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Commit 1baec88

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GP-24 update readme and structure
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# <img src="https://raw.githubusercontent.com/bobocode-projects/resources/master/image/logo_transparent_background.png" height=50/>Crazy lambda exercise :muscle:
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# <img src="https://raw.githubusercontent.com/bobocode-projects/resources/master/image/logo_transparent_background.png" height=50/>Lambda exercises :muscle:
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Improve your lambda skills
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### Task
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`CrazyLambdas` class consists of static methods that return various functions, operations and predicates.
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Your job is to implement the *todo* section of that class using **Lambda expressions** and **method reference**.
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To verify your implementation, run `CrazyLambdasTest.java`
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Every package contains **an exercise (interactive tutorial) on lambdas**, where you need to write code in order
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to complete the implementation. If you need more theory, you can **check [tutorial section](#tutorial)**.
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To verify your solution, you should **run a corresponding test :arrow_forward:.**
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### Pre-conditions :heavy_exclamation_mark:
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You're supposed to be familiar with Java 8
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### How to start :question:
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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** branch and see the final implementation
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### Related materials :information_source:
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* [Lambda tutorial](https://github.com/bobocode-projects/java-8-tutorial/tree/master/lambdas) <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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### Tutorial
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Java is an OOP language, so it always works with classes and **doesn't support standalone functions**.
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In case you want to **pass some function as a method parameter**, or **store some code into a variable**,
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you should use a *Functional Interface* and a *Lambda expression*.
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* A *Functional Interface (FI)* represents a **function signature**. It contains only one abstract method.
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* A *Lambda expression* represents a **function body**. Is an anonymous function that implements the abstract method
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of the functional interface
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The purpose of the lambda and functional interfaces is to **make it easier to create function objects**
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and provide an **ability to use some functional programming technics in Java.**
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A typical example is interface `Comparator<T>`:
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```java
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accounts.sort(new Comparator<Account>() {
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@Override
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public int compare(Account o1, Account o2) {
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return o1.getFirstName().compareTo(o2.getFirstName());
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}
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});
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```
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It can be easily simplified using lambda expression:
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```java
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accounts.sort((a1, a2) -> a1.getFirstName().compareTo(a2.getFirstName()));
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```
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In case you are calling some existing method inside the lambda, you can reference that method instead of actually
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calling it. This technique is called *Method Reference*. Combining it with usefull default method `comparing()`
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it can help you to simplify the code even more:
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```java
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accounts.sort(comparing(Account::getFirstName));
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```
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### Best practices
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* use **lambdas instead of anonymous classes**
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* **avoid lambda parameter types**, unless it can improve code readability
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* **keep lambda expression small** (1 line is the best option)
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* **always use `@FunctionalInterface` annotation** for custom functional interfaces
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* **prefer standard predefined functional interfaces** (`java.util.function`)
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* create a **custom FI**, in case it has some **specific contract**, and you can **benefit from self-descriptive name** and **default methods**
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* **use special FI for primitives** (e.g. `IntToDoubleFunction` instead of `Function<Integer, Double>`)
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* **prefer method reference** in all cases where it helps to improve readability
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### Related materials :information_source:
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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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* [Modern Java in Action](https://amzn.to/2KwUKW5) :green_book:
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* Passing code with behaviour parameterization - Chapter 2
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* Lambda expressions - Chapter 3
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* [Effective Java 3rd Edition](https://amzn.to/3mYA0U1) :blue_book:
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* Prefer Lambdas to anonymous classes – Item 42
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* Prefer method reference to lambdas - Item 43
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* Favor the use of standard functional interfaces - Item 44

‎6-0-functional-programming/src/main/java/com/bobocode/lambdas/CrazyLambdas.java renamed to ‎6-0-functional-programming/src/main/java/com/bobocode/lambdas/level2/CrazyLambdas.java

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package com.bobocode.lambdas;
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package com.bobocode.lambdas.level2;
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import com.bobocode.util.ExerciseNotCompletedException;
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import java.math.BigDecimal;
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import java.util.Map;
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import java.util.function.*;
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/**
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* {@link CrazyLambdas} is an exercise class. Each method returns a functional interface and it should be implemented
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* using either lambda or a method reference. Every method that is not implemented yet throws
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* {@link ExerciseNotCompletedException}.
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* <p>
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* TODO: remove exception and implement each method of this class using lambda or method reference
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*/
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public class CrazyLambdas {
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/**

‎6-0-functional-programming/src/main/java/com/bobocode/optionals/CrazyOptionals.java

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import com.bobocode.data.Accounts;
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import com.bobocode.model.Account;
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import com.bobocode.model.CreditAccount;
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import com.bobocode.optionals.exception.AccountNotFoundException;
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import com.bobocode.optionals.function.AccountProvider;
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import com.bobocode.optionals.function.AccountService;
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import com.bobocode.optionals.function.CreditAccountProvider;
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import com.bobocode.util.ExerciseNotCompletedException;
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import javax.annotation.Nonnull;
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import javax.annotation.Nullable;
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import java.util.Optional;
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import java.util.OptionalDouble;
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/**
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* {@link CrazyOptionals} is an exercise class. Each method represents some operation with a {@link Account} and
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* should be implemented using Optional API. Every method that is not implemented yet throws
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* {@link ExerciseNotCompletedException}.
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* <p>
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* TODO: remove exception and implement each method of this class using Optional API
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*/
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public class CrazyOptionals {
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/**
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* @return optional object that holds text
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*/
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public static Optional<String> optionalOfString(@Nullable String text) {
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throw new UnsupportedOperationException("Some people say that method does not work until you implement it");
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throw new ExerciseNotCompletedException();
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}
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/**
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* @param amount money to deposit
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*/
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public static void deposit(AccountProvider accountProvider, BigDecimal amount) {
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throw new UnsupportedOperationException("Some people say that method does not work until you implement it");
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throw new ExerciseNotCompletedException();
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}
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/**
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* @return optional object that holds account
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*/
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public static Optional<Account> optionalOfAccount(@Nonnull Account account) {
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throw new UnsupportedOperationException("Some people say that method does not work until you implement it");
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throw new ExerciseNotCompletedException();
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}
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/**
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* @return account from provider or defaultAccount
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*/
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public static Account getAccount(AccountProvider accountProvider, Account defaultAccount) {
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throw new UnsupportedOperationException("Some people say that method does not work until you implement it");
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throw new ExerciseNotCompletedException();
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}
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/**
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* @param accountService
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*/
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public static void processAccount(AccountProvider accountProvider, AccountService accountService) {
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throw new UnsupportedOperationException("Some people say that method does not work until you implement it");
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throw new ExerciseNotCompletedException();
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}
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/**
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* @return provided or generated account
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*/
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public static Account getOrGenerateAccount(AccountProvider accountProvider) {
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throw new UnsupportedOperationException("Some people say that method does not work until you implement it");
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throw new ExerciseNotCompletedException();
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}
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/**
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* @return optional balance
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*/
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public static Optional<BigDecimal> retrieveBalance(AccountProvider accountProvider) {
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throw new UnsupportedOperationException("Some people say that method does not work until you implement it");
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throw new ExerciseNotCompletedException();
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}
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/**
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* @return provided account
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*/
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public static Account getAccount(AccountProvider accountProvider) {
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throw new UnsupportedOperationException("Some people say that method does not work until you implement it");
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throw new ExerciseNotCompletedException();
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}
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/**
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* @return optional credit balance
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*/
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public static Optional<BigDecimal> retrieveCreditBalance(CreditAccountProvider accountProvider) {
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throw new UnsupportedOperationException("Some people say that method does not work until you implement it");
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throw new ExerciseNotCompletedException();
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}
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* @return optional gmail account
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*/
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public static Optional<Account> retrieveAccountGmail(AccountProvider accountProvider) {
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throw new UnsupportedOperationException("Some people say that method does not work until you implement it");
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throw new ExerciseNotCompletedException();
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}
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/**
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* @return account got from either accountProvider or fallbackProvider
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*/
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public static Account getAccountWithFallback(AccountProvider accountProvider, AccountProvider fallbackProvider) {
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throw new UnsupportedOperationException("Some people say that method does not work until you implement it");
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throw new ExerciseNotCompletedException();
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}
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/**
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* @return account with the highest balance
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*/
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public static Account getAccountWithMaxBalance(List<Account> accounts) {
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throw new UnsupportedOperationException("Some people say that method does not work until you implement it");
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throw new ExerciseNotCompletedException();
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}
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/**
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* @return the lowest balance values
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*/
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public static OptionalDouble findMinBalanceValue(List<Account> accounts) {
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throw new UnsupportedOperationException("Some people say that method does not work until you implement it");
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throw new ExerciseNotCompletedException();
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}
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/**
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* @param accountService
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*/
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public static void processAccountWithMaxBalance(List<Account> accounts, AccountService accountService) {
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throw new UnsupportedOperationException("Some people say that method does not work until you implement it");
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throw new ExerciseNotCompletedException();
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}
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/**
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* @return total credit balance
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*/
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public static double calculateTotalCreditBalance(List<CreditAccount> accounts) {
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throw new UnsupportedOperationException("Some people say that method does not work until you implement it");
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throw new ExerciseNotCompletedException();
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}
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}
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‎6-0-functional-programming/src/main/java/com/bobocode/optionals/AccountNotFoundException.java renamed to ‎6-0-functional-programming/src/main/java/com/bobocode/optionals/exception/AccountNotFoundException.java

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package com.bobocode.optionals;
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package com.bobocode.optionals.exception;
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public class AccountNotFoundException extends RuntimeException {
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public AccountNotFoundException(String message) {

‎6-0-functional-programming/src/main/java/com/bobocode/optionals/AccountProvider.java renamed to ‎6-0-functional-programming/src/main/java/com/bobocode/optionals/function/AccountProvider.java

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package com.bobocode.optionals;
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package com.bobocode.optionals.function;
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import com.bobocode.model.Account;
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‎6-0-functional-programming/src/main/java/com/bobocode/optionals/AccountService.java renamed to ‎6-0-functional-programming/src/main/java/com/bobocode/optionals/function/AccountService.java

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package com.bobocode.optionals;
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package com.bobocode.optionals.function;
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import com.bobocode.model.Account;
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‎6-0-functional-programming/src/main/java/com/bobocode/optionals/CreditAccountProvider.java renamed to ‎6-0-functional-programming/src/main/java/com/bobocode/optionals/function/CreditAccountProvider.java

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package com.bobocode.optionals;
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package com.bobocode.optionals.function;
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import com.bobocode.model.CreditAccount;
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