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Match Expressions

Similar to switch in java but * No need of break as one match will terminate successive cases execution. Also break is repeatation for each case statement. If we forget break then multiple cases will execute. * Case works only with numbers and strings in java but scala will support all types * match works as function so it can return values * has result = variable match { case xxx: "String to be returned" case yyy: "String to be returned" }

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• If and else can return value

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var message:String = if (condition) 
	"Hi Dear"
else
	"Hello Dear"

println(message) // prints either one

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• Return keyword is not mandatory
• Default values can be defined for method params

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def greet(name:String="Guest") {
	println("Hello ," + name);
}
greet() will print "Hello Guest"

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• Dynamic language will not be strict type which let types to be inferred at the runtime
• Interpreter is choosen for lanugage which will not be converted and then executed instead they will be read and interpreted simultaneously
• Interpreter actually "Compiles + Executes" at the same time.
• Concurrent app should have minimal shared objects. and shared objects should be immutable.
• When declaring arguments, var/val is mandatory.
  • def greet(0

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•                     		Any
    			AnyVal	-----				----	AnyRef
  

int - long - double - char - boolean --- All custom classes and java classes

• Scala has only class or abstract class and no interface concept
• Traits are replacements for interface
  • traits are not interface or class
  • interface are only for communication and not part of OOPS
  • No implements keyword because no interface in scala
• var properties of super class cannot be overriden, only val properties can be. ###########
• constructors are functions and values can be passed by name like functions
• Access Specifiers
  • private : class will not able accessible anywhere
  • protected : accisible only if inherited either inside package or outside
  • no-modifier : by default public : for both class and functions
• Every function is an object in scala #####
• Scala has a class Function.java which will be class for all fucntions in scala
• Scala can be Object oriented, Functional or Scripting language
• Main method also can have inner functions similar to other functions
• Anonymous Functions
  • Function defintion will have four part, definition, name, arguments and body def greet() { println("Good Morning.") }
  • Remove name and definitions () => { println("Good Morning.") }
  • Closure in nothing but lambda in java which is anonymous functions
  • => is called <<<<<<>>>>>>> in javascript
  • -> java uses <<<<<<<<>>>>>>>>
  • scala > :type a () => Unit
• By default var will have "Nothing" in scala, so it handles NPEs
• Default return type is "Unit" in scala. if there any return types then it iwll override "Unit" type
• When we print a method returning nothing which is actually "Unit" then it prints "()"
  • println(main()) // Main returning nothing
• Function is not under "Any" hierarchy. Function is not Any type

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Misc

• No need of installing anyting for scala. just download plugins wihch does come with scala libraries. JDK is enough for running scala.
• java supports only multi-level and hierarchy inheritance. and does not support multiple and hybrid inheritance
• Interface Issues
  • Interface forces for impl of methods. which is dulicate of code
  • Two interface methods have same method and class is overriding then which method will get overriden? or error? Ans: No error
• Mixin : is alternative to support multiple inheritence. Scala supports multiple inheritence through Mixin
  • Mixing is not inheritance , it is actually code copied or mixed to class. so we cannot call super in case of Mixin and instead all be a part of your class
• Byte-code instrumentation
• java 8 default methods in interface are called DEFEENDER methods
• Closure in nothing but lambda in java which is anonymous functions

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Scala Topics

closures Anonymous functions Higher order functions yield keyword #####