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Introduction to java.util

The java.util package is arguably the most extensively used package in the Java ecosystem (after java.lang). It provides a massive collection of utility classes and interfaces that solve common programming problems, primarily focused on Data Structures and Algorithms.

While the java.lang package is imported automatically, you must explicitly import classes from the java.util package using the import statement.

What is in the java.util package?​

The java.util package is famous for housing the Java Collections Framework, which is the backbone of data manipulation in Java. It also contains several incredibly powerful auxiliary utility classes.

Here is an overview of what we will cover in this module:

1. The Collections Framework​

The Collections Framework provides a unified architecture for storing and manipulating groups of objects. It includes:

  • Interfaces: List, Set, Queue, Map.
  • Classes: ArrayList, LinkedList, HashSet, TreeSet, HashMap, PriorityQueue, etc.
  • Algorithms: The Collections utility class for sorting and searching.

2. The Scanner Class​

The Scanner class is used to easily read input from various sources, such as user input from the console (System.in) or from files.

3. Date & Time Facilities​

Legacy classes for handling dates and times, primarily Date and Calendar (though modern Java development prefers the java.time package introduced in Java 8).

4. Auxiliary Utility Classes​

Beyond collections, the java.util package contains auxiliary classes that handle specific tasks:

  • Random: For generating pseudo-random numbers.
  • UUID: For generating Universally Unique Identifiers.
  • StringTokenizer: A legacy class for breaking strings into tokens.
  • Properties: For reading and writing configuration files.
  • Timer & TimerTask: For scheduling tasks to execute in the background.

Let's dive into the core of this package—the Collections Framework—in the next section!