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enum
small, finite/fixed set known at compile time no need to extend

switch
works on primitive type, enum, string

primitives
boxed primitives(reference)

equality
override equal()
override hashcode()

illegalException
Extend
Throw
Catch

exceptional conditions
throw exceptions
cat exceptions

static
happens at compile time
belongs to a class
fields:one variable for the whole class rather than one per object
methods:associated with the class that doesnt depend on an instance
classes:helper class with strong association

Encapsulation private, protected, public

Polymorphism Assigning behavior or value in a subclass to something that was already declared in the main class
@overload
same name & differnt argument type | different return types
@override
same name & same argument & same return type

Interface
has only method declarations

Abstract class
abstract method : only abstract methods
implemented or overrided in subclass
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