visual basic 2010 barcode generator Converting C++ Multiple-Inheritance Hierarchies in Java

Making QR Code JIS X 0510 in Java Converting C++ Multiple-Inheritance Hierarchies

Converting C++ Multiple-Inheritance Hierarchies
Painting QR In Java
Using Barcode generation for Java Control to generate, create QR Code image in Java applications.
QR Code Decoder In Java
Using Barcode reader for Java Control to read, scan read, scan image in Java applications.
C++ allows one class to inherit two or more base classes at the same time Java does not To understand the difference, consider the two hierarchies depicted here:
Bar Code Generator In Java
Using Barcode creation for Java Control to generate, create bar code image in Java applications.
Scanning Barcode In Java
Using Barcode reader for Java Control to read, scan read, scan image in Java applications.
In both cases, subclass C inherits classes A and B However, in the hierarchy on the left, C inherits both A and B at the same time In the one on the right, B inherits A, and C
Paint Quick Response Code In Visual C#
Using Barcode printer for Visual Studio .NET Control to generate, create QR Code ISO/IEC18004 image in .NET applications.
QR Code ISO/IEC18004 Printer In Visual Studio .NET
Using Barcode generation for ASP.NET Control to generate, create QR-Code image in ASP.NET applications.
- 654 -
Making QR Code JIS X 0510 In Visual Studio .NET
Using Barcode drawer for .NET Control to generate, create QR Code image in .NET framework applications.
QR Code Printer In Visual Basic .NET
Using Barcode drawer for .NET Control to generate, create QR Code 2d barcode image in .NET framework applications.
inherits B By not allowing the inheritance of multiple base classes by a single subclass, Java greatly simplifies the inheritance model Multiple inheritance carries with it several special cases that must be handled This adds overhead to both the compiler and the run-time system, while providing only marginal benefit for the programmer Since C++ supports multiple inheritance and Java does not, you may have to deal with this issue when porting C++ applications to Java While every situation is different, two general pieces of advice can be offered First, in many cases, multiple inheritance is employed in a C++ program when there is actually no need to do so When this is the case, just convert the class structure to a single-inheritance hierarchy For example, consider this C++ class hierarchy that defines a class called House: class Foundation { // }; class Walls { // }; class Rooms { // }; class House : public Foundation, Walls, Rooms { // }; Notice that House multiply inherits Foundation, Walls, and Rooms While there is nothing wrong with structuring a C++ hierarchy like this, it is not necessary For example, here is the same set of classes structured for Java: class Foundation { // } class Walls extends Foundation { // } class Rooms extends Walls { // } class House extends Rooms { // } Here, each class extends the preceding one, with House becoming the final extension Sometimes a multiple inheritance hierarchy is more readily converted by including objects of the multiply inherited classes in the final object For example, here is another way that House could be constructed in Java: class Foundation { // } class Walls{ // }
Bar Code Generation In Java
Using Barcode creation for Java Control to generate, create barcode image in Java applications.
Printing Code 39 In Java
Using Barcode creator for Java Control to generate, create Code 3 of 9 image in Java applications.
- 655 -
Printing Code 128 In Java
Using Barcode printer for Java Control to generate, create Code 128C image in Java applications.
GS1 RSS Drawer In Java
Using Barcode printer for Java Control to generate, create GS1 DataBar Expanded image in Java applications.
class Rooms { // } /* Now, House includes Foundation, Walls, and Rooms as object members */ class House { Foundation f; Walls w; Rooms r; // } Here, Foundation, Walls, and Rooms are objects that are part of House rather than inherited by House One other point: sometimes a C++ program will contain a multiple-inheritance hierarchy simply because of poor initial design A good time to correct this type of design flaw is when you port to Java
ISBN - 13 Generation In Java
Using Barcode printer for Java Control to generate, create ISBN image in Java applications.
Encoding Barcode In Java
Using Barcode creation for BIRT reports Control to generate, create bar code image in Eclipse BIRT applications.
Destructors Versus Finalization
Painting Data Matrix 2d Barcode In Objective-C
Using Barcode printer for iPad Control to generate, create Data Matrix ECC200 image in iPad applications.
Drawing EAN / UCC - 14 In Java
Using Barcode maker for Eclipse BIRT Control to generate, create UCC-128 image in BIRT applications.
When you move from C++ to Java, one of the more subtle, yet important issues you will face is the difference between a C++ destructor and a Java finalize( ) method Although similar in many respects, their actual operation is distinctively different Let's begin by reviewing the purpose and effect of a C++ destructor and the Java finalize( ) method In C++, when an object goes out of scope, it is destroyed Just prior to its destruction, its destructor function is called (if it has one) This is a hard-and-fast rule There are no exceptions Let's look more closely at each part of this rule: Every object is destroyed when it goes out of scope Thus, if you declare a local object inside a function, when that function returns, that local object is automatically destroyed The same goes for function parameters and for objects returned by functions Just before destruction, the object's destructor is called This happens immediately, and before any other program statements will execute Thus, a C++ destructor will always execute in a deterministic fashion You can always know when and where a destructor will be executed In Java, the tight linkage of the destruction of an object and the calling of its finalize( ) method does not exist In Java, objects are not explicitly destroyed when they go out of scope Rather, an object is marked as unused when there are no longer any references pointing to it Even then, the finalize( ) method will not be called until the garbage collector runs Thus, you cannot know precisely when or where a call to finalize( ) will occur Even if you execute a call to gc( ) (the garbage collector), there is no guarantee that finalize( ) will immediately be executed While the deterministic behavior of a C++ constructor and the somewhat probabilistic aspect of finalization are of little concern in most cases, they will have an impact on others For example, consider the following C++ program: // This C++ program can call f() indefinitely #include <iostream> #include <cstdlib> using namespace std; const int MAX = 5;
UCC.EAN - 128 Generator In None
Using Barcode maker for Online Control to generate, create GTIN - 128 image in Online applications.
Bar Code Maker In VB.NET
Using Barcode drawer for VS .NET Control to generate, create barcode image in .NET framework applications.
- 656 -
Creating USS Code 128 In None
Using Barcode drawer for Microsoft Excel Control to generate, create Code 128 image in Excel applications.
Reading Code 128C In Java
Using Barcode decoder for Java Control to read, scan read, scan image in Java applications.
int count = 0; class X { public: // constructor X() { if(count<MAX) { count++; } else { cout << "Error can't construct"; exit(1); } } // destructor ~X() { count ; } }; void f() { X ob; // allocate an object // destruct on way out } int main() { int i; for(i=0; i < (MAX*2); i++) { f(); cout << "Current count is: " << count << endl;
return 0;
Here is the output generated by this program: Current Current Current Current Current Current Current Current Current Current count count count count count count count count count count is: is: is: is: is: is: is: is: is: is: 0 0 0 0 0 0 0 0 0 0
Look carefully at the constructor and destructor for X The constructor increments the value of count as long as count is less than MAX The destructor decrements count Thus, count is incremented when an X object is created and decremented when an X object is destroyed But no more than MAX objects can exist at any one time However, in main( ), f( ) is called MAX*2 times without causing an error! Here is why Inside f( ), an object of type X is created, causing count to be incremented, and then the function returns This causes the object to immediately go out of scope and its destructor to be called, which decrements count Thus, calling f( ) has no net effect on the value of count This means that it can be called indefinitely However, this is not the case when this program is converted to Java
- 657 -
Here is the Java version of the preceding program: // This Java program will fail after 5 calls to f() class X { static final int MAX = 5; static int count = 0; // constructor X() { if(count<MAX) { count++; } else { Systemoutprintln("Error can't construct"); Systemexit(1); }
// finalization protected void finalize() { count ; } static void f() { X ob = new X(); // allocate an object // destruct on way out } public static void main(String args[]) { int i; for(i=0; i < (MAX*2); i++) { f(); Systemoutprintln("Current count is: " + count); }
This program will fail after five calls to f( ), as this output shows: Current Current Current Current Current Error count count count count count can't is: 1 is: 2 is: 3 is: 4 is: 5 construct
The reason the program fails is that garbage collection does not occur each time f( ) returns Thus, finalize( ) is not invoked, and the value of count is not decremented After five calls to the method, count reaches its maximum value and the program fails It is important to emphasize that precisely when garbage collection occurs is implementation dependent It is possible that for some implementation of Java, on some platform, the preceding program will function similarly to its C++ version However, the point of the example remains: In C++, you know when and where a destructor will be called In Java, you do not know when or where finalize( ) will be executed Therefore, when porting code from C++ to Java, you will need to watch for instances in which the precise timing of the execution of a destructor is relied upon
- 658 -
Copyright © OnBarcode.com . All rights reserved.