Object Initialization: good practice?

I got a small doubt while i was doing some work: if fields in a class are objects, should they be initialized as soon as declared or should they be initialized in the constructor?.
for example
class MyClass{
Object obj = new Object();
or
class MyClass{
Object obj;
public MyClass(){
obj = new Object();
I prefer the first,specially if there is no complexity in the constructors of either "Object" or "MyClass" because there is no way any method will deal with an uninitialized obj.
Which one should be done, and why?
Regards,

I prefer the first,specially if there is no complexity in the constructors of either "Object" or "MyClass" because there is no way any method will deal with an uninitialized obj.That last phrase is the key. You are absolutely correct on that, but it's entirely possible to manage it with all initialization being done in the ctor.
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Similar Messages

Is it necessary to use this. on objects or is it just good practice?

Is it necessary to use this. on objects or is it just good practice?

warnerja wrote:
yawmark wrote:
Is it necessary to use this. on objects or is it just good practice?It's good practice to use it when it's necessary.
~No, it's only necessary to use it when it's necessary.
It's good practice to use it when it's good practice.<****/>
<****/>
<****/>
(the sound of one hand, clapping)

Good practice to initalize all instance variables with type String to emptr

Is it a good practice to initalize all instance variables with
type String to emptry string?
#1 approach:
public class A
{ private String name = "";
private String address ="";
//etc...
rather than
#2 approach:
public class A
{ private String name;
private String address;
//etc...
When I read Java books, the examples don't usually do #1 approach.
The problem is if we don't initialize to empty string, when we call
the getter method of that instance variable, it will return null.
Please advise. Thanks!!

Please advise. Thanks!!It depends on your coding style. If you can avoid lots of checks for null Strings in the rest of the code then why not initialize to "".
You have the same situation when a method returns an array. If you under circumstances return a null array reference then you have to always check for this special case, but if you return a zero length array instead you have no special case. All loops will just run 0 iterations and everything will work fine.
So in general I guess the return of zero objects instead of null references really boils down to whether it simplicates the rest of your code by removing lots of extra checks for the special null case. This usage is especially favourable in the zero length array case. See Effective Java by Bloch, item 27.

Initialization Blocks -- Practical Example.

I am curious about I topic that I have just recently learned about and would like to post it for discussion.
Does anyone know of a practical example of the use of an initialization block? Why would one want to use an initialization block? What can be accomplished with an initialization block that you cannot accomplish with a constructor that doesn't accept any parameters?

Hi Robert,
Initializers are used in initialization of object and classes. They can also be used to define constants in Interfaces.
Here I am explaning by corelating the Constructor with Initialization.
In what order is initialization code executed? What should I put where ?
Instance variable initialization code can go in three places within a class:
In an instance variable initializer for a class (or a superclass).
class C {
String var = "val";
In a constructor for a class (or a superclass).
public C() { var = "val"; }
In an object initializer block. This is new in Java 1.1; its just like a static initializer block but without the keyword static.
{ var = "val"; }
The order of evaluation (ignoring out of memory problems) when you say new C() is:
1.Call a constructor for C's superclass (unless C is Object, in which case it has no superclass). It will always be the no-argument constructor, unless the programmer explicitly coded super(...) as
the very first statement of the constructor.
2.Once the super constructor has returned, execute any instance variable initializers and object initializer blocks in textual (left-to-right) order. Don't be confused by the fact that javadoc and
javap use alphabetical ordering; that's not important here.
3.Now execute the remainder of the body for the constructor. This can set instance variables or do anything else.
In general, you have a lot of freedom to choose any of these three forms. My recommendation is to use instance variable initailizers in cases where there is a variable that takes the same value
regardless of which constructor is used. Use object initializer blocks only when initialization is complex (e.g. it requires a loop) and you don't want to repeat it in multiple constructors. Use a constructor
for the rest.
Here's another example:
Program:
class A {
String a1 = ABC.echo(" 1: a1");
String a2 = ABC.echo(" 2: a2");
public A() {ABC.echo(" 3: A()");}
class B extends A {
String b1 = ABC.echo(" 4: b1");
String b2;
public B() {
ABC.echo(" 5: B()");
b1 = ABC.echo(" 6: b1 reset");
a2 = ABC.echo(" 7: a2 reset");
class C extends B {
String c1;
{ c1 = ABC.echo(" 8: c1"); }
String c2;
String c3 = ABC.echo(" 9: c3");
public C() {
ABC.echo("10: C()");
c2 = ABC.echo("11: c2");
b2 = ABC.echo("12: b2");
public class ABC {
static String echo(String arg) {
System.out.println(arg);
return arg;
public static void main(String[] args) {
new C();
Output:
1: a1
2: a2
3: A()
4: b1
5: B()
6: b1 reset
7: a2 reset
8: c1
9: c3
10: C()
11: c2
12: b2
When should I use constructors, and when should I use other methods?
The glib answer is to use constructors when you want a new object; that's what the keyword new is for. The infrequent answer is that constructors are often over-used, both in when they are called and
in how much they have to do. Here are some points to consider
Modifiers: As we saw in the previous question, one can go overboard in providing too many constructors. It is usually better to minimize the number of constructors, and then provide modifier
methods, that do the rest of the initialization. If the modifiers return this, then you can create a useful object in one expression; if not, you will need to use a series of statements. Modifiers are
good because often the changes you want to make during construction are also changes you will want to make later, so why duplicate code between constructors and methods.
Factories: Often you want to create something that is an instance of some class or interface, but you either don't care exactly which subclass to create, or you want to defer that decision to
runtime. For example, if you are writing a calculator applet, you might wish that you could call new Number(string), and have this return a Double if string is in floating point format, or a Long if
string is in integer format. But you can't do that for two reasons: Number is an abstract class, so you can't invoke its constructor directly, and any call to a constructor must return a new instance
of that class directly, not of a subclass. A method which returns objects like a constructor but that has more freedom in how the object is made (and what type it is) is called a factory. Java has no
built-in support or conventions for factories, but you will want to invent conventions for using them in your code.
Caching and Recycling: A constructor must create a new object. But creating a new object is a fairly expensive operation. Just as in the real world, you can avoid costly garbage collection by
recycling. For example, new Boolean(x) creates a new Boolean, but you should almost always use instead (x ? Boolean.TRUE : Boolean.FALSE), which recycles an existing value rather than
wastefully creating a new one. Java would have been better off if it advertised a method that did just this, rather than advertising the constructor. Boolean is just one example; you should also
consider recycling of other immutable classes, including Character, Integer, and perhaps many of your own classes. Below is an example of a recycling factory for Numbers. If I had my choice, I
would call this Number.make, but of course I can't add methods to the Number class, so it will have to go somewhere else.
public Number numberFactory(String str) throws NumberFormatException {
try {
long l = Long.parseLong(str);
if (l >= 0 && l < cachedLongs.length) {
int i = (int)l;
if (cachedLongs[i] != null) return cachedLongs;
else return cachedLongs[i] = new Long(str);
} else {
return new Long(l);
} catch (NumberFormatException e) {
double d = Double.parseDouble(str);
return d == 0.0 ? ZERO : d == 1.0 ? ONE : new Double(d);
private Long[] cachedLongs = new Long[100];
private Double ZERO = new Double(0.0);
private Double ONE = new Double(1.0);
We see that new is a useful convention, but that factories and recycling are also useful. Java chose to support only new because it is the simplest possibility, and the Java philosophy is to keep the
language itself as simple as possible. But that doesn't mean your class libraries need to stick to the lowest denominator. (And it shouldn't have meant that the built-in libraries stuck to it, but alas, they
did.)
I have a class with six instance variables, each of which could be initialized or not. Should I write 64 constructors?
Of course you don't need (26) constructors. Let's say you have a class C defined as follows:
public class C { int a,b,c,d,e,f; }
Here are some things you can do for constructors:
1.Guess at what combinations of variables will likely be wanted, and provide constructors for those combinations. Pro: That's how it's usually done. Con: Difficult to guess correctly; lots of
redundant code to write.
2.Define setters that can be cascaded because they return this. That is, define a setter for each instance variable, then use them after a call to the default constructor:
public C setA(int val) { a = val; return this; }
new C().setA(1).setC(3).setE(5);
Pro: This is a reasonably simple and efficient approach. A similar idea is discussed by Bjarne Stroustrop on page 156 of The Design and Evolution of C++. Con: You need to write all the little
setters, they aren't JavaBean-compliant (since they return this, not void), they don't work if there are interactions between two values.
3.Use the default constructor for an anonymous sub-class with a non-static initializer:
new C() {{ a = 1; c = 3; e = 5; }}
Pro: Very concise; no mess with setters. Con: The instance variables can't be private, you have the overhead of a sub-class, your object won't actually have C as its class (although it will still be an
instanceof C), it only works if you have accessible instance variables, and many people, including experienced Java programmers, won't understand it. Actually, its quite simple: You are defining a
new, unnamed (anonymous) subclass of C, with no new methods or variables, but with an initialization block that initializes a, c, and e. Along with defining this class, you are also making an
instance. When I showed this to Guy Steele, he said "heh, heh! That's pretty cute, all right, but I'm not sure I would advocate widespread use..."
4.You can switch to a language that directly supports this idiom.. For example, C++ has optional arguments. So you can do this:
class C {
public: C(int a=1, int b=2, int c=3, int d=4, int e=5);
new C(10);
Common Lisp has keyword arguments as well as optional arguments, so you can do this:
(defstruct C a b c d e f) ; Defines the class
(make-C :a 1 :c 3 :e 5) ; Construct an
instance
What about class initialization?
It is important to distinguish class initialization from instance creation. An instance is created when you call a constructor with new. A class C is initialized the first time it is actively used. At that time,
the initialization code for the class is run, in textual order. There are two kinds of class initialization code: static initializer blocks (static { ... }), and class variable initializers (static String var =
Active use is defined as the first time you do any one of the following:
1.Create an instance of C by calling a constructor;
2.Call a static method that is defined in C (not inherited);
3.Assign or access a static variable that is declared (not inherited) in C. It does not count if the static variable is initialized with a constant expression (one involving only primitive operators (like +
or ||), literals, and static final variables), because these are initialized at compile time.
Here is an example:
Program:
class A {
static String a1 = ABC.echo(" 1: a1");
static String a2 = ABC.echo(" 2: a2");
class B extends A {
static String b1 = ABC.echo(" 3: b1");
static String b2;
static {
ABC.echo(" 4: B()");
b1 = ABC.echo(" 5: b1 reset");
a2 = ABC.echo(" 6: a2 reset");
class C extends B {
static String c1;
static { c1 = ABC.echo(" 7: c1"); }
static String c2;
static String c3 = ABC.echo(" 8: c3");
static {
ABC.echo(" 9: C()");
c2 = ABC.echo("10: c2");
b2 = ABC.echo("11: b2");
public class ABC {
static String echo(String arg) {
System.out.println(arg);
return arg;
public static void main(String[] args) {
new C();
Output:
1: a1
2: a2
3: b1
4: B()
5: b1 reset
6: a2 reset
7: c1
8: c3
9: C()
10: c2
11: b2
I hope the above will help you.
Thanks
Bakrudeen

What is a good practice to handle LOV in jdev apps?

Hi, experts,
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refcode(id, low_value,high_value,meaning,domain_no),
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In the end user's UI, the code/number field values should be displayed by a meaning word from refcode,
To accomplish this goal, I will create numberous associations between different tables with refcode,
and create VOs to have refcode entity view as a secondary entity view.
I feel some odd in doing so(because so many associations with the same refcode table),
Is that a good practice to handle LOV this way ?
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On Fusion Developer's Guide for Oracle Application Development Framework
10.3 Defining a Base View Object for Use with Lookup Tables
(http://docs.oracle.com/cd/E37975_01/web.111240/e16182/bclookups.htm#BABIBHIJ)
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There are valuable information and suggestions on implement lookup features, especially by using view criteria
(the View Criteria and View accessor is one of important and great idea in ADF)
I think, by using of view criteria, the derivative attribute to display fk information can be implemented in a convinent way without FK associations definition.

Overloaded methods-yes or no & is this a good practice

say i have two methods with the same name that take in the same parameters and have the same return type. the difference between the two is that one is static while the other is not. Also the methods contain different codes.
are the methods going to function normally when i use em? also if they do function normally, is this essentially a good practice?
if code is needed to answer this, please do mention it and i will think of a mini scenario where this can be applied and write a small piece of code for that.
thanx. help will be appreciated.

avi.cool wrote:
duffymo wrote:
each account has its own password that the user sets when the account is created-this password is declared as a state variable in the class file. One password per account? A bad model, IMO. My on-line banking software associates credentials with me, not my accounts. I see several accounts when I log in, and I don't have to log in individually for each one.
besides that, theres also a bank password-this is declared and initialized as a static state variable in the class file. some of the operations require the bank password for access while others require account password.Static bank password? I'm very glad this is a throw-away student exercise, because you have no idea what you're doing.hahaaa, tru tru, its for a skool assignment for my first ever programming course. though not a throw away, i putting a lot of work into this :-) i m not actually trying to resolve any security issues here or strengthen account security. basically, I am only trying to exhibit a tiny bit of creativity while showing understanding of course contents. so nothing to stress on :-D i know not very creative but its all i got at this stage.
i was trying to exhibit the use of overloaded methods in my program by having method to check the password that the user enters to access operations.
now the ones that require account password, i was thinking of having the password check method as a non-static method since its associated with the object.
while the ones that need bank password, i wanted to have as static method.
i wanted both methods to have the same name.You've no idea what you're doing.
how i solved it,
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Its exactly what I told you.. but now, you just have to come on here and post this :p
and isn't this sort of like cheating? :P I mean this IS our exam you know... You're basically asking other for the arithmetic and logic lol.

Is it the good practice?

Hi,
With OIM 11g, I try to implement different UI requests for user creation.
A request for external users and a request for internal users.
For both of them, UI displays only :
-Last name
-First name
-Birth Date
For external user request, email is generated by firstname an lastname and prefixed by external.
For internal user request, email is generated by firstname an lastname and not prefixed.
To do that, I would like to use the request API "Platform.getService(RequestService.class)" in an event handler to get the request template name and generate the mail according to the template name.
Can I get the request id in the event handler?
Is it the good practice?
Regards,
Pierre.

user1214565 wrote:
thank you very much bbagaria,
Can I use different datasets for user creation, one for external user, one for internal (I thought I could only modify and use the default dataset: /metadata/iam-features-requestactions/model-data/CreateUserDataSet.xml for all creation request)?
If yes, how? (I tried to import MyCreateInternalUserDataSet.xml but it didn't work)
With the default dataset, I expected to create two request templates, one for internal and one for external and get the template name in the a preprocess event handler.
Regards,
PierrePierre,
I would suggest that you just modify the CreateUserDataSet.xml (not rename but import it back at same location in MDS [over-write]) to add additional field for type of user (hidden if you want) and use prepopulate with the type of user internal or external based on the template selection. The prepopulate adapter takes in RequestData object and that has getRequestTemplateName() method. Or just populate the email based on the template selection.
I haven't tried this but theoretically it seems that you can user this.
http://download.oracle.com/docs/cd/E17904_01/apirefs.1111/e17334/oracle/iam/request/vo/RequestData.html#getRequestTemplateName__
HTH,
BB

Good practices for ECC 6.0 wr.t. internal tables..

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wa-field2 = '2'.
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Regards,
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Is a good practice store pages into ECM ?

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My team is building a portal that will be composed by a template/skin and some static pages. We think to put this pages into ECM, there is a good practice? How could i internacionalizate ?
Thanks you.

Why you need to store html pages in ECM ?Is it really required?
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you can manage simply by calling JSTL with EL and UCM mix to achieve it.But again it is simple form.
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Good practices with GUI? (deriving classes)

Hello!
I wonder if it is good practice to have the GUI in the
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I am missing these guidelines in the tutorial, they don't tend to stress it, even though I think it is important for us newbies.

hi,
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Another point you have to see is the object-oriented view on things:
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Apex version control: what are "good practices"?

I have made my first Apex application that is been tested right now. Once this version is released, I should want to have a stable and robust versioning system for this application. I don't have any experience with this. So any info about this issue would be very welcome. Are there some good practice rules I should follow? What are things to watch out for? Etc... Some things I'd like to be able to do:
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3. Rollback to a previous version of the application
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I also would like the same for the database schema.
Any help would be very welcome...

Here how I do it:
Each Apex application has a unique version number in the format Major Release Number / Minor Release Number / Patch Release Number e.g.
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Each Release on CD is also given a unique sequential number so that different releases of the same version can be tracked through test. Each CD Release will usually consist of an application export, object scripts and a build script. The CD image is also checked into the CMDB.
If an application is going to distributed as a packaged application or installed on multiple environments then each release is a full build. For single instances, the builds are incremental.
Cheers
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Is VHDX for data drive considered good practice on a client PC?

Hi!
I don't like putting user's data files (documents, etc.) inside the user's Documents directory on C:. Instead I prefer having them on a D: disk, separate from the OS. On the other hand I don't want to create a fixed size partition as I consider it a waste
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Thanks in advance for any help.
Best regards,
Anguel

Hi,
Since the VHDX is created on C which should be the system partition, I don’t think it is more safety than separate partition.
Please consider that once the system corrupted and we have to format the C to reinstall the System, it may be difficult for us to recovery the date. But the separated partition will be easily stayed without changes.
You can try to shrink the C volume in Disk management to create a new partition.
Just my thought.
Kate Li
TechNet Community Support

JTable: RFC on good practice (SQL queries from cell editor)

I usually add/remove/edit JTable data from an external panel. But in this scenario, my client would like to be able to click on the first column of an empty row and enter a product number. Within the cell editor, I must make an SQL query to the database in order to determine if the product number is valid and if so, use part of the SQL data to populate other cells of the current row (like product description).
My problem is that this just doesn't seem right! Isn't the cell editor executed on the only Swing thread? Also, if the product number is not valid, I correctly implement the stopCellEditing() method but for some reason, you can still navigate the table (click on any other cell or press the TAB key, etc)... weird!!
Does anyone have a good practice on how to perform the SQL query in a better place and force a cell to be selected until you enter a valid number or press the CANCEL key?
I was looking at implementing the TableModelListener's tableChanged(...) method but I'm not sure if that would be a better place either.
I personally would edit outside of the table, but good practice seems hard when the requirement is to edit from a cell editor!!
Any suggestion would be greatly appreciated!
Thanks!

maybe you could write an input verifier for the column that does the query and rejects invalid entries.
maybe you could send the query off in a worker thread.
as far as making the table so you can't select any cells, hmm. not sure.
you could disable
.setEnabled(false);the table until the query comes back, something like that.

Hi i need one object from goods receipt, and one from invoice

hi gurus
what are the tables and fields we have in goods receipt and invoice
plz send one object on goods receipt
and one object on invoice
thank oyu
regards
kals.

Check EKBE table.
If BEWTP='E' means Goods Receipt and 'Q' means Invoice Receipt.
DMBTR and WRBTR fields gives you the value of that item.
ALso check this thread.
Goods Receipt and Invoice Amount
Check this thread for goods receipt notice sample program.
grn report(goods receipt notice)

Is that a good practice to use syncronize methods for application scope cls

Is that a good practice to use synchronize method in a application scope class, so I have a doubt, there a is class A, it has application scope and it contains a synchronized method add, so because of some network traffic or any unexpected exception client1 got stuck in the method, will that add method available for any other client...?
Edited by: navaneeth.j on Dec 17, 2009 4:02 AM
Edited by: navaneeth.j on Dec 17, 2009 4:04 AM

If it needs synchronization, then it probably doesn't belong in the application scope. Either keep it as is, or reconsider the scope, or make it static.

Object Initialization: good practice?

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