visual basic barcode printing The equals() Contract in Java

Encoder PDF417 in Java The equals() Contract

The equals() Contract
Read PDF 417 In Java
Using Barcode Control SDK for Java Control to generate, create, read, scan barcode image in Java applications.
PDF417 Printer In Java
Using Barcode creation for Java Control to generate, create PDF 417 image in Java applications.
Pulled straight from the Java docs, the equals() contract says:
Scan PDF 417 In Java
Using Barcode recognizer for Java Control to read, scan read, scan image in Java applications.
Create Bar Code In Java
Using Barcode maker for Java Control to generate, create bar code image in Java applications.
It is reflexive: For any reference value x, x.equals(x) should return true. It is symmetric: For any reference values x and y, x.equals(y) should
Scan Bar Code In Java
Using Barcode decoder for Java Control to read, scan read, scan image in Java applications.
PDF-417 2d Barcode Generator In C#
Using Barcode generation for VS .NET Control to generate, create PDF-417 2d barcode image in .NET applications.
return true if and only if y.equals(x) returns true.
PDF 417 Drawer In VS .NET
Using Barcode generator for ASP.NET Control to generate, create PDF 417 image in ASP.NET applications.
Generating PDF 417 In VS .NET
Using Barcode generation for .NET Control to generate, create PDF 417 image in .NET framework applications.
It is transitive: For any reference values x, y, and z, if x.equals(y) returns
Create PDF417 In VB.NET
Using Barcode drawer for VS .NET Control to generate, create PDF417 image in .NET framework applications.
Draw Data Matrix ECC200 In Java
Using Barcode encoder for Java Control to generate, create Data Matrix ECC200 image in Java applications.
true and y.equals(z) returns true, then x.equals(z) should return true.
Code 39 Full ASCII Printer In Java
Using Barcode creator for Java Control to generate, create Code39 image in Java applications.
Matrix 2D Barcode Maker In Java
Using Barcode maker for Java Control to generate, create 2D Barcode image in Java applications.
It is consistent: For any reference values x and y, multiple invocations of
USPS Confirm Service Barcode Printer In Java
Using Barcode creation for Java Control to generate, create USPS PLANET Barcode image in Java applications.
Encoding GTIN - 12 In Visual Basic .NET
Using Barcode maker for .NET framework Control to generate, create UPC Symbol image in Visual Studio .NET applications.
x.equals(y) consistently return true or consistently return false, provided no information used in equals comparisons on the object is modified.
EAN13 Encoder In C#.NET
Using Barcode generator for .NET Control to generate, create GS1 - 13 image in .NET applications.
Create Barcode In .NET Framework
Using Barcode generation for ASP.NET Control to generate, create bar code image in ASP.NET applications.
For any nonnull reference value x, x.equals(null) should return false.
Draw Code 128B In None
Using Barcode generator for Online Control to generate, create Code-128 image in Online applications.
Code 39 Extended Encoder In None
Using Barcode drawer for Online Control to generate, create Code 39 Full ASCII image in Online applications.
And you re so not off the hook yet. We haven t looked at the hashCode() method, but equals() and hashCode() are bound together by a joint contract that specifies if two objects are considered equal using the equals() method, then they must have identical hashcode values. So to be truly safe, your rule of thumb should be if you override equals(), override hashCode() as well. So let s switch over to hashCode() and see how that method ties in to equals().
Barcode Reader In Java
Using Barcode Control SDK for BIRT Control to generate, create, read, scan barcode image in BIRT reports applications.
Making Bar Code In None
Using Barcode creator for Font Control to generate, create bar code image in Font applications.
Overriding hashCode()
The hashcode value of an object is used by some collection classes (we ll look at the collections later in this chapter). Although you can think of it as kind of an object ID number, it isn t necessarily unique. Collections such as HashMap and HashSet use the hashcode value of an object to determine where the object should be stored in the collection, and the hashcode is used again to help locate the object in the collection. For the exam you do not need to understand the deep details of how the collection classes that use hashing are implemented, but you do need to know which collections use them (but, um, they all have hash in the name so you should be good
7: Objects and Collections
there). You must also be able to recognize an appropriate or correct implementation of hashCode(). This does not mean legal and does not even mean efficient. It s perfectly legal to have a terribly inefficient hashcode method in your class, as long as it doesn t violate the contract specified in the Object class documentation (we ll look at that contract in a moment). So for the exam, if you re asked to pick out an appropriate or correct use of hashcode, don t mistake appropriate for legal or efficient.
Understanding Hashcodes
In order to understand what s appropriate and correct, we have to look at how some of the collections use hashcodes. Imagine a set of buckets lined up on the floor. Someone hands you a piece of paper with a name on it. You take the name and calculate an integer code from it by using A is 1, B is 2, etc., and adding the numeric values of all the letters in the name together. A specific name will always result in the same code; for example, see Figure 7-1. We don t introduce anything random, we simply have an algorithm that will always run the same way given a specific input, so the output will always be identical for any two identical inputs. So far so good Now the way you use that code (and we ll call it a hashcode now) is to determine which bucket to place the piece of paper into (imagine that each bucket represents a different code number you might get). Now imagine that someone comes up and shows you a name and says, Please retrieve the piece of paper that matches this name. So you look at the name they show you, and run the same hashcode-generating algorithm. The hashcode tells you in which bucket you should look to find the name. You might have noticed a little flaw in our system, though. Two different names might result in the same value. For example, the names Amy and May have the same
FIGURE 7-1
Copyright © OnBarcode.com . All rights reserved.