%5C%0A**Java**%20is%20one%20of%20the%20most%20popular%20programming%20language%20in%20the%20world.%20Java%20first%20appeared%2027%20years%20ago%20and%20was%20designed%20by%20James%20Gosling.%0A%0A%5C%0AJava%20is%20a%20high%20level%2C%20object%20oriented%20programming%20language.%20In%20this%20course%20you%20will%20learn%20the%20fundamentals%20of%20Java%20programming%20language.%20After%20completing%20this%20course%2C%20I%20hope%20you%20will%20have%20a%20solid%20understanding%20of%20Java%20eco-system.%20Along%20with%20Java%20fundamentals%20I%20will%20also%20try%20to%20cover%20some%20topics%20from%20latest%20Java%20versions%20such%20as%20Stream%20API%2C%20New%20IO%20API%20etc.%0A%0A%5C%0A**Language**%3A%20English%0A%0A%5C%0A**Level**%3A%20Intermediate%0A%0A%5C%0A**Content%20Format**%3A%20Text%0A%0A%5C%0A**Note%3A%20Use%20nagivation%20bar%20to%20browse%20course%20materials.**

%60%60%60java%0Apublic%20class%20LearnYouSomeJavaForGreatGood%20%7B%0A%0A%20%20%20%20public%20static%20void%20main(String%5B%5D%20args)%20%7B%0A%20%20%20%20%20%20%20%20System.out.println(%22Hello%20World%22)%3B%0A%20%20%20%20%7D%0A%7D%0A%60%60%60

Hello World

%23%23%23%20Data%20Types%20in%20Java%0A%0AA%20data%20type%20is%20a%20classification%20that%20specifies%20the%20kind%20of%20value%20that%20a%20variable%20can%20hold.%20In%20Java%2C%20there%20are%20two%20types%20of%20data%3A%20primitive%20and%20reference.%0A%0A%23%23%23%23%20Primitive%20Data%20Types%0A%0APrimitive%20data%20types%20are%20the%20basic%20data%20types%20that%20are%20built%20into%20the%20Java%20language.%20They%20include%3A%0A%0A*%20boolean%3A%20a%20value%20that%20is%20either%20true%20or%20false%0A*%20char%3A%20a%20single%20character%0A*%20byte%3A%20an%208-bit%20integer%0A*%20short%3A%20a%2016-bit%20integer%0A*%20int%3A%20a%2032-bit%20integer%0A*%20long%3A%20a%2064-bit%20integer%0A*%20float%3A%20a%2032-bit%20floating%20point%20number%0A*%20double%3A%20a%2064-bit%20floating%20point%20number%0A%0APrimitive%20data%20types%20are%20stored%20directly%20in%20the%20memory%20and%20are%20generally%20more%20efficient%20than%20reference%20data%20types.%20However%2C%20they%20are%20limited%20in%20the%20kind%20of%20information%20they%20can%20represent.%0A%0A%23%23%23%23%20Reference%20Data%20Types%0A%0AReference%20data%20types%20are%20variables%20that%20hold%20a%20reference%20(i.e.%2C%20an%20address)%20to%20an%20object%20in%20memory.%20This%20means%20that%20when%20you%20create%20an%20object%20in%20Java%2C%20you%20are%20actually%20creating%20a%20reference%20to%20the%20object.%0A%0ASome%20examples%20of%20reference%20data%20types%20in%20Java%20include%3A%0A%0A*%20String%3A%20a%20sequence%20of%20characters%0A*%20Array%3A%20an%20ordered%20collection%20of%20elements%0A*%20Classes%3A%20a%20template%20for%20creating%20objects%0A%0AReference%20data%20types%20are%20more%20flexible%20than%20primitive%20data%20types%20because%20they%20can%20represent%20a%20wide%20variety%20of%20information.%20However%2C%20they%20are%20less%20efficient%20because%20they%20require%20additional%20memory%20to%20store%20the%20reference%20to%20the%20object.%0A%0A%23%23%23%20Objects%20in%20Java%0A%0AAn%20object%20is%20a%20self-contained%20unit%20that%20consists%20of%20both%20data%20and%20behavior.%20In%20Java%2C%20objects%20are%20created%20from%20classes%2C%20which%20act%20as%20a%20template%20for%20creating%20objects.%0A%0ATo%20create%20an%20object%20in%20Java%2C%20you%20first%20need%20to%20define%20a%20class.%20A%20class%20is%20a%20blueprint%20that%20defines%20the%20properties%20and%20methods%20of%20an%20object.%20Here%20is%20an%20example%20of%20a%20simple%20class%20in%20Java%3A%0A%0A%60%60%60java%0Apublic%20class%20Person%20%7B%0A%20%20%2F%2F%20properties%0A%20%20private%20String%20name%3B%0A%20%20private%20int%20age%3B%0A%20%20%0A%20%20%2F%2F%20methods%0A%20%20public%20void%20setName(String%20name)%20%7B%0A%20%20%20%20this.name%20%3D%20name%3B%0A%20%20%7D%0A%20%20%0A%20%20public%20String%20getName()%20%7B%0A%20%20%20%20return%20this.name%3B%0A%20%20%7D%0A%20%20%0A%20%20public%20void%20setAge(int%20age)%20%7B%0A%20%20%20%20this.age%20%3D%20age%3B%0A%20%20%7D%0A%20%20%0A%20%20public%20int%20getAge()%20%7B%0A%20%20%20%20return%20this.age%3B%0A%20%20%7D%0A%7D%0A%60%60%60%0A%0ATo%20create%20an%20object%20from%20this%20class%2C%20you%20would%20use%20the%20%60new%60%20keyword%2C%20like%20this%3A%0A%0A%60%60%60java%0APerson%20person%20%3D%20new%20Person()%3B%0A%60%60%60%0A%0AThis%20creates%20an%20instance%20of%20the%20Person%20class%20and%20assigns%20it%20to%20the%20person%20variable.%20You%20can%20then%20use%20the%20methods%20of%20the%20Person%20class%20to%20set%20and%20get%20the%20values%20of%20the%20object's%20properties.%20For%20example%3A%0A%0A%60%60%60java%0Aperson.setName(%22John%22)%3B%0Aperson.setAge(30)%3B%0A%0ASystem.out.println(person.getName())%3B%20%2F%2F%20prints%20%22John%22%0ASystem.out.println(person.getAge())%3B%20%2F%2F%20prints%2030%0A%60%60%60

Data Types & Objects

%23%23%23%20Conditionals%20in%20Java%0A%0AConditionals%20are%20statements%20that%20allow%20you%20to%20execute%20different%20blocks%20of%20code%20based%20on%20whether%20a%20particular%20condition%20is%20true%20or%20false.%20In%20Java%2C%20you%20can%20use%20the%20if%20statement%20to%20execute%20a%20block%20of%20code%20if%20a%20condition%20is%20true%2C%20and%20the%20if-else%20statement%20to%20execute%20a%20block%20of%20code%20if%20the%20condition%20is%20true%20or%20another%20block%20of%20code%20if%20the%20condition%20is%20false.%0A%0AHere%20is%20an%20example%20of%20an%20if%20statement%20in%20Java%3A%0A%0A%60%60%60java%0Aint%20x%20%3D%2010%3B%0Aif%20(x%20%3E%205)%20%7B%0A%20%20System.out.println(%22x%20is%20greater%20than%205%22)%3B%0A%7D%0A%60%60%60%0A%0AThis%20code%20will%20print%20%22x%20is%20greater%20than%205%22%20because%20the%20condition%20x%20%3E%205%20is%20true.%0A%0AHere%20is%20an%20example%20of%20an%20if-else%20statement%20in%20Java%3A%0A%0A%60%60%60java%0Aint%20y%20%3D%203%3B%0Aif%20(y%20%3E%205)%20%7B%0A%20%20System.out.println(%22y%20is%20greater%20than%205%22)%3B%0A%7D%20else%20%7B%0A%20%20System.out.println(%22y%20is%20not%20greater%20than%205%22)%3B%0A%7D%0A%60%60%60%0A%0AThis%20code%20will%20print%20%22y%20is%20not%20greater%20than%205%22%20because%20the%20condition%20y%20%3E%205%20is%20false.%0A%0AIn%20addition%20to%20the%20if%20and%20if-else%20statements%2C%20Java%20also%20provides%20the%20switch%20statement%2C%20which%20allows%20you%20to%20execute%20different%20blocks%20of%20code%20based%20on%20the%20value%20of%20a%20variable.%20Here%20is%20an%20example%20of%20a%20switch%20statement%20in%20Java%3A%0A%0A%60%60%60java%0Aint%20z%20%3D%202%3B%0Aswitch%20(z)%20%7B%0A%20%20case%201%3A%0A%20%20%20%20System.out.println(%22z%20is%201%22)%3B%0A%20%20%20%20break%3B%0A%20%20case%202%3A%0A%20%20%20%20System.out.println(%22z%20is%202%22)%3B%0A%20%20%20%20break%3B%0A%20%20case%203%3A%0A%20%20%20%20System.out.println(%22z%20is%203%22)%3B%0A%20%20%20%20break%3B%0A%20%20default%3A%0A%20%20%20%20System.out.println(%22z%20is%20not%201%2C%202%2C%20or%203%22)%3B%0A%7D%0A%60%60%60%0A%0AThis%20code%20will%20print%20%22z%20is%202%22%20because%20the%20value%20of%20z%20is%202.%0A%0A%23%23%23%20Loops%20in%20Java%0A%0ALoops%20are%20statements%20that%20allow%20you%20to%20execute%20a%20block%20of%20code%20repeatedly%20until%20a%20certain%20condition%20is%20met.%20In%20Java%2C%20there%20are%20three%20types%20of%20loops%3A%20the%20for%20loop%2C%20the%20while%20loop%2C%20and%20the%20do-while%20loop.%0A%0A**The%20for%20Loop**%0AThe%20for%20loop%20is%20used%20to%20execute%20a%20block%20of%20code%20a%20specific%20number%20of%20times.%20Here%20is%20an%20example%20of%20a%20for%20loop%20in%20Java%3A%0A%0A%60%60%60java%0Afor%20(int%20i%20%3D%200%3B%20i%20%3C%205%3B%20i%2B%2B)%20%7B%0A%20%20System.out.println(%22Hello%2C%20World!%22)%3B%0A%7D%0A%60%60%60%0A%0AThis%20code%20will%20print%20%22Hello%2C%20World!%22%20five%20times.%20The%20loop%20initializes%20a%20variable%20i%20to%200%2C%20then%20checks%20if%20i%20is%20less%20than%205.%20If%20it%20is%2C%20it%20executes%20the%20block%20of%20code%20and%20increments%20i%20by%201.%20If%20i%20is%20not%20less%20than%205%2C%20the%20loop%20ends.%0A%0A**The%20while%20Loop**%0AThe%20while%20loop%20is%20used%20to%20execute%20a%20block%20of%20code%20as%20long%20as%20a%20certain%20condition%20is%20true.%20Here%20is%20an%20example%20of%20a%20while%20loop%20in%20Java%3A%0A%0A%60%60%60java%0Aint%20j%20%3D%200%3B%0Awhile%20(j%20%3C%205)%20%7B%0A%20%20System.out.println%0A%7D%0A%60%60%60

Conditions & Loops

Java%20methods%20are%20an%20essential%20concept%20in%20Java%20programming.%20A%20method%20is%20a%20block%20of%20code%20that%20performs%20a%20specific%20task%20and%20can%20be%20called%20from%20anywhere%20in%20a%20program.%20In%20this%20blog%20post%2C%20we%20will%20explore%20methods%20in%20more%20detail%20and%20see%20how%20they%20are%20used%20in%20Java%20programming.%0A%0A%23%23%23%20What%20are%20Java%20Methods%3F%0A%0AJava%20methods%20are%20a%20way%20to%20encapsulate%20a%20block%20of%20code%20and%20give%20it%20a%20name.%20This%20makes%20it%20easier%20to%20reuse%20the%20code%20in%20different%20parts%20of%20a%20program%20and%20makes%20the%20code%20more%20organized%20and%20maintainable.%0A%0AA%20method%20has%20a%20signature%20and%20a%20body.%20The%20signature%20consists%20of%20the%20name%20of%20the%20method%2C%20the%20return%20type%2C%20and%20the%20parameters.%20The%20body%20consists%20of%20the%20code%20that%20is%20executed%20when%20the%20method%20is%20called.%0A%0AHere%20is%20an%20example%20of%20a%20simple%20method%20in%20Java%3A%0A%0A%60%60%60java%0Apublic%20static%20void%20sayHello()%20%7B%0A%20%20System.out.println(%22Hello%2C%20World!%22)%3B%0A%7D%0A%60%60%60%0A%0AThis%20method%20has%20the%20name%20sayHello%2C%20a%20return%20type%20of%20void%2C%20and%20no%20parameters.%20The%20body%20of%20the%20method%20consists%20of%20a%20single%20line%20of%20code%20that%20prints%20%22Hello%2C%20World!%22%20to%20the%20console.%0A%0A%23%23%23%23%20How%20to%20Call%20a%20Java%20Method%0A%0ATo%20call%20a%20method%20in%20Java%2C%20you%20simply%20use%20the%20name%20of%20the%20method%20followed%20by%20parentheses.%20For%20example%3A%0A%0A%60%60%60java%0AsayHello()%3B%0A%60%60%60%0A%0AThis%20will%20execute%20the%20code%20in%20the%20body%20of%20the%20sayHello%20method%20and%20print%20%22Hello%2C%20World!%22%20to%20the%20console.%0A%0A%23%23%23%23%20Method%20Parameters%20and%20Return%20Values%0A%0AJava%20methods%20can%20have%20parameters%2C%20which%20are%20variables%20that%20are%20passed%20to%20the%20method%20when%20it%20is%20called.%20The%20method%20can%20use%20the%20parameters%20to%20perform%20its%20task%20and%20optionally%20return%20a%20value%20to%20the%20caller.%0A%0AHere%20is%20an%20example%20of%20a%20method%20with%20parameters%20and%20a%20return%20value%3A%0A%0A%60%60%60java%0Apublic%20static%20int%20add(int%20x%2C%20int%20y)%20%7B%0A%20%20return%20x%20%2B%20y%3B%0A%7D%0A%60%60%60%0A%0AThis%20method%20has%20the%20name%20add%2C%20a%20return%20type%20of%20int%2C%20and%20two%20parameters%3A%20x%20and%20y.%20The%20body%20of%20the%20method%20consists%20of%20a%20single%20line%20of%20code%20that%20adds%20the%20values%20of%20x%20and%20y%20and%20returns%20the%20result.%0A%0ATo%20call%20this%20method%2C%20you%20would%20pass%20it%20two%20integers%20as%20arguments%3A%0A%0A%60%60%60java%0Aint%20sum%20%3D%20add(3%2C%204)%3B%0A%60%60%60%0A%0AThis%20would%20assign%20the%20value%207%20to%20the%20variable%20sum.%0A%0AJava%20methods%20are%20a%20powerful%20tool%20that%20allow%20you%20to%20encapsulate%20and%20reuse%20code%20in%20your%20programs.%20They%20make%20it%20easier%20to%20organize%20and%20maintain%20your%20code%2C%20and%20they%20allow%20you%20to%20define%20precise%20interfaces%20for%20interacting%20with%20your%20code.%20By%20using%20methods%20effectively%2C%20you%20can%20write%20more%20efficient%20and%20maintainable%20Java%20programs.

Methods / Functions

Java Basics

%23%23%23%20Java%20Array%0A%0AAn%20array%20is%20a%20collection%20of%20elements%20that%20are%20stored%20in%20a%20contiguous%20block%20of%20memory.%20In%20Java%2C%20an%20array%20is%20an%20object%20that%20holds%20a%20fixed%20number%20of%20values%20of%20the%20same%20data%20type.%0A%0ATo%20create%20an%20array%20in%20Java%2C%20you%20use%20the%20new%20keyword%20followed%20by%20the%20data%20type%20of%20the%20elements%20and%20the%20size%20of%20the%20array.%20Here%20is%20an%20example%20of%20how%20to%20create%20an%20array%20of%20integers%20in%20Java%3A%0A%0A%60%60%60java%0Aint%5B%5D%20numbers%20%3D%20new%20int%5B5%5D%3B%0A%60%60%60%0A%0AThis%20creates%20an%20array%20of%20integers%20with%20a%20size%20of%205.%20You%20can%20also%20initialize%20the%20array%20with%20values%20like%20this%3A%0A%0A%60%60%60java%0Aint%5B%5D%20numbers%20%3D%20%7B1%2C%202%2C%203%2C%204%2C%205%7D%3B%0A%60%60%60%0A%0ATo%20access%20an%20element%20of%20an%20array%2C%20you%20use%20the%20index%20of%20the%20element%20in%20square%20brackets.%20For%20example%3A%0A%0A%60%60%60java%0Aint%20firstElement%20%3D%20numbers%5B0%5D%3B%0Aint%20secondElement%20%3D%20numbers%5B1%5D%3B%0A%60%60%60%0A%0AYou%20can%20also%20use%20a%20loop%20to%20iterate%20over%20all%20the%20elements%20of%20an%20array%3A%0A%0A%60%60%60java%0Afor%20(int%20i%20%3D%200%3B%20i%20%3C%20numbers.length%3B%20i%2B%2B)%20%7B%0A%20%20int%20element%20%3D%20numbers%5Bi%5D%3B%0A%20%20System.out.println(element)%3B%0A%7D%0A%60%60%60%0A%0A%23%23%23%20Java%20List%0A%0AA%20list%20is%20a%20collection%20of%20elements%20that%20can%20grow%20or%20shrink%20dynamically.%20In%20Java%2C%20a%20list%20is%20an%20interface%20that%20represents%20an%20ordered%20collection%20of%20elements.%20There%20are%20several%20implementations%20of%20the%20List%20interface%2C%20including%20ArrayList%20and%20LinkedList.%0A%0ATo%20create%20a%20list%20in%20Java%2C%20you%20use%20the%20new%20keyword%20followed%20by%20the%20class%20that%20implements%20the%20List%20interface.%20Here%20is%20an%20example%20of%20how%20to%20create%20an%20ArrayList%20in%20Java%3A%0A%0A%60%60%60java%0AList%3CString%3E%20names%20%3D%20new%20ArrayList%3C%3E()%3B%0A%60%60%60%0A%0AThis%20creates%20an%20empty%20ArrayList%20of%20strings.%20You%20can%20also%20initialize%20the%20list%20with%20values%20like%20this%3A%0A%0A%60%60%60java%0AList%3CString%3E%20names%20%3D%20new%20ArrayList%3C%3E(Arrays.asList(%22Alice%22%2C%20%22Bob%22%2C%20%22Charlie%22))%3B%0A%60%60%60%0A%0ATo%20add%20an%20element%20to%20a%20list%2C%20you%20use%20the%20add%20method%3A%0A%0A%60%60%60java%0Anames.add(%22Dave%22)%3B%0A%60%60%60%0A%0ATo%20remove%20an%20element%20from%20a%20list%2C%20you%20use%20the%20remove%20method%3A%0A%0A%60%60%60java%0Anames.remove(%22Bob%22)%3B%0A%60%60%60%0A%0ATo%20access%20an%20element%20of%20a%20list%2C%20you%20use%20the%20get%20method%20and%20pass%20it%20the%20index%20of%20the%20element%3A%0A%0A%60%60%60java%0AString%20firstElement%20%3D%20names.get(0)%3B%0AString%20secondElement%20%3D%20names.get(1)%3B%0A%60%60%60%0A%0AYou%20can%20also%20use%20a%20loop%20to%20iterate%20over%20all%20the%20elements%20of%20a%20list%3A%0A%0A%60%60%60java%0Afor%20(String%20name%20%3A%20names)%20%7B%0A%20%20System.out.println(name)%3B%0A%7D%0A%60%60%60%0A%0AIn%20this%20lesson%2C%20we%20learned%20about%20arrays%20and%20lists%20in%20Java.%20Arrays%20are%20fixed-size%20collections%20of%20elements%2C%20while%20lists%20are%20dynamic%20collections%20of%20elements.%20Both%20are%20useful%20for%20storing%20and%20manipulating%20data%20in%20Java%20programs.

Array & List

%23%23%23%20Java%20Map%0A%0AA%20map%20is%20a%20collection%20of%20key-value%20pairs.%20In%20Java%2C%20a%20map%20is%20an%20interface%20that%20represents%20a%20mapping%20of%20keys%20to%20values.%20There%20are%20several%20implementations%20of%20the%20Map%20interface%2C%20including%20HashMap%20and%20TreeMap.%0A%0ATo%20create%20a%20map%20in%20Java%2C%20you%20use%20the%20new%20keyword%20followed%20by%20the%20class%20that%20implements%20the%20Map%20interface.%20Here%20is%20an%20example%20of%20how%20to%20create%20a%20HashMap%20in%20Java%3A%0A%0A%60%60%60java%0AMap%3CString%2C%20Integer%3E%20grades%20%3D%20new%20HashMap%3C%3E()%3B%0A%60%60%60%0A%0AThis%20creates%20an%20empty%20HashMap%20that%20maps%20strings%20(the%20keys)%20to%20integers%20(the%20values).%0A%0ATo%20add%20a%20key-value%20pair%20to%20a%20map%2C%20you%20use%20the%20put%20method%3A%0A%0A%60%60%60java%0Agrades.put(%22Alice%22%2C%2090)%3B%0Agrades.put(%22Bob%22%2C%2080)%3B%0A%60%60%60%0A%0ATo%20get%20the%20value%20for%20a%20particular%20key%2C%20you%20use%20the%20get%20method%3A%0A%0A%60%60%60java%0Aint%20aliceGrade%20%3D%20grades.get(%22Alice%22)%3B%0Aint%20bobGrade%20%3D%20grades.get(%22Bob%22)%3B%0A%60%60%60%0A%0ATo%20remove%20a%20key-value%20pair%20from%20a%20map%2C%20you%20use%20the%20remove%20method%3A%0A%0A%60%60%60java%0Agrades.remove(%22Bob%22)%3B%0A%60%60%60%0A%0AYou%20can%20also%20use%20the%20keySet%20method%20to%20get%20a%20set%20of%20all%20the%20keys%20in%20the%20map%3A%0A%0A%60%60%60java%0ASet%3CString%3E%20keys%20%3D%20grades.keySet()%3B%0A%60%60%60

%23%23%23%20Java%20Set%0A%0AA%20set%20is%20a%20collection%20of%20unique%20elements.%20In%20Java%2C%20a%20set%20is%20an%20interface%20that%20represents%20a%20collection%20of%20elements%20that%20does%20not%20allow%20duplicate%20values.%20There%20are%20several%20implementations%20of%20the%20Set%20interface%2C%20including%20HashSet%20and%20TreeSet.%0A%0ATo%20create%20a%20set%20in%20Java%2C%20you%20use%20the%20new%20keyword%20followed%20by%20the%20class%20that%20implements%20the%20Set%20interface.%20Here%20is%20an%20example%20of%20how%20to%20create%20a%20HashSet%20in%20Java%3A%0A%0A%60%60%60java%0ASet%3CString%3E%20names%20%3D%20new%20HashSet%3C%3E()%3B%0A%60%60%60%0A%0AThis%20creates%20an%20empty%20HashSet%20of%20strings.%0A%0ATo%20add%20an%20element%20to%20a%20set%2C%20you%20use%20the%20add%20method%3A%0A%0A%60%60%60java%0Anames.add(%22Alice%22)%3B%0Anames.add(%22Bob%22)%3B%0A%60%60%60%0A%0ATo%20check%20if%20an%20element%20is%20in%20a%20set%2C%20you%20use%20the%20contains%20method%3A%0A%0A%60%60%60java%0Aif%20(names.contains(%22Alice%22))%20%7B%0A%20%20System.out.println(%22Alice%20is%20in%20the%20set.%22)%3B%0A%7D%0A%60%60%60%0A%0ATo%20remove%20an%20element%20from%20a%20set%2C%20you%20use%20the%20remove%20method%3A%0A%0A%60%60%60java%0Anames.remove(%22Bob%22)%3B%0A%60%60%60%0A%0AYou%20can%20also%20use%20a%20loop%20to%20iterate%20over%20all%20the%20elements%20of%20a%20set%3A%0A%0A%60%60%60java%0Afor%20(String%20name%20%3A%20names)%20%7B%0A%20%20System.out.println(name)%3B%0A%7D%0A%60%60%60

Collection Framework

In%20this%20lesson%2C%20we%20will%20learn%20about%20two%20important%20concepts%20in%20Java%3A%20classes%20and%20inheritance.%0A%0A%23%23%23%20Java%20Class%0A%0AA%20class%20is%20a%20template%20for%20creating%20objects.%20In%20Java%2C%20a%20class%20is%20a%20blueprint%20that%20defines%20the%20properties%20and%20methods%20of%20an%20object.%20A%20class%20has%20three%20parts%3A%0A%0A*%20Fields%3A%20variables%20that%20hold%20the%20state%20of%20an%20object%0A*%20Methods%3A%20functions%20that%20define%20the%20behavior%20of%20an%20object%0A*%20Constructors%3A%20special%20methods%20that%20are%20called%20when%20an%20object%20is%20created%0A%0AHere%20is%20an%20example%20of%20a%20simple%20class%20in%20Java%3A%0A%0A%60%60%60java%0Apublic%20class%20Person%20%7B%0A%20%20%2F%2F%20fields%0A%20%20private%20String%20name%3B%0A%20%20private%20int%20age%3B%0A%0A%20%20%2F%2F%20methods%0A%20%20public%20void%20setName(String%20name)%20%7B%0A%20%20%20%20this.name%20%3D%20name%3B%0A%20%20%7D%0A%0A%20%20public%20String%20getName()%20%7B%0A%20%20%20%20return%20this.name%3B%0A%20%20%7D%0A%0A%20%20public%20void%20setAge(int%20age)%20%7B%0A%20%20%20%20this.age%20%3D%20age%3B%0A%20%20%7D%0A%0A%20%20public%20int%20getAge()%20%7B%0A%20%20%20%20return%20this.age%3B%0A%20%20%7D%0A%7D%0A%60%60%60%0A%0AThis%20class%20has%20two%20fields%3A%20name%20and%20age.%20It%20has%20four%20methods%3A%20setName%2C%20getName%2C%20setAge%2C%20and%20getAge.%20These%20methods%20allow%20you%20to%20set%20and%20get%20the%20values%20of%20the%20name%20and%20age%20fields.%0A%0ATo%20create%20an%20object%20from%20a%20class%2C%20you%20use%20the%20new%20keyword%20followed%20by%20the%20class%20name%20and%20constructor%20arguments%3A%0A%0A%60%60%60java%0APerson%20person%20%3D%20new%20Person()%3B%0A%60%60%60%0A%0AThis%20creates%20an%20instance%20of%20the%20Person%20class%20and%20assigns%20it%20to%20the%20person%20variable.%20You%20can%20then%20use%20the%20methods%20of%20the%20Person%20class%20to%20set%20and%20get%20the%20values%20of%20the%20object's%20fields%3A%0A%0A%60%60%60java%0Aperson.setName(%22Alice%22)%3B%0A%60%60%60%0A%0A%23%23%23%20What%20is%20Inheritance%3F%0A%0AInheritance%20is%20a%20mechanism%20that%20allows%20you%20to%20create%20a%20new%20class%20that%20is%20a%20modified%20version%20of%20an%20existing%20class.%20The%20new%20class%20is%20called%20the%20subclass%2C%20and%20the%20existing%20class%20is%20the%20superclass.%20The%20subclass%20inherits%20the%20properties%20and%20methods%20of%20the%20superclass%20and%20can%20also%20have%20its%20own%20properties%20and%20methods.%0A%0AHere%20is%20an%20example%20of%20inheritance%20in%20Java%3A%0A%0A%60%60%60java%0Apublic%20class%20Animal%20%7B%0A%20%20%2F%2F%20fields%0A%20%20protected%20String%20name%3B%0A%0A%20%20%2F%2F%20methods%0A%20%20public%20void%20setName(String%20name)%20%7B%0A%20%20%20%20this.name%20%3D%20name%3B%0A%20%20%7D%0A%0A%20%20public%20String%20getName()%20%7B%0A%20%20%20%20return%20this.name%3B%0A%20%20%7D%0A%7D%0A%0Apublic%20class%20Dog%20extends%20Animal%20%7B%0A%20%20%2F%2F%20fields%0A%20%20private%20String%20breed%3B%0A%0A%20%20%2F%2F%20methods%0A%20%20public%20void%20setBreed(String%20breed)%20%7B%0A%20%20%20%20this.breed%20%3D%20breed%3B%0A%20%20%7D%0A%0A%20%20public%20String%20getBreed()%20%7B%0A%20%20%20%20return%20this.breed%3B%0A%20%20%7D%0A%7D%0A%60%60%60%0A%0AIn%20this%20example%2C%20the%20Animal%20class%20is%20the%20superclass%20and%20the%20Dog%20class%20is%20the%20subclass.%20The%20Dog%20class%20inherits%20the%20name%20field%20and%20the%20setName%20and%20getName%20methods%20from%20the%20Animal%20class.%20It%20also%20has%20its%20own%20breed%20field%20and%20setBreed%20and%20getBreed%20methods.%0A%0ATo%20create%20an%20object%20of%20the%20Dog%20class%2C%20you%20use%20the%20new%20keyword%20and%20the%20constructor%20arguments%3A%0A%0A%60%60%60java%0ADog%20dog%20%3D%20new%20Dog()%3B%0A%60%60%60%0A%0AYou%20can%20then%20use%20the%20inherited%20and%20custom%20methods%20of%20the%20Dog%20class%20to%20set%20and%20get%20the%20values%20of%20the%20object's%20fields%3A%0A%0A%60%60%60java%0Adog.setName(%22Buddy%22)%3B%0Adog.setBreed(%22Labrador%22)%3B%0A%60%60%60%0A%0A%23%23%23%23%20Why%20Use%20Inheritance%3F%0A%0AThere%20are%20several%20reasons%20to%20use%20inheritance%20in%20Java%3A%0A%0A*%20Code%20reuse%3A%20You%20can%20reuse%20the%20code%20from%20the%20superclass%20in%20the%20subclass%2C%20which%20saves%20time%20and%20reduces%20the%20risk%20of%20errors.%0A*%20Polymorphism%3A%20You%20can%20use%20a%20subclass%20object%20in%20the%20same%20way%20as%20a%20superclass%20object%2C%20which%20allows%20you%20to%20write%20more%20flexible%20and%20reusable%20code.%0A*%20Simplicity%3A%20You%20can%20create%20a%20subclass%20that%20only%20includes%20the%20modifications%20you%20need%2C%20which%20makes%20your%20code%20simpler%20and%20easier%20to%20understand.%0A%0AInheritance%20is%20a%20way%20to%20create%20a%20new%20class%20that%20is%20a%20modified%20version%20of%20an%20existing%20class.%20It%20allows%20you%20to%20reuse%20code%2C%20write%20more%20flexible%20and%20reusable%20code%2C%20and%20create%20simpler%20and%20easier%20to%20understand%20classes.

Class & Inheritance

Abstraction

Polymorphism

Encapsulation

Java OOP

%23%23%23%20What%20is%20Interface%3F%0A%0AAn%20interface%20is%20a%20collection%20of%20abstract%20methods%2C%20which%20are%20methods%20that%20do%20not%20have%20an%20implementation.%20An%20interface%20specifies%20what%20an%20implementing%20class%20should%20do%2C%20but%20not%20how%20it%20should%20do%20it.%20Here%20is%20an%20example%20of%20an%20interface%20in%20Java%3A%0A%0A%60%60%60java%0Apublic%20interface%20Shape%20%7B%0A%20%20double%20getArea()%3B%0A%20%20double%20getPerimeter()%3B%0A%7D%0A%60%60%60%0A%0AThis%20interface%20has%20two%20abstract%20methods%3A%20getArea%20and%20getPerimeter.%20An%20implementing%20class%20must%20provide%20an%20implementation%20for%20these%20methods.%0A%0ATo%20implement%20an%20interface%2C%20a%20class%20must%20use%20the%20implements%20keyword%20and%20the%20name%20of%20the%20interface%3A%0A%0A%60%60%60java%0Apublic%20class%20Circle%20implements%20Shape%20%7B%0A%20%20%2F%2F%20fields%0A%20%20private%20double%20radius%3B%0A%0A%20%20%2F%2F%20methods%0A%20%20%40Override%0A%20%20public%20double%20getArea()%20%7B%0A%20%20%20%20return%20Math.PI%20*%20radius%20*%20radius%3B%0A%20%20%7D%0A%0A%20%20%40Override%0A%20%20public%20double%20getPerimeter()%20%7B%0A%20%20%20%20return%202%20*%20Math.PI%20*%20radius%3B%0A%20%20%7D%0A%0A%20%20%2F%2F%20constructor%0A%20%20public%20Circle(double%20radius)%20%7B%0A%20%20%20%20this.radius%20%3D%20radius%3B%0A%20%20%7D%0A%7D%0A%60%60%60%0A%0AIn%20this%20example%2C%20the%20Circle%20class%20implements%20the%20Shape%20interface%20and%20provides%20an%20implementation%20for%20the%20getArea%20and%20getPerimeter%20methods.%20The%20%40Override%20annotation%20is%20used%20to%20specify%20that%20the%20method%20is%20an%20implementation%20of%20an%20abstract%20method%20from%20the%20interface.%0A%0ATo%20use%20an%20interface%2C%20you%20can%20create%20a%20reference%20variable%20of%20the%20interface%20type%20and%20assign%20it%20an%20object%20of%20a%20class%20that%20implements%20the%20interface%3A%0A%0A%60%60%60java%0AShape%20circle%20%3D%20new%20Circle(5)%3B%0A%60%60%60%0A%0AThis%20creates%20an%20instance%20of%20the%20Circle%20class%20and%20assigns%20it%20to%20the%20circle%20variable%2C%20which%20is%20a%20reference%20to%20the%20Shape%20interface.%20You%20can%20then%20use%20the%20circle%20reference%20to%20call%20the%20%60getArea%60%20and%20%60getPerimeter%60.

Interface

Singleton Pattern

Dependency Injection

Java OOP Extended

Java File & IO

Java Network IO

Java IO

In%20this%20lesson%2C%20we%20will%20learn%20about%20thread%2C%20which%20is%20a%20separate%20flow%20of%20execution%20in%20a%20Java%20program.%0A%0A%23%23%23%20What%20is%20Thread%3F%0A%0AA%20thread%20is%20a%20separate%20flow%20of%20execution%20in%20a%20Java%20program.%20Threads%20allow%20you%20to%20run%20multiple%20tasks%20concurrently%2C%20which%20can%20improve%20the%20performance%20and%20responsiveness%20of%20your%20application.%0A%0AHere%20is%20an%20example%20of%20creating%20a%20thread%20in%20Java%3A%0A%0A%60%60%60java%0Apublic%20class%20HelloThread%20extends%20Thread%20%7B%0A%20%20%40Override%0A%20%20public%20void%20run()%20%7B%0A%20%20%20%20System.out.println(%22Hello%20from%20a%20thread!%22)%3B%0A%20%20%7D%0A%7D%0A%0Apublic%20class%20Main%20%7B%0A%20%20public%20static%20void%20main(String%5B%5D%20args)%20%7B%0A%20%20%20%20HelloThread%20thread%20%3D%20new%20HelloThread()%3B%0A%20%20%20%20thread.start()%3B%0A%20%20%7D%0A%7D%0A%60%60%60%0A%0AIn%20this%20example%2C%20the%20HelloThread%20class%20extends%20the%20Thread%20class%20and%20overrides%20the%20run%20method.%20The%20run%20method%20is%20the%20entry%20point%20for%20the%20thread%20and%20contains%20the%20code%20that%20will%20be%20executed%20by%20the%20thread.%0A%0ATo%20create%20a%20thread%2C%20you%20can%20create%20an%20instance%20of%20a%20class%20that%20extends%20the%20Thread%20class%20and%20call%20the%20start%20method.%20This%20will%20create%20a%20new%20thread%20and%20start%20its%20execution.%0A%0AYou%20can%20also%20create%20a%20thread%20by%20implementing%20the%20Runnable%20interface%20and%20passing%20an%20instance%20of%20the%20interface%20to%20a%20Thread%20constructor%3A%0A%0A%60%60%60java%0Apublic%20class%20HelloRunnable%20implements%20Runnable%20%7B%0A%20%20%40Override%0A%20%20public%20void%20run()%20%7B%0A%20%20%20%20System.out.println(%22Hello%20from%20a%20runnable!%22)%3B%0A%20%20%7D%0A%7D%0A%0Apublic%20class%20Main%20%7B%0A%20%20public%20static%20void%20main(String%5B%5D%20args)%20%7B%0A%20%20%20%20Thread%20thread%20%3D%20new%20Thread(new%20HelloRunnable())%3B%0A%20%20%20%20thread.start()%3B%0A%20%20%7D%0A%7D%0A%60%60%60%0A%0AIn%20this%20example%2C%20the%20HelloRunnable%20class%20implements%20the%20Runnable%20interface%20and%20overrides%20the%20run%20method.%20To%20create%20a%20thread%2C%20you%20can%20create%20an%20instance%20of%20the%20Thread%20class%20and%20pass%20an%20instance%20of%20the%20HelloRunnable%20class%20to%20the%20Thread%20constructor.%0A%0A%23%23%23%23%20Why%20Use%20Thread%3F%0A%0AThere%20are%20several%20reasons%20to%20use%20thread%20in%20Java%3A%0A%0A*%20Concurrency%3A%20You%20can%20use%20thread%20to%20run%20multiple%20tasks%20concurrently%2C%20which%20can%20improve%20the%20performance%20and%20responsiveness%20of%20your%20application.%0A*%20Resource%20sharing%3A%20You%20can%20use%20thread%20to%20share%20resources%20between%20tasks%2C%20which%20can%20reduce%20the%20memory%20usage%20of%20your%20application.%0A*%20Asynchrony%3A%20You%20can%20use%20thread%20to%20perform%20tasks%20asynchronously%2C%20which%20can%20improve%20the%20user%20experience%20of%20your%20application.%0A%0AA%20thread%20is%20a%20separate%20flow%20of%20execution%20in%20a%20Java%20program.%20You%20can%20create%20a%20thread%20by%20extending%20the%20Thread%20class%20or%20implementing%20the%20Runnable%20interface%20and%20passing%20an%20instance%20of%20the%20interface%20to%20a%20Thread%20constructor.%20Threads%20allow%20you%20to%20run%20multiple%20tasks%20concurrently%2C%20share%20resources%2C%20and%20perform%20tasks%20asynchronously.

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