You should have fundamental knowledge about the Java language. You should install the following:

• An IDE (recommended, but not a must, is Apache NetBeans 11.x: https://netbeans.apache.org/)
• JDK 12 and Maven 3.3.x
• Additional third-party libraries will need to be installed at the right moment (nothing special)

You can download the example code files for this book from your account at www.packt.com. If you purchased this book elsewhere, you can visit www.packtpub.com/support and register to have the files emailed directly to you.

You can download the code files by following these steps:

1. Log in or register at www.packt.com.
2. Select the Support tab.
3. Click on Code Downloads.
4. Enter the name of the book in the Search box and follow the onscreen instructions.

Once the file is downloaded, please make sure that you unzip or extract the folder using the latest version of:

• WinRAR/7-Zip for Windows
• Zipeg/iZip/UnRarX for Mac
• 7-Zip/PeaZip for Linux

The code bundle for the book is also hosted on GitHub at https://github.com/PacktPublishing/Java-Coding-Problems. In case there's an update to the code, it will be updated on the existing GitHub repository.

We also have other code bundles from our rich catalog of books and videos available at https://github.com/PacktPublishing/. Check them out!

We also provide a PDF file that has color images of the screenshots/diagrams used in this book. You can download it here: https://static.packt-cdn.com/downloads/9781789801415_ColorImages.pdf.

To see the code being executed please visit the following link: http://bit.ly/2kSgFKf.

There are a number of text conventions used throughout this book.

CodeInText: Indicates code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles. Here is an example: "If the current character exists in the Map instance, then simply increase its occurrences by 1 with (character, occurrences+1)."

A block of code is set as follows:

public Map<Character, Integer> countDuplicateCharacters(String str) {

  Map<Character, Integer> result = new HashMap<>();

  // or use for(char ch: str.toCharArray()) { ... }
  for (int i = 0; i<str.length(); i++) {
    char ch = str.charAt(i); 

    result.compute(ch, (k, v) -> (v == null) ? 1 : ++v);
  }

  return result;
}

When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:

for (int i = 0; i < str.length(); i++) {
    int cp = str.codePointAt(i);
    String ch = String.valueOf(Character.toChars(cp));
    if(Character.charCount(cp) == 2) { // 2 means a surrogate pair
      i++;
    }
}

Any command-line input or output is written as follows:

$ mkdir css
$ cd css

Bold: Indicates a new term, an important word, or words that you see onscreen. For example, words in menus or dialog boxes appear in the text like this. Here is an example: "In Java, the logical AND operator is represented as &&, the logical OR operator is represented as ||, and the logical XOR operator is represented as ^."