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I like your notes. And I will keep working on making this repo closer to what is taught in Coursera #1

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I like your notes. And I will keep working on making this repo closer to what is taught in Coursera #1

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Update Lecture 3.2 - How Classes Are Organized.md
zjplab Sep 16, 2019
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Update Lecture 3.2 - How Classes Are Organized.md
zjplab Sep 16, 2019
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Update Lecture 3.2 - How Classes Are Organized.md
zjplab Sep 16, 2019
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23 changes: 17 additions & 6 deletions Week 3 - Data and Abstraction/Lecture 3.2 - How Classes Are Organized.md
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+ In order to import a named type from a package we do:

import progfun.examples.Hello
import progfun.examples.{Hello, Rational} // imports more than one
import progfun.examples.Hello //named import
import progfun.examples.{Hello, Rational} // imports more than one, named import
import progfun.examples._ // imports everything under examples

+ All members of the packages `scala`, `java.lang` and the singleton object `scala.Predef` are auto imported.
+ All members of the packages:
- `scala`
- `java.lang`
- and the singleton object `scala.Predef` are auto imported.

### Traits
+ In Scala, a class can have only one superclass. It's a single inheritance language.
+ If a class wants to inherit code from more than one supertype we use `traits`.
+ `traits` are declared like an `abstract class` with the keyword `trait` instead of `abstract class`
```scala
trait Planar {
def height: Int
def width: Int
def surface = height * width
}
```
+ Classes, objects and traits can inherit from at most one class but from many traits.
```scala
class Square extends Shape with Planar with Movable
```
+ Classes inherit code from a trait with the `with` keyword.

class Square extends Shape with Planar with Movable

+ traits cannot have `val` parameters. But unlike interfaces in Java it can contain concrete methods and fields.

### Scala class hierarchy
+ [Class hierarchy](http://www.scala-lang.org/old/sites/default/files/images/classhierarchy.png)
![Class hierarchy](https://lh3.googleusercontent.com/Hz5G9eaSlV4yrkxsDZWNNsRpDmarjSQjBUTw7ODeqegy4u03pVYJ36EXOleYEt6t5plCsxxwZ8dCDdNtNBOJJemXnOnRlNDQm-ytc3kxIuEtYU04RE74OhlCMFwDkCM9DEL2efmTbUVg9bW0Ban8dLfOy0Nl2fxeFDtEfE8tezFffz-SnW8NL0ghyq-CqJC-1YIxizaiLoocQdlzfGAgDkTtaOG2Obd_F3wIp5XSjhaN8X6U7Qf7MfYqRF7WRX2MFksFl2Go3Ne-JWzUDUD0h3yy8grua66P6NHERjm2iBk3m7pCwxtehdwELJ8iliHr7C8P8rZ4Uz8AuRwC57GmiOY36MfckDSgvjJVY38J8oVl4WUiRaQEI-HvT9p0Soqq33xc4zAZ5M8F1G8nnVufJwbaY9l7fSOM5f3P5XVb6UbzhaZqno5yZjYm44j6scIzII3txaIYB7fVX4Uu7wakPXEOj_M4IWHK6hvuiZ95aVHqCY339JbIHx8sfyvQ63-9FfVgA35MI1gbpdhSbPHcw7RCeU6tnB1TH3Dnog7MGXH8p_Om95lItqDV-Ah5uZAnW8gNmO29FH4ljDwJOSEKL4o3GBBS_zO4fTWMKCOh_DfDfAy3FahovYKTRYpEpYpDyEt8Nt8iLXZFpvAB3EWerFv6ICMiuRlnbO7N3TpwBhNjCcNyBm9JGw=w1347-h782-no)
+ `Scala.Any` is at the top of scala class hierarchy and is the base type of all scala types. It is also the base type that defines universal methods like `toString`, `equals`, `hashCode`, `==`, `!=`, etc
+ `Scala.AnyVal` is a subclass of `Scala.Any` and is the base class of all primitive types like `Byte`, `Int`, `Double`, etc
+ `Scala.AnyRef` is a base type of all reference types. Alias of `java.lang.Object`. `scala.Iterable`, `scala.Seq`, `scala.List` are base classes of `scala.AnyRef` but they also implement the trait `Scala.ScalaObject`
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