HashMap - Searching Library Program By Book Index

I'm trying to search a library program by book index and running into some trouble with my HashMap. Here's the code in question:

Java Code:

public String searchByBookIndex(int input) {
NumberFormat fmt = NumberFormat.getCurrencyInstance();
Map<Integer, Book> bookMap = new HashMap<>();
for (int i = 0; i < author.booksByAuthor.size(); i++) {
bookMap.put(author.booksByAuthor.get(i).getBookIndex(), book);

[Code] ....

The search itself works fine; however, the problem is that the values of everything in the HashMap are overwritten by the last book entry. For example, let's say there are four books (index in parenthesis):

The Book (1), A Wonderful Book (2), A Great Book (3), A Bad Book (4).

Once the code above iterates, the HashMap out is this (via println):

1 = A Bad Book, 2 = A Bad Book, 3 = A Bad Book, 4 = A Bad Book.

What's causing this?