java.util Package in Java

Learn via video course
FREE
View all courses
Java Course - Mastering the Fundamentals
Java Course - Mastering the Fundamentals
by Tarun Luthra
1000
5
Start Learning
Java Course - Mastering the Fundamentals
Java Course - Mastering the Fundamentals
by Tarun Luthra
1000
5
Start Learning

Overview

The java.util package in Java is a built-in package that contains various utility classes and interfaces. It provides basic functionality for commonly occurring use cases. It contains Java's collections framework, date and time utilities, string-tokenizer, event-model utilities, etc.

Introduction to java.util Package in Java

To support the needs of a software developer, Java provides various built-in and pre-written functionalities in the form of packages. These built-in packages contain various kinds of classes and interfaces that can be used to develop better and maintainable code. Some of the built-in Java packages are shown in the figure given below:

Package in Java

One of the most important Java packages is the java.util package. The java.util package contains several pre-written classes that can act as a base to solve commonly occurring problems in software development. It provides basic and essential source code snippets to the programmers that can lead to clean and maintainable code. It contains various classes and methods that perform common tasks such as string tokenization, date and time formatting, Java Collections implementation, etc.

What does import java.util do in Java?

To load the basic utility classes and interfaces provided by the java.util package, we need to use Java's import keyword. The import keyword is used to access and load the package and its respective classes into the Java program. The syntax to import the package or its classes is given below:

Here, the first import statement is used to load a certain class from the specified package, whereas the second statement is used to import the whole package into the Java program. For the java.util package:

The above statement is used to load all the functionalities provided by the java.util package.

java.util Package Import Statement Example

Let's look at some examples to understand the use of import statements while loading the java.util package:

Example 1: To Load the Whole Util Package

As discussed, this statement will load all the pre-written classes and interfaces provided by the java.util package.

Example 2: To Load a Specific Class from the java.util Package

The above statement is importing the Scanner class available in the java.util package. This class is widely used to take input from the user in a Java program.

What is the Use of java.util Package in Java?

The java.util package in Java consists of several components that provide basic necessities to the programmer. These components include:

Components of Java Util Package

Let's explore these components and their usage in Java:

  • Data Structure Classes: The java.util package contains several pre-written data structures like Dictionary, Stack, LinkedList, etc. that can be used directly in the program using the import statements.
  • Date and Time Facility: The java.util package provides several date and time-related classes that can be used to create and manipulate date and time values in a program.
  • Enumeration: It provides a special interface known as enumeration(enum for short) that can be used to iterate through a set of values.
  • Exceptions: It provides classes to handle commonly occurring exceptions in a Java program.
  • Miscellaneous Utility Classes: The java.util package contains essential utilities such as the string tokenizer and random-number generator.

What is Collections Framework in Java?

Collections Framework in Java is a special part of the java.util package that can be used to represent and manipulate collections. It provides easy storage and organization of a group of objects (or collection). It includes pre-written classes, interfaces, and algorithms under a unified architecture.

java.util Package Interfaces

InterfaceDescription
CollectionsRoot interface for the Collections API
ComparatorProvides sorting logic
DequeImplements Deque data structure
EnumerationProduces enumeration objects
IteratorProvides iteration logic
ListImplements an ordered collection (Sequence)
MapImplements Map data structure (key-value pairs)
QueueImplements Queue data structure
SetProduces a collection that contains no duplicate elements
SortedSetProduces a set that remembers the total ordering

java.util Package Classes

ClassDescription
CollectionsProvides methods to represent and manage collections
FormatterAn interpreter for format strings
ScannerText scanner used to take user inputs
ArraysProvides methods for array manipulation
LinkedListImplements Doubly-linked list data structure
HashMapImplements Map data structure using Hash tables
TreeMapImplements Red-Black tree data structure
StackImplements last-in-first-out (LIFO) data structure
PriorityQueueImplements unbounded priority queue data structure
DateRepresents a specific instance of time
CalendarProvides methods to manipulate calendar fields
RandomUsed to generate a stream of pseudorandom numbers.
StringTokenizerUsed to break a string into tokens
Timer, TimerTaskUsed by threads to schedule tasks
UUIDRepresents an immutable universally unique identifier

java.util Package Enum

Enum ClassDescription
Formatter.BigDecimalLayoutFormUsed for BigDecimal formatting
Locale.CategoryUsed for locale categories
Locale.FilteringModeProvides constants for filtering mode selection
Locale.IsoCountryCodeUsed to specify the type defined in ISO 3166

java.util Package Exceptions

Exception ClassDescription
ConcurrentModificationExceptionWhen an object is modified concurrently without permission
EmptyStackExceptionIndicates that the Stack is empty
InputMismatchExceptionWhen the user does not provide valid input
MissingResourceExceptionIndicates absence of a resource
NoSuchElementExceptionIndicates absence of requested element
PatternSyntaxExceptionIndicates syntax error in a regular-expression pattern
IllegalFormatExceptionIndicates that a format string contains illegal syntax

Conclusion

  • Util package in Java is a built-in package that contains several pre-written utility classes and interfaces.
  • The import java.util.*; statement can be used to load the contents of the java.util package in a Java program.
  • It consists of components such as data structures, exceptions, enumerations, utility classes, etc.
  • It allows us to write clean and maintainable code.
  • It contains the Collections Framework which is used to represent and manipulate collections.