Java
Business logic
Write business rules with methods and conditions.
The borrowBook method
The borrowing logic: find the first available book in the list and set its available field to false. You scan the list with a for-each loop.
void borrowBook() {
for (Book b : books) {
if (b.available) {
b.available = false;
return;
}
}
}
When found, return exits the loop; this way only one book is borrowed. If no book is available, the method simply ends. This behavior will turn into throwing an error in the next lesson.
The returnBook method
To take back a borrowed book you write returnBook: find the first book with available == false and set it to true. The logic is the mirror of borrowBook.
void returnBook() {
for (Book b : books) {
if (!b.available) {
b.available = true;
return;
}
}
}
! takes the negation, so the borrowed book is found. In this lesson's code task you will write only borrowBook; returnBook is the mirror of the same logic and you can add it yourself if you want.
Exercise Write and call borrowBook
Add void borrowBook() to the Catalog class: iterate with for (Book b : books), set the first available book's available field to false and exit with return. In main call cat.borrowBook() and print cat.books.
Show example solution
// inside Catalog:
void borrowBook() {
for (Book b : books) {
if (b.available) {
b.available = false;
return;
}
}
}
// inside main:
cat.borrowBook();
System.out.println(cat.books);
Test yourself
-
Complete the for-each loop
for (____ b : books) {
if (b.available) { b.available = false; return; }
}
Show answer
for (Book b : books) {
if (b.available) { b.available = false; return; }
}
-
What does borrowBook do when it finds an available book?
- Sets available to false and exits with return
- Deletes the list
- Borrows all books
- Throws an error
Show answer
Sets available to false and exits with return — available is set to false and return exits the loop; only one book is borrowed.
-
Match each method to its behavior
- borrowBook
- available false
- returnBook
- available true
- addBook
- Add to list
- toString
- String representation
Next lesson: Error handling
