visual basic barcode printing 7: Objects and Collections in Java

Creating PDF 417 in Java 7: Objects and Collections

7: Objects and Collections
PDF-417 2d Barcode Decoder In Java
Using Barcode Control SDK for Java Control to generate, create, read, scan barcode image in Java applications.
Create PDF-417 2d Barcode In Java
Using Barcode printer for Java Control to generate, create PDF 417 image in Java applications.
between legal, appropriate, and efficient hashcoding. We also saw that even though wildly inefficient, it s legal for a hashCode() method to always return the same value. Next we turned to collections, where we learned about Lists, Sets, and Maps, and the difference between ordered and sorted collections. We learned the key attributes of the common collection classes, and when to use which. Finally, we dove into garbage collection, Java s automatic memory management feature. We learned that the heap is where objects live and where all the cool garbage collection activity takes place. We learned that in the end, the JVM will perform garbage collection whenever it wants to. You (the programmer) can request a garbage collection run, but you can t force it. We talked about garbage collection only applying to objects that are eligible, and that eligible means inaccessible from any live thread. Finally, we discussed the rarely useful finalize() method, and what you ll have to know about it for the exam. All in all one fascinating chapter.
Decoding PDF-417 2d Barcode In Java
Using Barcode reader for Java Control to read, scan read, scan image in Java applications.
Painting Bar Code In Java
Using Barcode creation for Java Control to generate, create barcode image in Java applications.
Two-Minute Drill
Decode Bar Code In Java
Using Barcode reader for Java Control to read, scan read, scan image in Java applications.
Make PDF 417 In Visual C#
Using Barcode printer for .NET Control to generate, create PDF417 image in .NET applications.
TWO-MINUTE DRILL
Generating PDF417 In .NET
Using Barcode encoder for ASP.NET Control to generate, create PDF-417 2d barcode image in ASP.NET applications.
Creating PDF-417 2d Barcode In .NET
Using Barcode drawer for .NET framework Control to generate, create PDF 417 image in Visual Studio .NET applications.
Here are some of the key points from 7.
Make PDF-417 2d Barcode In Visual Basic .NET
Using Barcode drawer for .NET framework Control to generate, create PDF417 image in Visual Studio .NET applications.
Make UCC-128 In Java
Using Barcode encoder for Java Control to generate, create EAN128 image in Java applications.
Overriding hashCode() and equals() The critical methods in class Object are equals(), finalize(),
Barcode Printer In Java
Using Barcode generator for Java Control to generate, create barcode image in Java applications.
Paint GS1 DataBar Limited In Java
Using Barcode drawer for Java Control to generate, create GS1 DataBar image in Java applications.
hashCode(), and toString().
Paint Code 93 Full ASCII In Java
Using Barcode printer for Java Control to generate, create Uniform Symbology Specification Code 93 image in Java applications.
Painting Code-39 In .NET Framework
Using Barcode drawer for Reporting Service Control to generate, create USS Code 39 image in Reporting Service applications.
equals(), hashCode(), and toString() are public (finalize()
Create Barcode In None
Using Barcode encoder for Office Excel Control to generate, create bar code image in Microsoft Excel applications.
Drawing Bar Code In None
Using Barcode drawer for Font Control to generate, create bar code image in Font applications.
is protected).
DataMatrix Maker In None
Using Barcode maker for Font Control to generate, create Data Matrix 2d barcode image in Font applications.
GS1 - 13 Generation In Java
Using Barcode creation for Android Control to generate, create EAN-13 image in Android applications.
Fun facts about toString(): Override toString() so that System.out.println() or other
EAN128 Reader In Visual C#
Using Barcode decoder for Visual Studio .NET Control to read, scan read, scan image in .NET applications.
Encode ANSI/AIM Code 39 In Objective-C
Using Barcode printer for iPad Control to generate, create Code 39 Full ASCII image in iPad applications.
methods can see something useful.
Override toString() to return the essence of your object s state. Use == to determine if two reference variables refer to the same object. Use equals() to determine if two objects are meaningfully equivalent. If you don t override equals(), your objects won t be useful hashtable/
hashmap keys.
If you don t override equals(), two different objects can t be considered
the same.
Strings and wrappers override equals() and make good hashtable/
hashmap keys.
When overriding equals(), use the instanceof operator to be sure
you re evaluating an appropriate class.
When overriding equals(), compare the objects significant attributes. Highlights of the equals() contract: Reflexive: x.equals(x) is true. Symmetric: If x.equals(y) is true, then y.equals(x) must
be true.
Transitive: If x.equals(y) is true, and y.equals(z) is true,
then z.equals(x) is true.
7: Objects and Collections
Consistent: Multiple calls to x.equals(y) will return the same result. Null: If x is not null, then x.equals(null) is false. If x.equals(y) is true, then x.hashCode() == y.hashCode()
must be true.
If you override equals(), override hashCode(). Classes HashMap, Hashtable, LinkedHashMap, and LinkedHashSet
use hashing.
A legal hashCode() override compiles and runs. An appropriate hashCode() override sticks to the contract. An efficient hashCode() override distributes keys randomly across
a wide range of buckets.
To reiterate: if two objects are equal, their hashcodes must be equal. It s legal for a hashCode() method to return the same value for all instances
(although in practice it s very inefficient).
Highlights of the hashCode() contract: Consistent: Multiple calls to x.hashCode() return the same integer. If x.equals(y) is true, then x.hashCode() == y.hashCode()
must be true.
If x.equals(y) is false, then x.hashCode() ==
y.hashCode() can be either true or false, but false will tend to create better efficiency.
Transient variables aren t appropriate for equals() and hashCode(). Collections Common collection activities include adding objects, removing objects, verifying
object inclusion, retrieving objects, and iterating.
Three meanings for collection : collection Represents the data structure in which objects are stored Collection java.util.Collection Interface from which Set
and List extend
Collections A class that holds static collection utility methods
Two-Minute Drill
Three basic flavors of collections include Lists, Sets, Maps: Lists of things: Ordered, duplicates allowed, with an index Sets of things: May or may not be ordered and/or sorted, duplicates
not allowed
Maps of things with keys: May or may not be ordered and/or sorted,
duplicate keys not allowed
Four basic subflavors of collections include Sorted, Unsorted, Ordered,
Unordered.
Ordered means iterating through a collection in a specific, nonrandom order. Sorted means iterating through a collection in a natural sorted order. Natural means alphabetic, numeric, or programmer-defined, whichever applies. Key attributes of common collection classes: ArrayList: Fast iteration and fast random access Vector: Like a somewhat slower ArrayList, mainly due to its synchronized
methods
LinkedList: Good for adding elements to the ends, i.e., stacks and queues HashSet: Assures no duplicates, provides no ordering LinkedHashSet: No duplicates; iterates by insertion order or last accessed
(new with 1.4)
TreeSet: No duplicates; iterates in natural sorted order HashMap: Fastest updates (key/value pairs); allows one null key,
Copyright © OnBarcode.com . All rights reserved.