1: Language Fundamentals in Java

Encoding PDF 417 in Java 1: Language Fundamentals

1: Language Fundamentals
PDF 417 Reader In Java
Using Barcode Control SDK for Java Control to generate, create, read, scan barcode image in Java applications.
PDF 417 Creator In Java
Using Barcode creation for Java Control to generate, create PDF-417 2d barcode image in Java applications.
// Not OK; GolfClub does not implement Sporty // I don't care what anyone says } }
Read PDF 417 In Java
Using Barcode reader for Java Control to read, scan read, scan image in Java applications.
Bar Code Generator In Java
Using Barcode printer for Java Control to generate, create bar code image in Java applications.
The bottom line is this: any object that passes the IS-A test for the declared array type can be assigned to an element of that array.
Recognizing Barcode In Java
Using Barcode reader for Java Control to read, scan read, scan image in Java applications.
Making PDF-417 2d Barcode In Visual C#
Using Barcode drawer for Visual Studio .NET Control to generate, create PDF417 image in VS .NET applications.
Array Reference Assignments for One-Dimensional Arrays
Painting PDF-417 2d Barcode In .NET Framework
Using Barcode generator for ASP.NET Control to generate, create PDF 417 image in ASP.NET applications.
Drawing PDF 417 In VS .NET
Using Barcode creation for VS .NET Control to generate, create PDF-417 2d barcode image in Visual Studio .NET applications.
For the exam, you need to recognize legal and illegal assignments for array reference variables. We re not talking about references in the array (in other words, array elements), but rather references to the array object. For example, if you declare an int array, the reference variable you declared can be reassigned to any int array (of any size), but cannot be reassigned to anything that is not an int array, including an int value. Remember, all arrays are objects, so an int array reference cannot refer to an int primitive. The following code demonstrates legal and illegal assignments for primitive arrays:
PDF-417 2d Barcode Maker In Visual Basic .NET
Using Barcode encoder for .NET framework Control to generate, create PDF417 image in .NET applications.
Creating Data Matrix In Java
Using Barcode encoder for Java Control to generate, create DataMatrix image in Java applications.
int[] splats; int[] dats = new int[4]; char[] letters = new char[5]; splats = dats; // OK, dats refers to an int array splats = letters; // NOT OK, letters refers to a char array
EAN / UCC - 14 Creation In Java
Using Barcode creator for Java Control to generate, create EAN 128 image in Java applications.
Matrix 2D Barcode Maker In Java
Using Barcode printer for Java Control to generate, create Matrix Barcode image in Java applications.
It s tempting to assume that because a variable of type byte, short, or char can be explicitly promoted and assigned to an int, an array of any of those types could be assigned to an int array. You can t do that in Java, but it would be just like those cruel, heartless (but otherwise attractive) exam developers to put tricky array assignment questions in the exam. Arrays that hold object references, as opposed to primitives, aren t as restrictive. Just as you can put a Honda object in a Car array (because Honda extends Car), you can assign an array of type Honda to a Car array reference variable as follows:
4-State Customer Barcode Generator In Java
Using Barcode generation for Java Control to generate, create OneCode image in Java applications.
Painting EAN 13 In None
Using Barcode creator for Microsoft Excel Control to generate, create EAN13 image in Office Excel applications.
Car[] cars; Honda[] cuteCars = new Honda[5]; cars = cuteCars; // OK because Honda is a type of Car Beer[] beers = new Beer [99]; cars = beers; // NOT OK, Beer is not a type of Car
Generate Code 39 Full ASCII In VB.NET
Using Barcode maker for VS .NET Control to generate, create Code 39 image in .NET framework applications.
2D Barcode Drawer In Visual Basic .NET
Using Barcode generator for Visual Studio .NET Control to generate, create Matrix 2D Barcode image in .NET framework applications.
Apply the IS-A test to help sort the legal from the illegal. Honda IS-A Car, so a Honda array can be assigned to a Car array. Beer IS-A Car is not true; Beer does not extend Car (not to mention the fact that it doesn t make logical sense, unless you ve already had too much of it).
Bar Code Drawer In Visual Basic .NET
Using Barcode creation for VS .NET Control to generate, create bar code image in VS .NET applications.
EAN13 Generation In VS .NET
Using Barcode generation for ASP.NET Control to generate, create UPC - 13 image in ASP.NET applications.
Array Declaration, Construction, and Initialization (Exam Objective 1.1)
Code 128 Code Set C Decoder In Visual Basic .NET
Using Barcode reader for .NET Control to read, scan read, scan image in Visual Studio .NET applications.
Create Bar Code In .NET
Using Barcode generation for Visual Studio .NET Control to generate, create bar code image in Visual Studio .NET applications.
You cannot reverse the legal assignments. A Car array cannot be assigned to a Honda array. A Car is not necessarily a Honda, so if you ve declared a Honda array, it might blow up if you were allowed to assign a Car array to the Honda reference variable. Think about it: a Car array could hold a reference to a Ferrari, so someone who thinks they have an array of Hondas could suddenly find themselves with a Ferrari. Remember that the IS-A test can be checked in code using the instanceof operator. The instanceof operator is covered in more detail in 3. Figure 1-7 shows an example of legal and illegal assignments for references to an array.
FIGURE 1-6
Legal and illegal array assignments
1: Language Fundamentals
The rules for array assignment apply to interfaces as well as classes. An array declared as an interface type can reference an array of any type that implements the interface. Remember, any object from a class implementing a particular interface will pass the IS-A (instanceof) test for that interface. For example, if Box implements Foldable, the following is legal:
Foldable[] foldingThings; Box[] boxThings = new Box[3]; foldingThings = boxThings; // OK, Box implements Foldable, so Box IS-A Foldable
Array Reference Assignments for Multidimensional Arrays
When you assign an array to a previously declared array reference, the array you re assigning must be the same dimension as the reference you re assigning it to. For example, a two-dimensional array of int arrays cannot be assigned to a regular int array reference, as follows:
int[] blots; int[][] squeegees = new int[3][]; blots = squeegees; // NOT OK, squeegees is a two-d array of int arrays int[] blocks = new int[6]; blots = blocks; // OK, blocks is an int array
Pay particular attention to array assignments using different dimensions. You might, for example, be asked if it s legal to assign an int array to the first element in an array of int arrays, as follows:
int[][] books = new int[3][]; int[] numbers = new int[6]; int aNumber = 7; books[0] = aNumber; //NOT OK, expecting an int array instead of an int books[0] = numbers; //OK, numbers is an int array
Copyright © OnBarcode.com . All rights reserved.