(7)
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void squareFunction() {
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Function<Integer, Integer> squareFunction = integerFunctionMap.getFunction("square");
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int result = squareFunction.apply(5);
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assertThat(result).isEqualTo(25);
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}
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@Test
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@Order(1)
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void absFunction() {
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Function<Integer, Integer> absFunction = integerFunctionMap.getFunction("abs");
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int result = absFunction.apply(-192);
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assertThat(result).isEqualTo(192);
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}
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@Test
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@Order(5)
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void incrementFunction() {
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Function<Integer, Integer> incrementFunction = integerFunctionMap.getFunction("increment");
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int result = incrementFunction.apply(399);
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assertThat(result).isEqualTo(400);
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}
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@Test
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@Order(6)
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void destDecrementFunction() {
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Function<Integer, Integer> decrementFunction = integerFunctionMap.getFunction("decrement");
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int result = decrementFunction.apply(800);
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assertThat(result).isEqualTo(799);
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}
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@Test
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@Order(2)
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void signFunctionOnNegativeValue() {
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Function<Integer, Integer> signFunction = integerFunctionMap.getFunction("sgn");
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int result = signFunction.apply(-123);
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assertThat(result).isEqualTo(-1);
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}
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@Test
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@Order(3)
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void signFunctionOnPositiveValue() {
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Function<Integer, Integer> signFunction = integerFunctionMap.getFunction("sgn");
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int result = signFunction.apply(23);
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assertThat(result).isEqualTo(1);
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}
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@Test
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@Order(4)
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void signFunctionOnZero() {
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Function<Integer, Integer> signFunction = integerFunctionMap.getFunction("sgn");
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int result = signFunction.apply(0);
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assertThat(result).isEqualTo(0);
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}
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@Test
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@Order(8)
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void getUnknownFunction() {
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assertThatExceptionOfType(InvalidFunctionNameException.class).isThrownBy(()
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-> integerFunctionMap.getFunction("sqrt"));
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}
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}

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