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Java Tutorial

Java HOME Java Intro Java Get Started Java Syntax
Syntax Statements Code Challenge
Java Output
Print Text Print Numbers Code Challenge
Java Comments Java Variables
Variables Print Variables Multiple Variables Identifiers Constants (Final) Real-Life Examples Code Challenge
Java Data Types
Data Types Numbers Booleans Characters Real-Life Example Non-primitive Types The var Keyword Code Challenge
Java Type Casting Java Operators
Operators Arithmetic Assignment Comparison Logical Precedence Code Challenge
Java Strings
Strings Concatenation Numbers and Strings Special Characters StringBuilder Code Challenge
Java Math Java Booleans
Booleans Real-Life Example Code Challenge
Java If...Else
if else else if Short Hand If...Else Nested If Logical Operators Real-Life Examples Code Challenge
Java Switch
Switch Code Challenge
Java While Loop
While Loop Do/While Loop Real-Life Examples Code Challenge
Java For Loop
For Loop Nested Loops For-Each Loop Real-Life Examples Code Challenge
Java Break/Continue Java Arrays
Arrays Loop Through an Array Real-Life Examples Multidimensional Arrays Code Challenge

Java Methods

Java Methods Java Method Challenge Java Method Parameters
Parameters Return Values Code Challenge
Java Method Overloading Java Scope Java Recursion

Java Classes

Java OOP Java Classes/Objects Java Class Attributes Java Class Methods Java Class Challenge Java Constructors Java this Keyword Java Modifiers
Access Modifiers Non-Access Modifiers
Java Encapsulation Java Packages / API Java Inheritance Java Polymorphism Java super Keyword Java Inner Classes Java Abstraction Java Interface Java Anonymous Java OOP Visuals Java Enum
Enums Enum Constructor
Java User Input Java Date

Java Errors

Java Errors Java Debugging Java Exceptions Java Multiple Exceptions Java try-with-resources

Java Problem Solving

Java Problem Solving Java Build the Logic Java Test Cases

Java File Handling

Java Files Java Create Files Java Write Files Java Read Files Java Delete Files

Java I/O Streams

Java I/O Streams Java FileInputStream Java FileOutputStream Java BufferedReader Java BufferedWriter

Java Data Structures

Java Data Structures Java Collections Java List Java ArrayList Java LinkedList Java List Sorting Java Set Java HashSet Java TreeSet Java LinkedHashSet Java Map Java HashMap Java TreeMap Java LinkedHashMap Java Iterator Java Algorithms

Java Advanced

Java Wrapper Classes Java Generics Java Annotations Java RegEx Java Threads Java Lambda Java Optional Java Advanced Sorting

Java Projects

Java Projects

Java Cert

Java Certificate

Java How To's

Java How Tos
How Tos Add Two Numbers Swap Two Variables Even or Odd Number Reverse a Number Positive or Negative Square Root Area of Rectangle Celsius to Fahrenheit Sum of Digits Check Armstrong Num Random Number Count Words Count Vowels in a String Remove Vowels Count Digits in a String Reverse a String Palindrome Check Check Anagram Convert String to Array Remove Whitespace Count Character Frequency Sum of Array Elements Find Array Average Sort an Array Find Smallest Element Find Largest Element Second Largest Array Min and Max Array Merge Two Arrays Remove Duplicates Find Duplicates Shuffle an Array Factorial of a Number Fibonacci Sequence Find GCD Check Prime Number ArrayList Loop HashMap Loop Loop Through an Enum

Java Examples

Java Examples Java Videos Java Compiler Java Exercises Java Quiz Java Code Challenges Java Practice Problems Java Server Java Syllabus Java Study Plan Java Interview Q&A

Java Reference

Java Reference Java Keywords
assert abstract boolean break byte case catch char class continue const default do double else enum exports extends final finally float for goto if implements import instanceof int interface long module native new package private protected public return requires short static strictfp super switch synchronized this throw throws transient try var void volatile while
ArrayList Methods
add() addAll() clear() clone() contains ensureCapacity() forEach() get() indexOf() isEmpty() iterator() lastIndexOf() listIterator() remove() removeAll() removeIf() replaceAll() retainAll() set() size() sort() spliterator() subList() toArray() trimToSize()
Arrays Methods
compare() copyOf() deepEquals() equals() sort() fill() mismatch() length
BufferedReader
close() mark() markSupported() read() readLine() ready() reset() skip() lines() transferTo()
BufferedWriter
close() flush() newLine() write() append()
Character Methods
compare() getNumericValue() isAlphabetic() isDigit() isLetter() isLetterOrDigit() isLowerCase() isUpperCase() isWhitespace() toLowerCase() toString() toUpperCase() valueOf()
Collections Methods
sort() binarySearch() reverse() reverseOrder() shuffle() swap() frequency() max() min() disjoint() copy() fill() replaceAll() unmodifiableList() unmodifiableSet() unmodifiableMap()
Comparator Methods
compare() comparing() comparingInt() naturalOrder() reversed() reverseOrder() thenComparing() compareTo()
Date and Time
now() of() parse() getYear() getMonthValue() getMonth() getDayOfMonth() getDayOfWeek() plusDays() minusDays() plusMonths() plusYears() isBefore() isAfter() isLeapYear() lengthOfMonth() format() now() of() getHour() getMinute() plusHours() plusMinutes() now() of() toLocalDate() toLocalTime() format() ofPattern() format()
Enum Methods
compareTo() name() ordinal() toString() valueOf() values()
Errors & Exceptions
ArithmeticException ArrayIndexOutOfBoundsException ClassFormatError ClassNotFoundException ConcurrentModificationException FileNotFoundException IncompatibleClassChangeError InputMismatchException InterruptedException InvalidClassException IOException NegativeArraySizeException NoClassDefFoundError NoSuchFieldException NoSuchMethodException NullPointerException NumberFormatException RuntimeException StringIndexOutOfBoundsException TypeNotPresentException IllegalArgumentException IllegalStateException
File Methods
createNewFile() delete() exists() canRead() canWrite() isFile() isDirectory() length() getName() getAbsolutePath() getPath() getParent() list() listFiles() mkdir() mkdirs() renameTo() setReadOnly() setWritable() setReadable() setExecutable() canExecute()
FileInputStream
available() close() read() skip() getFD() getChannel()
FileOutputStream
close() flush() write() getFD() getChannel()
FileReader
read() ready() skip() close() mark() reset() markSupported() getEncoding() transferTo()
FileWriter
write() append() flush() close() getEncoding()
HashMap Methods
clear() clone() compute() computeIfAbsent() computeIfPresent() containsKey() containsValue() entrySet() forEach() get() getOrDefault() isEmpty() keySet() merge() put() putAll() putIfAbsent() remove() replace() replaceAll() size() values()
HashSet Methods
add() addAll() clear() clone() contains() isEmpty() iterator() remove() removeAll() size() spliterator() toArray()
Integer Methods
compare() compareTo() equals() intValue() max() min() parseInt() sum() toBinaryString() toHexString() toOctalString() toString() valueOf() MAX_VALUE MIN_VALUE
Iterator Methods
hasNext() next() remove()
LinkedHashMap Methods
clear() clone() compute() computeIfAbsent() computeIfPresent() containsKey() containsValue() entrySet() forEach() get() getOrDefault() isEmpty() keySet() merge() put() putAll() putIfAbsent() remove() replace() replaceAll() size() values()
LinkedHashSet Methods
add() addAll() clear() clone() contains() isEmpty() iterator() remove() removeAll() size() spliterator() toArray()
LinkedList Methods
add() addAll() addFirst() addLast() clear() clone() contains descendingIterator() element() forEach() get() getFirst() getLast() indexOf() isEmpty() iterator() lastIndexOf() listIterator() offer() offerFirst() offerLast() peek() peekFirst() peekLast() poll() pollFirst() pollLast() pop() push() remove() removeAll() removeFirst() removeFirstOccurrence() removeIf() removeLast() removeLastOccurrence() replaceAll() retainAll() set() size() sort() spliterator() subList() toArray()
Math Methods
abs() acos() addExact() asin() atan() atan2() cbrt() ceil() copySign() cos() cosh() decrementExact() exp() expm1() floor() floorDiv() floorMod() getExponent() hypot() IEEEremainder() incrementExact() log() log10() log1p() max() min() multiplyExact() negateExact() nextAfter() nextDown() nextUp() pow() random() rint() round() scalb() signum() sin() sinh() sqrt() subtractExact() tan() tanh() toDegrees() toIntExact() toRadians() ulp()
Optional Methods
empty() filter() flatMap() get() ifPresent() isPresent() map() of() ofNullable() orElse() orElseGet() orElseThrow()
Output Methods
print() printf() println()
Random Methods
ints() nextBoolean() nextDouble() nextFloat() nextGaussian() nextInt() nextLong() setSeed()
RegEx Methods
compile() flags() matcher() matches() pattern() quote() split() end() find() group() groupCount() lookingAt() matches() replaceAll() replaceFirst() reset() start()
Scanner Methods
close() delimiter() findInLine() findWithinHorizon() hasNext() hasNextBoolean() hasNextByte() hasNextDouble() hasNextFloat() hasNextInt() hasNextLine() hasNextLong() hasNextShort() locale() next() nextBoolean() nextByte() nextDouble() nextFloat() nextInt() nextLine() nextLong() nextShort() radix() reset() useDelimiter() useLocale() useRadix()
String Methods
charAt() codePointAt() codePointBefore() codePointCount() compareTo() compareToIgnoreCase() concat() contains() contentEquals() copyValueOf() endsWith() equals() equalsIgnoreCase() format() getBytes() getChars() hashCode() indexOf() intern() isEmpty() join() lastIndexOf() length() matches() offsetByCodePoints() regionMatches() replace() replaceAll() replaceFirst() split() startsWith() subSequence() substring() toCharArray() toLowerCase() toString() toUpperCase() trim() valueOf()
StringBuilder Methods
append() appendCodePoint() capacity() charAt() codePointAt() codePointBefore() codePointCount() delete() deleteCharAt() ensureCapacity() getChars() indexOf() insert() lastIndexOf() length() offsetByCodePoints() replace() reverse() setCharAt() setLength() subSequence() substring() toString() trimToSize()
System Methods
currentTimeMillis() nanoTime() exit() gc() getProperty() getProperties() setProperty() clearProperty() arraycopy() identityHashCode() lineSeparator() getenv() in out err
Thread Methods
currentThread() getName() getPriority() interrupt() isAlive() isInterrupted() join() run() setName() setPriority() sleep() start()
TreeMap Methods
firstKey() lastKey() firstEntry() lastEntry() floorKey() ceilingKey() lowerKey() higherKey() headMap() tailMap() subMap() pollFirstEntry() pollLastEntry() descendingMap() clear() clone() compute() computeIfAbsent() computeIfPresent() containsKey() containsValue() entrySet() forEach() get() getOrDefault() isEmpty() keySet() merge() put() putAll() putIfAbsent() remove() replace() replaceAll() size() values()
TreeSet Methods
first() last() floor() ceiling() lower() higher() headSet() tailSet() subSet() pollFirst() pollLast() descendingSet() add() addAll() clear() clone() contains() isEmpty() iterator() remove() removeAll() size() spliterator() toArray()



Java OOP Visuals

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The Four Main Ideas of OOP

In the previous chapters, you learned the four main ideas of object-oriented programming (OOP): encapsulation, inheritance, polymorphism and abstraction.

This page shows all four ideas in pictures, with the same Animal, Pig and Dog classes. Each object is drawn as a box, with its data and its methods inside.

Visualize OOP

Choose an idea below, and click "Next step" to see how it works:

Summary

  • Encapsulation: keep data private, and change it only through public methods. See Java Encapsulation.
  • Inheritance: a child class gets the attributes and methods of its parent class. See Java Inheritance.
  • Polymorphism: the same method call does different things, depending on the object. See Java Polymorphism.
  • Abstraction: hide the details, and show only what is important. See Java Abstraction.

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