HOW NOT TO DO IT in Java

Generation UPC Code in Java HOW NOT TO DO IT
HOW NOT TO DO IT
UPC Symbol Decoder In Java
Using Barcode Control SDK for Java Control to generate, create, read, scan barcode image in Java applications.
Removing an item from the middle of a Vector using removeElementAt(n) is achieved by copying all elements from n to the end of the array to the preceding slot. Most of the comments we have made for Vector apply to Stack. There is, however, no Stack constructor that sets its initial size, so you need to use the setSize() method inherited from Vector. A String is frequently used as a key to a Hashtable; however, as we saw in Section 7.8.3, they are not without problems and we suggested that a wrapper class that stores the hash value of the String could provide faster lookup. Integers also make useful keys because Integer.hashCode() simply returns the Integer value. Finally, think about whether an Array might provide a faster and more memory-ef cient container than a Vector or a Hashtable. Vector can be extremely slow if it is used incorrectly. In Wireless Java for Symbian Devices, an example based on a rst-in rst-out queue is given: a vector-based implementation was around 100 times slower than a reasonably optimized array-based implementation.
Generate UPC Code In Java
Using Barcode creator for Java Control to generate, create Universal Product Code version A image in Java applications.
7.10 How Not To Do It
GS1 - 12 Recognizer In Java
Using Barcode decoder for Java Control to read, scan read, scan image in Java applications.
We have discussed a number of ideas for improving the performance of our code. This section brings several of these together in an example. The following code is a slightly extreme example of how not to do it. The code goes through a company database extracting information about each employee:
Print Barcode In Java
Using Barcode generation for Java Control to generate, create barcode image in Java applications.
1 2 3 4 5 6 7 8 9 10 11 float IMP_TO_MET = 1/2.2; String nameList = ""; Vector employees = new Vector(); for(int id = 0; id < company.getNumberEmployees(); id = id+1){ nameList += company.getCompanyName() + "\t"; nameList += company.getEmployee(id).getName() + "\t"; nameList += company.getEmployee(id).getWeight() * IMP_TO_MET + "\n"; // do something with nameList nameList = ""; employees.addElement(company.getEmployee(id)); }
Recognizing Bar Code In Java
Using Barcode scanner for Java Control to read, scan read, scan image in Java applications.
Here are the problems: Line 1: IMP_TO_MET should be declared static and final (ignoring for the moment that oats are not available in CLDC 1.0, though they are available in CLDC 1.1)
Encode GTIN - 12 In C#
Using Barcode generation for VS .NET Control to generate, create GTIN - 12 image in .NET framework applications.
WRITING OPTIMIZED CODE
GS1 - 12 Generator In Visual Studio .NET
Using Barcode printer for ASP.NET Control to generate, create UPC-A image in ASP.NET applications.
Line 3: It is unnecessary to use a Vector, particularly as we can nd out the number of employees; an Array would be more appropriate; if we do need to use a Vector, we should at least specify its initial size Line 4: We should dereference company.getNumberEmployees outside the loop and use a local variable Line 4: id++ may optimize better Line 5: getCompanyName() should be de-referenced outside the loop Lines 6, 7, 10: company.getEmployee(id) should be obtained only once inside the loop Line 6, 7: Should use a StringBuffer. The following code shows how we might resolve these problems. We have de ned tab and nl as char rather than as StringBuffer: appending one StringBuffer to another is no better than appending a String to a StringBuffer, and signi cantly slower than appending a char.
Drawing Universal Product Code Version A In VS .NET
Using Barcode creation for .NET framework Control to generate, create UPC-A Supplement 5 image in VS .NET applications.
public final static float IMP_TO_MET = 1/2.2; final char tab = '\t'; final char nl = '\n'; int numberEmployees = company.getNumberEmployees(); Employee[] employees = new Employee[numberEmployees]; StringBuffer nameList = new StringBuffer(128); StringBuffer companyName = new StringBuffer(company.getCompanyName()).append(tab); for(int id = 0; id < numberEmployees; id++){ nameList.append(companyName); Employee employee = company.getEmployee(id); nameList.append(employee.getName()).append(tab); nameList.append(employee.getWeight()*IMP_TO_MET).append(nl); // Do something with nameList
UCC - 12 Drawer In Visual Basic .NET
Using Barcode encoder for .NET framework Control to generate, create UPCA image in VS .NET applications.
Finally, we reuse the StringBuffer, though note that this does not physically resize its internal store:
Print Barcode In Java
Using Barcode generation for Java Control to generate, create bar code image in Java applications.
nameList.setLength(0); employees[id] = employee; }
Printing EAN / UCC - 13 In Java
Using Barcode printer for Java Control to generate, create USS-128 image in Java applications.
COPYING AN ARRAY
Create Bar Code In Java
Using Barcode creation for Java Control to generate, create barcode image in Java applications.
7.11 Copying an Array
MSI Plessey Printer In Java
Using Barcode generator for Java Control to generate, create MSI Plessey image in Java applications.
System.arraycopy() is a standard Java method which copies the contents of one array into a second array, and is generally implemented as a native method. However, rather than JNI, it uses the native interface of the VM, which provides direct access to the array contents and type data. The following is part of a test used to compare arraycopy() with our javaCopy() method for copying an array, taken from the Microbench MIDlet:
ECC200 Creation In Visual Studio .NET
Using Barcode maker for .NET Control to generate, create ECC200 image in VS .NET applications.
... private static Object[] sourceArray = new Object[1000]; private static Object[] destinationArray = new Object[1000]; private static int size; private static void vmCopy(){ System.arraycopy(sourceArray, 0, destinationArray, 0, size); } private static void javaCopy(){ for(int i = size; --i >= 0; ){ destinationArray[i] = sourceArray[i]; } } ...
Creating Barcode In .NET
Using Barcode generator for ASP.NET Control to generate, create barcode image in ASP.NET applications.
The number of elements copied is determined by size, which is set by the user interface. javaCopy() and vmCopy() were called 3 200 000 times and the total durations compared: size (number of elements copied) Nokia 7650: arraycopy() javaCopy() Nokia 6600: arraycopy() javaCopy() 0 1 2 3 10
UPC Symbol Encoder In VS .NET
Using Barcode maker for ASP.NET Control to generate, create UPC Code image in ASP.NET applications.
Barcode Recognizer In .NET Framework
Using Barcode recognizer for .NET Control to read, scan read, scan image in Visual Studio .NET applications.
Paint Code128 In VS .NET
Using Barcode drawer for .NET Control to generate, create Code 128 image in VS .NET applications.