Learn from teacher Wang Generics (vii): Restrict wildcard characters

restricting wildcard characters
Keynote Teacher: Wang Shaohua QQ Group: 483773664 Learning Goals

1. Limit the upper boundary of a wildcard

2. Limit the bottom bounds of the wildcard

3. Qualifying wildcard is some type of interface

First, set the upper limit of the type wildcard character
(a) demand

If we don't want this list<?> to be any generic list, just want to indicate that it is the parent class of a generic list of a certain type.

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For example, an element in a list can only be an employee class and its subclasses.

(ii) grammar

1	<? extendssuperClass>

(iii) achieving

12	publicclassPerson {}

12	publicclass Employee extendsPerson{}

12	publicclass Manager extendsEmployee{}

12345

public  class   needs1 {      public   void   test (list<?  extends   employee> list {                 } }

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Second, type wildcard character lower bound (a) syntax

1	<? supersubClass>

Scope of the parameter type: itself and its parent class

(b) Test code

12345

public  class   needs1 {      public   void   test (list<?  Super   employee> list) {                 } }

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Three, interface (i) syntax

1	<? extendsComparable>

Only allow generics to invoke references to implementation classes that implement the comparable interface

Iv. Learning Video URL:

Http://edu.51cto.com/course/course_id-6083.html

From for notes (Wiz)

Learn from teacher Wang Generics (vii): Restrict wildcard characters