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5. Java collections and Generics. 3. Generics презентация
Содержание
- 1. 5. Java collections and Generics. 3. Generics
- 2. Generics Basics JDK 5.0 introduces generics Generics
- 3. Generic Classes public class ClassName{
- 4. Generic Objects You need to set a
- 5. How Generics Work In the invocation all
- 6. Exercise. Print List Create a class with
- 7. Exercise. Print List See 531FirstGeneric project for the full text
- 8. Generics Inheritance In general, if Sub is
- 9. Generic Interfaces Generic interfaces are similar to
- 10. Generic Methods Type parameters can also be
- 11. Generic Method Example class ArrayAlg {
- 12. Generic Method Call When you call a
- 13. Wildcards What is the supertype of all
- 14. Bounded Wildcards ? extends class_name ?
- 15. Bounded Wildcards Example public static double sumOfList(List
- 16. Home Exercise 5.3.2 ( 1 of 2)
- 17. Home Exercise 5.3.2 (2 of 2)
- 18. Manuals http://docs.oracle.com/javase/tutorial/extra/generics/index.html * Infopulse Training Center
Generics Basics JDK 5.0 introduces generics Generics allow you to abstract over types The most common examples are container types, such as those in the Collections hierarchy * Infopulse Training Center
Слайд 2Generics Basics
JDK 5.0 introduces generics
Generics allow you to abstract over types
The
most common examples are container types, such as those in the Collections hierarchy
*
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Слайд 3Generic Classes
public class ClassName{
class body
}
Parametric type T can be
used in the class body as usual type:
private T a;
public void set(T a) { this.a = a; }
public T get() { return a; }
private T a;
public void set(T a) { this.a = a; }
public T get() { return a; }
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Слайд 4Generic Objects
You need to set a type in when creating
an object of generic class:
public class GenClass<Т>{
. . . . .
}
GenClass cInt = new GenClass();
public class GenClass<Т>{
. . . . .
}
GenClass
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Слайд 5How Generics Work
In the invocation all occurrences of the formal type
parameter are replaced by the actual type argument
The compiler can check the type correctness of the program at compile-time
Primitive types cannot use as actual types
The compiler can check the type correctness of the program at compile-time
Primitive types cannot use as actual types
*
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Слайд 6Exercise. Print List
Create a class with list of objects of an
arbitrary given class with two methods:
add for accumulation data in the list
printList with a boolean parameter to print odd or even elements of the list accordingly to parameter’s value
add for accumulation data in the list
printList with a boolean parameter to print odd or even elements of the list accordingly to parameter’s value
Слайд 8Generics Inheritance
In general, if Sub is a subtype (subclass or subinterface)
of Base, and G is some generic type declaration, it is not the case that G is a subtype of G
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Слайд 9Generic Interfaces
Generic interfaces are similar to generic classes:
public interface List{
void add(E x);
Iterator
}
public interface Iterator
E next();
boolean hasNext();
}
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Слайд 10Generic Methods
Type parameters can also be declared within method and constructor
signatures to create generic methods and generic constructors:
public void inspect(U u){ . . . }
Type inference feature allows you to invoke a generic method as you would an ordinary method, without specifying a type between angle brackets
public void inspect(U u){ . . . }
Type inference feature allows you to invoke a generic method as you would an ordinary method, without specifying a type between angle brackets
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Слайд 11Generic Method Example
class ArrayAlg
{
public static T getMiddle(T[] a)
{
return a[a.length / 2];
}
}
You can define generic methods both inside ordinary classes and inside generic classes
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Слайд 12Generic Method Call
When you call a generic method, you can place
the actual types, enclosed in angle brackets, before the method name:
String[] names = { "John", "Q.", "Public" };
String middle = ArrayAlg.getMiddle(names);
String[] names = { "John", "Q.", "Public" };
String middle = ArrayAlg.
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Слайд 13Wildcards
What is the supertype of all kinds of collections?
Collection is not
such supertype due to generics inheritance rule
Collection (pronounced "collection of unknown"), that is, a collection whose element type matches anything
Collection (pronounced "collection of unknown"), that is, a collection whose element type matches anything
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Слайд 14Bounded Wildcards
? extends class_name
? stands for an unknown type
that this
unknown type is a subtype of class_name
example: List
Code would be read as "an unknown type that is a supertype of class_name, possibly class_name itself
example: List
Code would be read as "an unknown type that is a supertype of class_name, possibly class_name itself
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Слайд 15Bounded Wildcards Example
public static double sumOfList(List
s = 0.0;
for (Number n : list) s += n.doubleValue(); return s;
}
for (Number n : list) s += n.doubleValue(); return s;
}
*
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Слайд 16Home Exercise 5.3.2 ( 1 of 2)
Create TBill class that
saves deal for buying treasury bills (nominal, price, amount of bills, maturity date) and calculating deal income as follows:
income = (nominal – price) * amount
income = (nominal – price) * amount
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Слайд 17Home Exercise 5.3.2 (2 of 2)
Create DealAnalisys class that saves
deals of any type (depo – single, barrier, month capitalization, TBill)
Create compareIncome method that compares yield of the deal that saved in the class object and deal given as method’s parameter
Create compareIncome method that compares yield of the deal that saved in the class object and deal given as method’s parameter
*
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Слайд 18Manuals
http://docs.oracle.com/javase/tutorial/extra/generics/index.html
*
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