Exercise Optionals 01

Author: SteffenLm

.github/workflows/format.yml

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+name: format and commit all java files
+
+on:
+  workflow_dispatch:
+  push:
+    branches:
+      - 'exercises/**'
+      - 'solutions/**'
+
+jobs:
+  formatting:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-java@v3
+        with:
+          java-version: '17'
+          distribution: 'temurin'
+      - uses: axel-op/googlejavaformat-action@v3

.gitignore

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+# Compiled class file
+*.class
+
+# Log file
+*.log
+
+# BlueJ files
+*.ctxt
+
+# Mobile Tools for Java (J2ME)
+.mtj.tmp/
+
+# Package Files #
+*.jar
+*.war
+*.nar
+*.ear
+*.zip
+*.tar.gz
+*.rar
+
+# virtual machine crash logs, see http://www.java.com/en/download/help/error_hotspot.xml
+hs_err_pid*

Author.java

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+public record Author(String Name) {}

Book.java

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+public record Book(String title) {}

BookCollection.java

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+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map.Entry;
+
+public record BookCollection(HashMap<Author, List<Book>> collection) {
+
+  public void addAuthor(Author author) throws DuplicateKeyException {
+    if (collection.containsKey(author)) {
+      throw new DuplicateKeyException();
+    }
+
+    collection.put(author, new ArrayList<>());
+  }
+
+  public void addBook(Author author, Book book) {
+    collection.get(author).add(book);
+  }
+
+  public Book getBookByTitle(String title) {
+    for (List<Book> books : collection.values()) {
+      for (Book b : books) {
+        if (b.title().equals(title)) {
+          return b;
+        }
+      }
+    }
+    return null;
+  }
+
+  public Author getMostDiligentAuthor() {
+    Author mostDiligentAuthor = null;
+    int mostBooks = 0;
+    for (Entry<Author, List<Book>> entry : collection.entrySet()) {
+      if (entry.getValue().size() > mostBooks) {
+        mostDiligentAuthor = entry.getKey();
+        mostBooks = entry.getValue().size();
+      }
+    }
+    return mostDiligentAuthor;
+  }
+}

DuplicateKeyException.java

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+public class DuplicateKeyException extends Exception {}

Exercise.java

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+import java.util.HashMap;
+
+public class Exercise {
+
+  public static void main(String[] args) {
+    BookCollection collection = new BookCollection(new HashMap<>());
+
+    try {
+      collection.addAuthor(new Author("Stephen King"));
+      collection.addAuthor(new Author("George RR Martin"));
+    } catch (DuplicateKeyException e) {
+      e.printStackTrace();
+    }
+
+    collection.addBook(new Author("Stephen King"), new Book("Es"));
+    collection.addBook(new Author("Stephen King"), new Book("Sie"));
+    collection.addBook(new Author("George RR Martin"), new Book("Das Lied von Eis und Feuer 1"));
+    collection.addBook(new Author("George RR Martin"), new Book("Das Lied von Eis und Feuer 2"));
+    collection.addBook(new Author("George RR Martin"), new Book("Das Lied von Eis und Feuer 3"));
+    collection.addBook(new Author("George RR Martin"), new Book("Das Lied von Eis und Feuer 4"));
+    collection.addBook(new Author("George RR Martin"), new Book("Das Lied von Eis und Feuer 5"));
+    collection.addBook(new Author("George RR Martin"), new Book("Das Lied von Eis und Feuer 6"));
+
+    System.out.println(collection.getBookByTitle("Das Lied von Eis und Feuer 5"));
+    System.out.println(collection.getMostDiligentAuthor());
+  }
+}