Package java.util
Contains the collections framework, some internationalization support classes, a service loader, properties, random number generation, string parsing and scanning classes, base64 encoding and decoding, a bit array, and several miscellaneous utility classes. This package also contains legacy collection classes and legacy date and time classes.
Java Collections Framework
Provides classes for reading and writing the JAR (Java ARchive) file format, which is based on the standard ZIP file format with an optional manifest file.
This package allows applications to store and retrieve user and system preference and configuration data.
This package contains classes and interfaces that support a generic API for random number generation.
Classes to support functional-style operations on streams of elements, such as map-reduce transformations on collections.
This class provides a skeletal implementation of the Collection interface, to minimize the effort required to implement this interface.
This class provides a skeletal implementation of the List interface to minimize the effort required to implement this interface backed by a «random access» data store (such as an array).
This class provides a skeletal implementation of the Map interface, to minimize the effort required to implement this interface.
This class provides a skeletal implementation of the List interface to minimize the effort required to implement this interface backed by a «sequential access» data store (such as a linked list).
This class provides a skeletal implementation of the Set interface to minimize the effort required to implement this interface.
This class consists exclusively of static methods for obtaining encoders and decoders for the Base64 encoding scheme.
This class implements a decoder for decoding byte data using the Base64 encoding scheme as specified in RFC 4648 and RFC 2045.
This class implements an encoder for encoding byte data using the Base64 encoding scheme as specified in RFC 4648 and RFC 2045.
The Calendar class is an abstract class that provides methods for converting between a specific instant in time and a set of calendar fields such as YEAR , MONTH , DAY_OF_MONTH , HOUR , and so on, and for manipulating the calendar fields, such as getting the date of the next week.
This exception may be thrown by methods that have detected concurrent modification of an object when such modification is not permissible.
The Dictionary class is the abstract parent of any class, such as Hashtable , which maps keys to values.
An abstract wrapper class for an EventListener class which associates a set of additional parameters with the listener.
The Formattable interface must be implemented by any class that needs to perform custom formatting using the ‘s’ conversion specifier of Formatter .
FormattableFlags are passed to the Formattable.formatTo() method and modify the output format for Formattables.
GregorianCalendar is a concrete subclass of Calendar and provides the standard calendar system used by most of the world.
HexFormat converts between bytes and chars and hex-encoded strings which may include additional formatting markup such as prefixes, suffixes, and delimiters.
This class implements the Map interface with a hash table, using reference-equality in place of object-equality when comparing keys (and values).
Unchecked exception thrown when a character with an invalid Unicode code point as defined by Character.isValidCodePoint(int) is passed to the Formatter .
Unchecked exception thrown when the argument corresponding to the format specifier is of an incompatible type.
Unchecked exception thrown when a format string contains an illegal syntax or a format specifier that is incompatible with the given arguments.
Unchecked exception thrown when the precision is a negative value other than -1 , the conversion does not support a precision, or the value is otherwise unsupported.
Unchecked exception thrown when the format width is a negative value other than -1 or is otherwise unsupported.
Thrown by methods in Locale and Locale.Builder to indicate that an argument is not a well-formed BCP 47 tag.
Thrown by a Scanner to indicate that the token retrieved does not match the pattern for the expected type, or that the token is out of range for the expected type.
Thrown to indicate that an operation could not complete because the input did not conform to the appropriate XML document type for a collection of properties, as per the Properties specification.
An iterator for lists that allows the programmer to traverse the list in either direction, modify the list during iteration, and obtain the iterator’s current position in the list.
ListResourceBundle is an abstract subclass of ResourceBundle that manages resources for a locale in a convenient and easy to use list.
Unchecked exception thrown when there is a format specifier which does not have a corresponding argument or if an argument index refers to an argument that does not exist.
This class consists of static utility methods for operating on objects, or checking certain conditions before operation.
PropertyResourceBundle is a concrete subclass of ResourceBundle that manages resources for a locale using a set of static strings from a property file.
An instance of this class is used to generate a stream of pseudorandom numbers; its period is only 2 48 .
Marker interface used by List implementations to indicate that they support fast (generally constant time) random access.
ResourceBundle.Control defines a set of callback methods that are invoked by the ResourceBundle.getBundle factory methods during the bundle loading process.
SimpleTimeZone is a concrete subclass of TimeZone that represents a time zone for use with a Gregorian calendar.
Static classes and methods for operating on or creating instances of Spliterator and its primitive specializations Spliterator.OfInt , Spliterator.OfLong , and Spliterator.OfDouble .
A generator of uniform pseudorandom values (with period 2 64 ) applicable for use in (among other contexts) isolated parallel computations that may generate subtasks.
StringJoiner is used to construct a sequence of characters separated by a delimiter and optionally starting with a supplied prefix and ending with a supplied suffix.
The TooManyListenersException Exception is used as part of the Java Event model to annotate and implement a unicast special case of a multicast Event Source.
Report a bug or suggest an enhancement
For further API reference and developer documentation see the Java SE Documentation, which contains more detailed, developer-targeted descriptions with conceptual overviews, definitions of terms, workarounds, and working code examples. Other versions.
Java is a trademark or registered trademark of Oracle and/or its affiliates in the US and other countries.
Copyright © 1993, 2023, Oracle and/or its affiliates, 500 Oracle Parkway, Redwood Shores, CA 94065 USA.
All rights reserved. Use is subject to license terms and the documentation redistribution policy.
Create a Utility Class in Java
Utility classes in Java are also known as Helper Class. It is an efficient way to create methods that can be re-used. The code we need to use over and over again can be put inside a utility class.
Usage of Utility Class in Java
The Java utility class is a stateless class that cannot be instantiated and declared using final and public keywords. In the example given below, we have a UtilityClassExample , which has a private constructor that prevents instantiation. For example, there are many examples of Util classes in Java like Apache StringUtils , CollectionUtils , or java.lang.Math .
The methods in the utility class should be declared static and not abstract as object methods need instantiation. The final keyword prevents subclassing. Here, we create our own Utility class with a private constructor, which, when invoked, throws an exception. Since we declared a private constructor, default can not be created; hence class can not be instantiated.
In the code given below, we have all members of the UtilityClassExample static. If we need to add or subtract two int or float type variables, we created methods in the utility class to re-use the code. We also have a method that returns a number multiplied by ten.
In the method addFloatValues() , we have also used Math.round() to round off the result to the nearest int. The Float class has the sum() method that returns the sum of two float arguments. We call each member method of this utility class passing arguments and print the output in the main() method of the class TestUtitity . Thus this utility class has methods that are used very often.
public final class UtilityClassExample private static final int constantValue = 10; private UtilityClassExample() throw new java.lang.UnsupportedOperationException("Utility class and cannot be instantiated"); > public static int addIntValues(int i,int j) int sum = i + j; return sum; > public static int subIntValues(int i,int j) int diff = 0; if(i>j) diff = i - j; >else diff = j - i; > return diff; > public static float addFloatValues(float i, float j) float sum = Float.sum(i,j); return Math.round(sum); > public static float subFloatValues(float i, float j) float diff = 0.00f; if(i>j) diff = i - j; >else diff = j - i; > return diff; > public static int returnValAfterMultiplying(int i) return i * constantValue; > > class TestUtility public static void main(String [] args) int a = 4; int b = 9; int c = 7; float d = 3.12f; float e = 6.85f; System.out.println(+a+" multiplied by ten is : "+UtilityClassExample.returnValAfterMultiplying(a)); System.out.println(b+"+"+c+" is : "+UtilityClassExample.addIntValues(b,c)); System.out.println(d+"+"+e+" is : "+UtilityClassExample.addFloatValues(d,e)); System.out.println(b+"-"+a+" is : "+UtilityClassExample.subIntValues(b,a)); System.out.println(e+"-"+d+" is : "+UtilityClassExample.subFloatValues(e,d)); > > 4 multiplied by ten is : 40 9+7 is : 16 3.12+6.85 is : 10.0 9-4 is : 5 6.85-3.12 is : 3.73 It is not recommended to use a Utility class of your own as it reduces flexibility.
Rupam Saini is an android developer, who also works sometimes as a web developer., He likes to read books and write about various things.