1410: FLEXIBILITY WITH WILDCARD PARAMETERIZED TYPES in Java

Generator QR Code JIS X 0510 in Java 1410: FLEXIBILITY WITH WILDCARD PARAMETERIZED TYPES
1410: FLEXIBILITY WITH WILDCARD PARAMETERIZED TYPES
Encode QR Code ISO/IEC18004 In Java
Using Barcode printer for Java Control to generate, create QR Code image in Java applications.
Capture Conversion
Creating Bar Code In Java
Using Barcode generation for Java Control to generate, create bar code image in Java applications.
Consider the following non-generic method which does not compile:
Bar Code Scanner In Java
Using Barcode decoder for Java Control to read, scan read, scan image in Java applications.
static void fillWithFirstV1(List< > list) { Object firstElement = listget(0); // (1) for (int i = 1; i < listsize(); i++) listset(i, firstElement); // (2) Compile-time error }
Encode Denso QR Bar Code In C#
Using Barcode generation for .NET Control to generate, create QR Code ISO/IEC18004 image in VS .NET applications.
The method should fill any list passed as argument with the element in its first position The call to the set() method is not permitted, as a set operation is not possible with a < > reference (see Table 143, p 684) Using the wildcard to parameterize the list does not work We can replace the wild card with a type parameter of a generic method, as follows:
Making QR Code In VS .NET
Using Barcode generation for ASP.NET Control to generate, create QR Code image in ASP.NET applications.
static <E> void fillWithFirstOne(List<E> list) { E firstElement = listget(0); // (3) for (int i = 1; i < listsize(); i++) listset(i, firstElement); // (4) }
Generate QR In Visual Studio .NET
Using Barcode creator for .NET Control to generate, create QR image in VS .NET applications.
Since the type of the argument is List<E>, we can set and get objects of type E from the list We have also changed the type of the reference firstElement from Object to E in order to set the first element in the list It turns out that if the first method fillWithFirstV1() is re-implemented with a call to the generic method fillWithFirstOne() It all works well:
Encoding QR Code ISO/IEC18004 In VB.NET
Using Barcode drawer for VS .NET Control to generate, create Quick Response Code image in Visual Studio .NET applications.
static void fillWithFirstV2(List< > list) { fillWithFirstOne(list); // (5) Type conversion }
Create USS Code 128 In Java
Using Barcode printer for Java Control to generate, create Code 128C image in Java applications.
The wildcard in the argument of the fillWithFirstV1() has a type capture In the call to the fillWithFirstOne() method at (5), this type capture is converted to the type E This conversion is called capture conversion, and it comes into play under certain conditions, which are beyond the scope of this book
Making UPC-A Supplement 2 In Java
Using Barcode generation for Java Control to generate, create UPC-A Supplement 2 image in Java applications.
1410 Flexibility with Wildcard Parameterized Types Nested Wildcards
Bar Code Printer In Java
Using Barcode maker for Java Control to generate, create bar code image in Java applications.
We have seen that the subtype relationship is invariant for the unbounded type parameter <T>:
Make Barcode In Java
Using Barcode drawer for Java Control to generate, create bar code image in Java applications.
Collection<Number> colNum; Set<Number> setNum; Set<Integer> setInt; colNum = setNum; // (1) Set<Number> <: Collection<Number> colNum = setInt; // (2) Compile-time error!
Paint USS Code 39 In Java
Using Barcode encoder for Java Control to generate, create Code 39 image in Java applications.
CHAPTER 14: GENERICS
Generating ANSI/AIM Codabar In Java
Using Barcode generation for Java Control to generate, create Codabar image in Java applications.
The same is true when concrete parameterized types are used as actual type parameters, implementing what are called nested parameterized types, ie, using parameterized types as type parameters
Generating Barcode In VS .NET
Using Barcode encoder for ASP.NET Control to generate, create barcode image in ASP.NET applications.
Collection<Collection<Number>> colColNum; // Collection of Collections of Number Set<Collection<Number>> setColNum; // Set of Collections of Number Set<Set<Integer>> setSetInt; // Set of Sets of Integer colColNum = setColNum; // (3) Set<Collection<Number>> <: // Collection<Collection<Number>> colColNum = setSetInt; // (4) Compile-time error! setColNum = setSetInt; // (5) Compile-time error!
Encode Code128 In VB.NET
Using Barcode creator for .NET framework Control to generate, create Code 128 Code Set B image in .NET applications.
Again, we can use the upper bounded wildcard to induce subtype covariance The upper bounded wildcard is applied at the top level in the code below The assignment below at (8) is not compatible, because Set<Set<Integer>> is not a subtype of Collection< extends Collection<Number>>
ANSI/AIM Code 128 Creator In .NET
Using Barcode maker for ASP.NET Control to generate, create Code128 image in ASP.NET applications.
Collection< extends Collection<Number>> colExtColNum; colExtColNum = colColNum; // (6) Collection<Collection<Number>> <: // Collection< extends Collection<Number>> colExtColNum = setColNum; // (7) Set<Collection<Number>> <: // Collection< extends Collection<Number>> colExtColNum = setSetInt; // (8) Compile-time error!
GS1 - 12 Drawer In VS .NET
Using Barcode maker for ASP.NET Control to generate, create UPC-A Supplement 2 image in ASP.NET applications.
In the code below, the wildcard is applied at the inner-most level:
Bar Code Creator In VB.NET
Using Barcode creator for Visual Studio .NET Control to generate, create barcode image in Visual Studio .NET applications.
Collection<Collection< extends colColExtNum = colColNum; colColExtNum = setColNum; colColExtNum = setSetInt; Number>> colColExtNum; // (9) Compile-time error! // (10) Compile-time error! // (11) Compile-time error!
Barcode Creation In VS .NET
Using Barcode maker for Visual Studio .NET Control to generate, create bar code image in Visual Studio .NET applications.
The assignments above show that the upper bounded wildcard induces subtype covariance only at the top level In (9), type A (=Collection<Number>) is a subtype of type B (=Collection< extends Number>), but because subtype covariance relationship does not hold between parameterized types, the type Collection<A> (=Collection<Collection<Number>>) is not a subtype of Collection<B> (= Collection<Collection< extends Number>>) The above discussion also applies when a parameterized type has more than one type parameter:
Creating UCC - 12 In .NET
Using Barcode generation for Visual Studio .NET Control to generate, create EAN / UCC - 14 image in VS .NET applications.
Map<Number, String> mapNumStr; Map<Integer, String> mapIntStr; mapNumStr = mapIntStr;
// (12) Compile-time error!
Again, the upper bounded wildcard can only be used at the top level to induce subtype covariance:
Map<Integer, extends Collection<String>> mapIntExtColStr; Map<Integer, Collection< extends String>> mapIntColExtStr; Map<Integer, Collection<String>> mapIntColStr; Map<Integer, Set<String>> mapIntSetStr; mapIntExtColStr = mapIntColStr;// (13) Map<Integer, Collection<String>> <: // Map<Integer, extends Collection<String>> mapIntExtColStr = mapIntSetStr;// (14) Map<Integer, Set<String>> <: // Map<Integer, extends Collection<String>>
1410: FLEXIBILITY WITH WILDCARD PARAMETERIZED TYPES mapIntColStr = mapIntSetStr; mapIntColExtStr = mapIntColStr; mapIntColExtStr = mapIntSetStr; // (15) Compile-time error! // (16) Compile-time error! // (17) Compile-time error!