Introduction to java.util

The java.util library is a core part of the Java Standard Library. It provides a wide range of utility classes that make everyday programming tasks easier and more efficient. You will use java.util in almost every Java project, especially when you need to manage data, work with dates and times, or use helpful tools for common programming patterns.

Here are some of the most important features of the java.util package:

• Collections Framework: Includes data structures like ArrayList, HashMap, HashSet, and LinkedList; helps you store, organize, and manipulate groups of objects efficiently.
• Date and Time Classes: Offers tools such as Date, Calendar, and TimeZone to handle dates, times, and time zones; useful for scheduling, logging, or tracking events.
• Helper Classes: Includes utilities like Random for generating random numbers, Scanner for reading user input, and Objects for working safely with object references.
• Other Utilities: Provides classes for tasks like working with properties files (Properties), observing changes (Observable), and managing tasks (Timer).

By learning how to use java.util, you will be able to solve many programming problems more easily and write cleaner, more reliable code.

Key Components in java.util

The java.util package provides essential classes and methods to help you manage data, perform operations on collections, and work with dates. Here are the most important components you will use:

ArrayList

• Stores a dynamic list of elements that can grow or shrink as needed;
• Allows you to add, remove, or access elements by their index;
• Maintains the order in which you add elements.

Example:

ArrayList<String> names = new ArrayList<>();
names.add("Alice");
names.add("Bob");
System.out.println(names.get(0)); // prints "Alice"

HashMap

• Stores key-value pairs so you can quickly look up a value by its key;
• Does not maintain any specific order of keys;
• Keys must be unique, but values can repeat.

Example:

HashMap<String, Integer> scores = new HashMap<>();
scores.put("Alice", 90);
scores.put("Bob", 85);
System.out.println(scores.get("Alice")); // prints 90

Date

• Represents a specific moment in time, with millisecond precision;
• Useful for storing and comparing dates and times;
• Often used with other date and time utilities.

Example:

Date now = new Date();
System.out.println(now); // prints the current date and time

Collections Utility Methods

• The Collections class provides static methods to work with collections such as lists and sets;
• Includes methods to sort, shuffle, reverse, and search collections;
• Makes common operations simpler and less error-prone.

Example:

ArrayList<Integer> numbers = new ArrayList<>();
numbers.add(3);
numbers.add(1);
numbers.add(2);
Collections.sort(numbers);
System.out.println(numbers); // prints [1, 2, 3]

These components form the foundation for working with data in Java applications. You will use them frequently to organize, store, and process information efficiently.