500+ Guides on Java Top Classes and Methods

This page contains productive guides on important core Java built-in classes and their methods with examples.

Newly Added Java API Guides

• Java Optional Class Methods/APIs Guide
• Java 8 Collectors Class API Guide
• Java Stream Intermediate Operations API Guide
• Java Stream Terminal Operations API Guide
• Java 8 StringJoiner Class API Guide

java.lang Package API/Methods Guides

java.lang  - java.lang package provides classes that are fundamental to the design of the Java programming language.

• java.lang Object Class API Guide 
• java.lang java.lang StringBuilder Class API Guide 
• java.lang StringBuffer Class API Guide
• java.lang Thread Class API Guide
• java.lang Boolean Class API Guide
• java.lang Byte Class API Guide
• java.lang Character Class API Guide
• java.lang Double Class API Guide 
• java.lang Float Class API Guide
• java.lang Long Class API Guide
• java.lang Integer Class API Guide
• java.lang Short Class API Guide
• java.lang Enum Class API Guide
• java.lang ThreadLocal Class API Guide
• java.lang Package Class API Guide
• java.lang Number Class API Guide
• java.lang ThreadGroup Class API Guide
• java.lang Throwable Class API Guide 
• java.lang Comparable Interface API Guide
• java.lang.reflect Array Class API Guide 
• java.lang.reflect.Field Class API Guide 
• java.lang.reflect.Constructor Class API Guide

java.util Package API/Methods Guides

java.util - java.util package contains the collections framework, legacy collection classes, event model, date and time facilities, internationalization, and miscellaneous utility classes.

• java.util ArrayList Class API Guide 
• java.util.Arrays Class API Guide 
• java.util.Collections Class API Guide 
• java.util EnumMap Class API Guide 
• java.util EnumSet Class API Guide 
• java.util HashMap Class API Guide 
• java.util HashSet Class API Guide 
• java.util IdentityHashMap Class API Guide 
• java.util LinkedHashMap Class API Guide
• java.util LinkedHashSet Class API Guide 
• java.util LinkedList Class API Guide 
• java.util TreeMap Class API Guide 
• java.util TreeSet Class API Guide 
• java.util WeakHashMap Class API Guide 
• java.util Comparator Interface API Guide
• Java Optional Class Methods/APIs Guide

java.util.concurrent Package API/Methods Guides

java.util.concurrent  -The java.util.concurrent package provides utility classes that are commonly useful in concurrent programming.

• java.util.concurrent.ExecutorService Interface API Guide
• java.util.concurrent.ScheduledExecutorService interface API Guide 
• java.util.concurrent.Executors Class API Guide 
• java.util.concurrent.Callable and Future API Guide 
• java.util.concurrent.CopyOnWriteArrayList Class API
• Guide java.util.concurrent.CopyOnWriteArraySet Class API Guide

java.io Package API/Methods Guides

java.io - Java.io package provides classes for system input and output through data streams, serialization, and the file system.

• java.io FileOutputStream Class API Guide 
• java.io FileInputStream Class API Guide 
• java.io ByteArrayOutputStream Class API Guide 
• java.io ByteArrayInputStream Class API Guide 
• java.io BufferedWriter Class API Guide 
• java.io BufferedReader Class API Guide 
• java.io BufferedOutputStream Class API Guide 
• java.io BufferedInputStream Class API Guide 
• java.io FileWriter Class API Guide 
• java.io FileReader Class API Guide 
• java.io DataOutStream Class API Guide
• java.io DataInputStream Class API Guide 
• java.io ObjectOutputStream Class API Guide 
• java.io ObjectInputStream Class API Guide

java.time Package API/Methods Guides

java.time - Java 8 has introduced a new Date and Time API under java.time package. The java.time package provides API for dates, times, instants, and durations.

• Java 8 - Clock Class API Guide 
• Java 8 - Period Class API Guide 
• Java 8 - Year Class API Guide
• Java 8 - LocalTime Class API Guide 
• Java 8 - LocalDate Class API Guide 
• Java 8 - LocalDateTime Class API Guide
• Java 8 - ZonedDateTime Class API Guide 
• Java 8 - Duration Class API Guide 
• Java 8 - Instant Class API Guide 
• Java 8 - DayOfWeek Enum API Guide 
• Java 8 - Month Enum API Guide 
• Java Date Time API Guide

java.sql Package API/Methods Guides 

java.sql - The java.sql package provides the API for accessing and processing data stored in a data source (usually a relational database) using the Java programming language.

• JDBC Connection Interface API Guide 
• JDBC Statement Interface API Guide 
• JDBC PreparedStatement Interface API Guide 
• JDBC CallableStatement Interface API Guide 
• JDBC ResultSet Interface API Guide 
• JDBC ResultSetMetaData Interface API Guide 
• JDBC DatabaseMetaData Interface
• JDBC DriverManager Class API Guide

java.lang.reflect Package API/Methods Guides 

java.lang.reflect - java.lang.reflect package provides classes and interfaces that are used to obtain reflective information about classes and objects.

• java.lang.reflect.Array Class API Guide 
• java.lang.reflect.Method Class API Guide 
• java.lang.reflect.Field Class API Guide
• java.lang.reflect.Constructor Class API Guide

java.math Package API/Methods Guides 

java.math - java.math package provides classes for performing arbitrary-precision integer arithmetic (BigInteger) and arbitrary-precision decimal arithmetic (BigDecimal).

• java.math BigDecimal Class API Guide
• java.math BigInteger Class API Guide 
• java.math MathContext Class API Guide

java.nio.file Package API/Methods Guides 

java.nio.file - java.nio.file package defines interfaces and classes for the Java virtual machine to access files, file attributes, and file systems.

• Java NIO Files Class API Guide

java.util.function Package API/Methods Guides

Functional interfaces provide target types for lambda expressions and method references.

• Java 8 Function Interface Example
• Java 8 Predicate interface Example
• Java 8 Consumer Interface Example
• Java 8 Supplier Interface Example
• Java 8 BiFunction Example
• Java 8 BiConsumer Example
• Java 8 BiPredicate Example

Guides on Java Methods

Java String Class Methods:

Java String charAt() example
Java String concat() example
Java String contains() example
Java String endsWith() example
Java String equals() example
Java String equalsIgnoreCase() example
Java String getBytes() example
Java String indexOf() example
Java String isEmpty() example
Java String lastIndexOf() example
Java String length() example
Java String replace() example
Java String split() example
Java String startsWith() example
Java String substring() example
Java String toLowerCase() example
Java String toUpperCase() example
Java String trim() example
Java String valueOf() example

Java String isBlank()
Java String lines()
Java String strip()
Java String stripLeading()
Java String stripTrailing()
Java String indent()
Java String transform()

Java CharSequence stripIndent()

Java Map Interface Methods:

Java Map put() example
Java Map get() example
Java Map remove() example
Java Map containsKey() example

Java Map keySet() example
Java Map values() example
Java Map entrySet() example

Map containsValue() example

Java Map copyOf()

Java Set Interface Methods:

Java Set add() example
Java Set contains() example
Java Set isEmpty() example
Java Set remove() example
Java Set size() example Java

Java Set copyOf()

Java List Interface Methods:

Java List add() example
Java List clear() example
Java List contains() example
Java List get() example
Java List indexOf() example
Java List remove() example
Java List size() example
Java List toArray() example

Java List copyOf()

Java Collections Utility Class Methods:

Java Collections min()
Java Collections max()
Java Collections binarySearch()
Java Collections frequency()

Java Math Class Methods:

Java Math abs() example
Java Math ceil() example
Java Math floor() example
Java Math max() example
Java Math pow() example
Java Math sqrt() example
Java Math random() example Java Path get()

Java Path Class Methods:

Java Path getParent()
Java Path resolve()

Java Path get()

Java Files Class Methods:

Java Files copy()
Java Files delete()
Java Files exists()
Java Files move()
Java Files newBufferedReader()
Java Files newBufferedWriter()
Java Files readAllBytes()

Java Files writeString()
Java Files readString()
Java Files isSameFile()
Java Files mismatch()

Java File Class Methods:

Java File mkdir()

Java File list()

Java File getAbsolutePath()

Java File exists()

Java File exists()

Java File delete()

Java File createNewFile()

Java Arrays Class Methods:

Java Arrays asList()
Java Arrays sort()
Java Arrays deepToString()
Java Arrays toString()

Java Calendar and Date Class Methods:

Java Date getTime()

Java Calendar getInstance()

Java Calendar setTime()

Java Locale getDisplayName()

Java Calendar getTime()

Java Scanner Methods:

Java Scanner nextLine()

Java Scanner nextDouble()

Java Scanner hasNext()

Java Scanner useDelimiter()

Java System Methods:

Java System gc()

Java System currentTimeMillis()

Java System arraycopy()

Java Character Class Methods:

Java Character toUpperCase()

Java Character toLowerCase()

Java Character isWhitespace()

Java Character isLetter()

Java Character isDigit()

Java Double Class Methods:

Java Double valueOf()

Java Double toString()

Java Double parseDouble()

Java Integer Class Methods:

Java Integer valueOf()

Java Integer toString()

Java Integer parseInt()

Java Stack and Queue Class Methods:

Java Stack search()

Java Stack peek()

Java Stack pop()

Java Stack push()

Java Queue peek()

Java Queue poll()

Java Queue offer()

Java Thread Class Methods:

Java Thread currentThread()
Java Thread start()
Java Thread join()
Java Thread sleep()
Java Thread yield()
Java Thread interrupt()
Java Thread isAlive()

Java Runnable Interface Methods:

Java Runtime freeMemory()
Java Runtime totalMemory()
Java Runtime.exec()

Java Predicate Interface Methods:

Java Predicate test()
Java Predicate and()
Java Predicate or()

Java Function Interface Methods:

Java Function apply()
Java Function compose()
Java Function identity()

Java Consumer Interface Methods:

Java Consumer accept()
Java Consumer andThen()

Java Stream Methods:

Java Stream filter()
Java Stream map()
Java Stream collect()
Java Stream forEach()
Java Stream count()
Java Stream sorted()
Java Stream findFirst()
Java Stream anyMatch()
Java Stream allMatch()
Java Stream noneMatch()
Java Stream toArray()
Java Stream concat()
Java Stream parallel()

Java Stream takeWhile()
Java Stream dropWhile()
Java Stream ofNullable()
Java Stream iterate()

Java LocalDateTime Class Methods:

Java LocalDateTime now()
Java LocalDateTime of()
Java LocalDateTime plusDays()
Java LocalDateTime minusHours()

Java Duration Class Methods:

Java Duration between()
Java Duration plus()
Java Duration minus()
Java Duration toHours()
Java Duration toMinutes()

Java Period Class Methods:

Java Period getDays()
Java Period getMonths()
Java Period getYears()

Java LocalDate Class Methods:

Java LocalDate now()
Java LocalDate of()
Java LocalDate plusDays()
Java LocalDate minusDays()
Java LocalDate getDayOfYear()

Java LocalTime Class Methods:

Java LocalTime now()
Java LocalTime of()
Java LocalTime plusHours()
Java LocalTime minusMinutes()
Java LocalTime getHour()

Java ZonedDate Class Methods:

Java ZonedDateTime now()
Java ZonedDateTime of()
Java ZonedDateTime plusDays()
Java ZonedDateTime minusWeeks()
Java ZonedDateTime getZone()

Java Instant Class Methods:

Java Instant now()
Java Instant ofEpochMilli()
Java Instant plusSeconds()
Java Instant minusSeconds()

Java Currency Class Methods:

Java Currency getInstance()

Java UUID Class Methods:

Java UUID randomUUID()
Java UUID fromString()

Java Timestamp Class Methods:

Java Timestamp valueOf()
Java Timestamp getTime()

Java SQLDate and SQLTime Class Methods:

Java SQLDate valueOf()
Java SQLTime valueOf()

Java ResultSet Class Methods:

Java ResultSet getString()
Java ResultSet getInt()
Java ResultSet next()

Java PreparedStatement Interface Methods:

Java PreparedStatement setString()
Java PreparedStatement executeQuery()

Java DriverManger Class Methods:

Java DriverManager getConnection()

Java Connection Interface Methods:

Java Connection prepareStatement()
Java Connection commit()
Java Connection rollback()

Java Statement Interface Methods:

Java Statement executeQuery()
Java Statement executeUpdate()

Java Clob and Blob Class Methods:

Java Clob getSubString()
Java Blob getBytes()

Java ArrayDeque Class Methods:

Java ArrayDeque poll()
Java ArrayDeque push()
Java ArrayDeque pop()

Java HashSet and LinkedHashSet Class Methods:

Java HashSet clone()
Java LinkedHashSet contains()

Java HashMap and TreeMap Class Methods:

Java HashMap putIfAbsent()
Java HashMap replace()
Java TreeMap firstKey()

Java LinkedList Class Methods:

Java LinkedList addFirst()
Java LinkedList addLast()
Java LinkedList removeFirst()

Java Properties Class Methods

Java Properties load()
Java Properties store()
Java Properties getProperty()
Java Properties setProperty()

Java SecureRandom Class Methods

Java SecureRandom nextInt()
Java SecureRandom nextBytes()

Java MessageDigest Class Methods

Java MessageDigest getInstance()

Java Base64 Class Methods

Java Base64 getEncoder()
Java Base64 getDecoder()

Java Cipher Class Methods

Java Cipher getInstance()
Java Cipher doFinal()

Java KeyPairGenerator Class Methods

Java KeyPairGenerator getInstance()
Java KeyPairGenerator generateKeyPair()

Java Signature Class Methods

Java Signature getInstance()
Java Signature initSign()
Java Signature verify()

Java Optional Class Methods

Java Optional stream()
Java Optional ifPresentOrElse()
Java Optional or()

Java Pattern Class Methods

Java Pattern asMatchPredicate()