Scala in Depth 6 Scala type system

Answer the previous article.

1. Is there also a syntax for declaring upper bound and Lower Boud in Java? Some, such as:

List<e extends numeric> list<e Upper integer>

What is the difference between list<?> and list<object> in 2.Java?

List<?> represents any type of list that can be assigned to it

List<object> represents the type of element in list is arbitrary

Package Tstge;import java.util.*;p ublic class Tst {public static void main (string[] args) {arraylist<?>        Mylist1 = null;        Arraylist<object> mylist2 = null;        arraylist<integer> mylist3 = new arraylist<integer> (); Mylist2 = Mylist3; error!    Type Mismatch:cannot convert from arraylist<integer> to arraylist<object> mylist1 = Mylist3; }}

The type of 3.Java can usually be translated directly into the Scala type. But like Iterator<?> iterator< Extends component> such a type how to translate it?

Iterator[t] Forsome {type T} or Iterator[_]
Iterator[t] Forsome {type T <: Component}

About Forsome,stack overflow has a very good introduction:

Http://stackoverflow.com/questions/15186520/scala-any-vs-underscore-in-generics

4.View bound

def foo[a <% B] (x:a) = X

This means that where you call the Foo method, you must be able to see the conversion function from type A to type B, which is equivalent to

def Foo[a] (x:a) (implicit $ev 0:a = B) = X

5. Context bound

def Foo[a:b] (x:a) = X

TheFooMethod defines a constraintA:b. This constraint means the parameter
Xis of typeAa nd there must is an implicit value b[a]  available when calling method
foo. Context bounds can be rewritten as follows

def Foo[a] (x:a) (implicit $ev 0:b[a]) = X

The current context must have an implicit Val of type b[a]

Scala in Depth 6 Scala type system