Confused about passing by reference and passing by valule

Hi,
I am confuse about passing by reference and passing
by value. I though objects are always passed by
reference. But I find out that its true for
java.sql.PreparedStatement but not for
java.lang.String. How come when both are objects?
ThanksPass by value implies that the actual parameter is copied and that copy is used as the formal parameter (that is, the method is operating on a copy of what was passed in)
Pass by reference means that the actual parameter is the formal parameter (that is, the method is operating on the thing which is passed in).
In Java, you never, ever deal with objects - only references to objects. And Java always, always makes a copy of the actual parameter and uses that as the formal parameter, so Java is always, always pass by value using the standard definition of the term. However, since manipulating an object's state via any reference that refers to that object produces the same effect, changes to the object's state via the copied reference are visible to the calling code, which is what leads some folk to think of java as passing objects by reference, even though a) java doesn't pass objects at all and b) java doesn't do pass by reference. It passes object references by value.
I've no idea what you're talking about wrt PreparedStatement, but String is immutable, so you can't change its state at all, so maybe that's what's tripping you up?
Good Luck
Lee
PS: I will venture a guess that this is the 3rd reply. Let's see...
Ok, second. Close enough.
Yeah, good on yer mlk, At least I beat Jos.
Message was edited by:
tsith

Similar Messages

Dear Apple! Sorry for bothering me buy an iphone 5 features of the familiar, I have a pc restore. they forget about icloud account ID and Pass now I want to activate the device without the aid small icloud account and password. lending rules company can

Dear Apple!
Sorry for bothering me buy an iphone 5 features of the familiar, I have a pc restore. they forget about icloud account ID and Pass now I want to activate the device without the aid small icloud account and password. lending rules company can help me to activate the serial number and IMEI states do not ask Thank you!

Apple itself! I'm sorry to bother buying a used iphone 5, I have a pc restore. forget iCloud account ID and now I want to activate the device without iCloud account. Please ask apple can help me to reactivate this device does not need the drill and what? my device is iphone 5 ios 7. If possible please email: [email protected] Thank you very much

Pass by reference and String

public class Test {
    static void method(String str) {
        str = "String Changed";
    public static void main(String[] args) {
        String str = new String("My String");
        System.out.println(str);
        method(str);
        System.out.println(str);
}The output is
My String
My String
How this is possible when objects are passed by reference ?

> How this is possible when objects are passed by reference ?
All parameters to methods are passed "by value." In other words, values of parameter variables in a method are copies of the values the invoker specified as arguments. If you pass a double to a method, its parameter is a copy of whatever value was being passed as an argument, and the method can change its parameter's value without affecting values in the code that invoked the method. For example:
class PassByValue {
    public static void main(String[] args) {
        double one = 1.0;
        System.out.println("before: one = " + one);
        halveIt(one);
        System.out.println("after: one = " + one);
    public static void halveIt(double arg) {
        arg /= 2.0;     // divide arg by two
        System.out.println("halved: arg = " + arg);
}The following output illustrates that the value of arg inside halveIt is divided by two without affecting the value of the variable one in main:before: one = 1.0
halved: arg = 0.5
after: one = 1.0You should note that when the parameter is an object reference, the object reference -- not the object itself -- is what is passed "by value." Thus, you can change which object a parameter refers to inside the method without affecting the reference that was passed. But if you change any fields of the object or invoke methods that change the object's state, the object is changed for every part of the program that holds a reference to it. Here is an example to show the distinction:
class PassRef {
    public static void main(String[] args) {
        Body sirius = new Body("Sirius", null);
        System.out.println("before: " + sirius);
        commonName(sirius);
        System.out.println("after: " + sirius);
    public static void commonName(Body bodyRef) {
        bodyRef.name = "Dog Star";
        bodyRef = null;
}This program produces the following output: before: 0 (Sirius)
after: 0 (Dog Star)Notice that the contents of the object have been modified with a name change, while the variable sirius still refers to the Body object even though the method commonName changed the value of its bodyRef parameter variable to null. This requires some explanation.
The following diagram shows the state of the variables just after main invokes commonName:
main()            |              |
    sirius------->| idNum: 0     |
                  | name --------+------>"Sirius"
commonName()----->| orbits: null |
    bodyRef       |______________|At this point, the two variables sirius (in main) and bodyRef (in commonName) both refer to the same underlying object. When commonName changes the field bodyRef.name, the name is changed in the underlying object that the two variables share. When commonName changes the value of bodyRef to null, only the value of the bodyRef variable is changed; the value of sirius remains unchanged because the parameter bodyRef is a pass-by-value copy of sirius. Inside the method commonName, all you are changing is the value in the parameter variable bodyRef, just as all you changed in halveIt was the value in the parameter variable arg. If changing bodyRef affected the value of sirius in main, the "after" line would say "null". However, the variable bodyRef in commonName and the variable sirius in main both refer to the same underlying object, so the change made inside commonName is visible through the reference sirius.
Some people will say incorrectly that objects are passed "by reference." In programming language design, the term pass by reference properly means that when an argument is passed to a function, the invoked function gets a reference to the original value, not a copy of its value. If the function modifies its parameter, the value in the calling code will be changed because the argument and parameter use the same slot in memory. If the Java programming language actually had pass-by-reference parameters, there would be a way to declare halveIt so that the preceding code would modify the value of one, or so that commonName could change the variable sirius to null. This is not possible. The Java programming language does not pass objects by reference; it passes object references by value. Because two copies of the same reference refer to the same actual object, changes made through one reference variable are visible through the other. There is exactly one parameter passing mode -- pass by value -- and that helps keep things simple.
-- Arnold, K., Gosling J., Holmes D. (2006). The Java� Programming Language Fourth Edition. Boston: Addison-Wesley.
~

Confusion about call-by -value and call - by reference

class A{
public boolean check(String source, ArrayList arr){
//pROCESS ON ARRAYLIST
class B {
A con = new A();
String source="this is string ";
ArrayList arr = new ArrayList();
// suppose Arraylist has some elements
boolean error= false;
error = A.check(source,arr);
}Is it call by value or call by ref .
Please help
}

Object references are also passed by value. ???Yes, as demonstrated byclass Foo {
    public int bar = 0;
    public static void main(String[] args) {
            Foo foo = new Foo();
            foo.bar = 1;
            System.out.println(foo.bar);
            baz(foo);
            // if this was pass by reference the following line would print 3
            // but it doesn't, it prints 2
            System.out.println(foo.bar);
    private static void baz(Foo foo) {
        foo.bar = 2;
        foo = new Foo();
        foo.bar = 3;
}

Confused about licensing with JDev and components

Ok, now I'm very confused.
JDev is free and ADF Faces go to OS but I dont understand what can I deploy and what I cant.
Could some one explain what can I deploy for free and what not,
Regards.

If you are talking specifically about ADF Faces - the version that Oracle provides is part of the overall ADF framework which is free for deployment on the Oracle Application Server and costs money on other servers.
You can pick up the distribution that Apache will provide from the ADF Faces components that we contributed to them - and then you can use those components for Free on any server.
Oracle ADF (the drag and drop data binding and the TopLink or ADF BC components) is again free on Oracle AS, and costs money to deploy on other servers.
And JDeveloper itself is free.

Some confusion about 3D TV's and Syncing Glasses

There has been some confusion about our ad from last week and the offer to sync the 3D glasses with your TV.
We by no means intend to confuse our customers or offer fraudulent services. The offer is new to our stores, and our own employees have been in training just this week. Let me clarify the services included with the Samsung 3D TV offer that appears in this weekend’s insert. Geek Squad will:
Set up and connect your TV + up to 5 components.
Add internet connectable components to your existing wireless network.
Make sure your 3D glasses work.
Review and teach you how to use all of your new gear.
We have some customers who aren’t quite sure how the 3D glasses work, or that the glasses automatically sync with their new 3D TVs. So this informs them that they can depend on Geek Squad to answer their questions during installation and set-up. There is no additional charge for this – and the Geek Squad 3D installation and networking services are included in the total price of this offer.
Matthew
Community Builder
Best Buy Corporate

Can you give details of how you get to £45 per month?
Phone rental and BB Opt 2 ought not to be more that £32
You can opt for line rental saver NOW and that will seriously reduce your bill.
You can also recontract your BB at anytime and unless you recontracted last May or only got BB last May then you are out BB contract and and can cancel or move or negotiate a deal.
If you are really hard up you could cancel Sky as one senior to another.
Life | 1967 Plus Radio | 1000 Classical Hits | Kafka's World
Someone Solved Your Question?
Please let other members know by clicking on ’Mark as Accepted Solution’
Helpful Post?
If a post has been helpful, say thanks by clicking the ratings star.

Confusion about how object interact and are aware of each other

I have this java applet
Two of the classes it contains are the main class with the init method and a UI class that is code for the interface.
the main class instantiates the UI class anonymously (i think you call it that) i.e it does not put it into a named reference it just creates it by calling new without assigning it to anything.
When I click on a button from the UI class I want to call a method in the main class...but how so?
At first I tried to make the function i want to call in the main class static so I could easily call it from the UI class...but then it began to get complex...so i just sent a reference of the main class to the UI class via its constructer.
Now i want the main class to update a JTable in the UI class, but how? It does not have any reference to the UI class.
What is really the standard method of operation for this sort of thing when objects have to be calling methods of each other. How do I make them aware of each other.

the best way to do it is like this:
public class Main {
//this is the main class
private static class MyUIFrame extends JFrame {
    //create the class. It is useable within Main this way
    //static means it doesn't implicitly 'know' about the Main class. You can also
    //remove this and call Main.this to use Main's methods
}Edited by: tjacobs01 on Apr 11, 2009 2:28 AM

Confused about Sony HDR-SR7 and iMovie '08 import

I have my camera set to record at HD XP (15Mb/s). If I look on the camera hard drive at an arbitrary .mts file that is 107.3MB and import that into iMovie '08 at the Full (1920x1080) setting, that 107.3MB file turns into a whopping 854.5MB, while the Large (960x540) setting yields a much more reasonable 287.3MB file size (yet still double the size of the raw file sitting on the hard drive).
There's got to be some re-encoding going on, but what's the point? Why take a 100MB file and explode it to 800MB when you can't get any more quality out of the 100MB file?
Is it just the fact that iMovie doesn't actually support whatever native codec Sony's AVCHD uses, so it needs to re-encode it using AIC whose compression isn't as good as whatever codec AVCHD is using?
So this poses a real dilemma for me - do I import at Full or do I import at Large? Where does one notice the difference? If I blow up the 960 file to display the same size as the 1920 file, I can totally see artifacts on my 30" ACD, but would they show up on my Pioneer plasma TV? PDP-5070HD (1365x768))
Assuming I stay on Full quality - is there any way I can accurately tell how much hard drive space an import is going to consume? Right now my 60GB drive is rammed to the gills and I want to dump it all, but I need to make sure I have the space. 1:8?

Hi
*First: it sounds like you are not importing to iMovie, it sounds like you are trying to browse to the clips. That may not work.*
Ok - I was trying to import and also to view directly on the camcorder (but not at the same time). It was maybe 2 questions rolled into one so apologies if that was confusing...
*Second:You have SD and HD mixed, All of the SD has to be imported before any HD can be imported according to the manual.*
So what would I do, import SD movies first, and then delete it to then import HD specifically? Or do I just import SD and then import HD separately without deleting SD footage from the camcorder?
*Third point: The clips can be on the hard drive or the card. The camera has to be set to the media with the clips you want to import. If you recorded to the card, then switched to the hard drive, you won't be able to import the card video until you switch back.*
I dont have a card at the moment - only using the HDD.
*When you have the import working it is a matter of using the check box to select the clips you want.*
i assume iMovie loads them all up and asks you which ones you want to import?
*Alos one final point for video on the card I find it much easier to use a card reader to import. When I plug in the card reader to my usb port it mounts on the desk top, I start iMovie and the import screen comes up after iMovie is all opened up and running.*
I dont see much point in the card reader at the moment as the HDD is 120GB whereas I assume memory sticks only go to 8GB or so max...
*I hope I have been of some help.*
yes thanks for that - but am still confused by the whoel iMovie & HD import situation and how I should be doing it
All help appreciated

Confused about pixel aspect ratio and video size

Hello,
I have edited a whole dvd full of video and exported it as MPEG-2 NTSC DV Wide - it says 720 x 480, 29.97 fps. I have brought these into Encore and am trying to make a menu but can't seem to get the menu size right. Since I chose the wide format when making the video, which aspect ratio should I use in Encore? It gives me a choice in the properties menu, but when I go to Project settings it says Codec: MPEG-2 Dimensions 720 x 480. Whenever I bring in a menu background from photoshop, it doesn't fit, and is further complicated by the pixel aspect ratio thing. I have no idea what my background size should be to make it fit properly - the templates seem to all be the 4:3 size. What size should I be using in Photoshop and which pixel aspect ratio?
Is my video codec going to cause me a problem in Encore? I assumed that most tvs nowadays are widescreen (at least not square), so I should do the video wide as well.
Thanks for any help! I am thoroughly confused.

Use a template menu from Encore's library. Then modify as you need. That way you know that it will be the right pixel size and par. You cannot made an incorrectly sized/par'd menu work by setting it to 16:9 or 4:3 in the menu properties. It must be correct, and if so, Encore will usually pick the correct setting.
The Encore project settings for DVD really have no choices: it has to be 720x480 for NTSC. There is no project setting for par. You have to create the menu correctly - just let Encore do that for you by using a template.
Was your video source widescreen? If so, then you'll be fine on your video. If not, you may need to sort that out also.

Please help. I need to register a new itouch for my daughter but confused about apple id's and getting all her stuff transferred to the new itouch from the old one. Plus I want her to have her own apple Id

My daughter has an old itouch, she uses my apple I'd. I just got her a new I touch, and want to register it, but give her her own apple Id. I just backed up or synced her old itouch to the computer and now I am setting up her new one. If I give her a new apple Id will she then loose all her apps and songs from her old itouch? Please help!! I thought it was supposed to say something like restore from back up or something like that? Maybe that is a next step after I give her her own apple id?

https://register.apple.com/cgi-bin/WebObjects/GlobaliReg.woa [register an Apple Product]
https://appleid.apple.com/cgi-bin/WebObjects/MyAppleId.woa/wa/createAppleIdForIK B?localang=en_US&path=%2F%2Findex.jspa [create new apple id]
You must be logged in to register an Apple Product
Message was edited by: michael08081

Confused about Cinema 30" MacPro and Radeon x1900 help?

Hey guys, I'm just about to get the 30" monitor for my Macpro which is about 2 years old. I have the ATI radeon x1900xt card installed. I need help
1) Will this card work with the monitor in its fullest resolution?
2) Does the monitor come with that dual link dvi cable, or do I need to spend more money on something else to get the best resolution etc.??
Thanks
Mo

On that video card, both of the DVI outputs are dual-link, meaning it can support two 30" displays at full res, so no problem there.
As far as a dual-link DVI cable is concerned, every 30" monitor that I am familiar with ships with one, so you shouldn't need to buy a separate one. Whatever cable comes with the monitor will give the best resolution.

I'm a bit confused about this 32 bit and 64 bit stuff

Martin Evening's book says "If your computer hardware is 64 bit enabled and you are running a 64 bit operating system, you can run Lightroom as a 64 bit program."
Well I'm currently running XP 64 Bit with 4 GB of RAM inside. How do I run Lightroom in 64 bit mode?
He says Windows 7 users and Windows Vista users will want to buy the 64 bit version of Lightroom. I don't see any 64 bit versions of Lightroom. And for those of us on XP?

Road Worn wrote:
I bought the disc. I explored the disc and I did find the Setup32 and Setup64 on there so I will assume the installer installed the correct version for me.
You can check in task manager, whether LR is running in 32 or 64-bit mode for you. AFAIK, the 32 bit processes should be marked *32 in WinXP also.
What version of LR are you running? Since you installed from CD, you might have LR3.0 installed. In this case I would strongly suggest you download Version 3.4 from here and install it. There have been many bug fixes from 3.0 to 3.4.
Beat

I am confused about the music app and a second playlist

i put music from my computer though ITunes to my IPhone 6 and in the music app I setup one playlist of one artist and then just now I created another playlist and it let me select songs but gives no option to add the music I selec to the second playlist what is going on here

Hey Cooltwou,
To make sure that I am clear and we are on the same page, you cannot add more songs to a playlist that you have already created. You should be able to do that by tapping the edit in the upper left hand corner and then tap the plus button in the upper right hand corner to then select the songs that you have synced to your iPhone.
Playlists
http://help.apple.com/iphone/8/#/iph3cf20cbf
Take it easy,
-Norm G.

Confusion about In-Memory logging and Permanent message

Dear sir:
In the Replication C-GSG.pdf document, it describes as follow:
For the master (again, using the replication framework), things are a little more
complicated than simple message acknowledgment. Usually in a replicated application,
the master commits transactions asynchronously; that is, the commit operation does not
block waiting for log data to be flushed to disk before returning. So when a master is
managing permanent messages, it typically blocks the committing thread immediately
before commit() returns. The thread then waits for acknowledgments from its replicas.
If it receives enough acknowledgments, it continues to operate as normal.
If the master does not receive message acknowledgments — or, more likely, it does not
receive enough acknowledgments — the committing thread flushes its log data to disk
and then continues operations as normal. The master application can do this because
replicas that fail to handle a message, for whatever reason, will eventually catch up to
the master. So by flushing the transaction logs to disk, the master is ensuring that the
data modifications have made it to stable storage in one location (its own hard drive).
My question:
If I have configured IN-Memory Logging in the logging subsystem, is it means that even the master does not receive enough acknowledgments, the committing thread will not flush the log data to disk and just let it stay in the memory region?

Yes, that's correct.
You might find this additional information helpful:
db-4.5.20/docs/ref/program/ram.html

Drag and Drop - Transferable, how to pass a reference? (URGENT)

I've a tree that supports drag and drop correctly but every time I exchange a node position the old parent instance remaining on the tree is different from the one I was referencing with the dragged child before the drag occurred. I absolutely need to maintain all references and cannot work with copies.
Is there any way to use the Transferable interface to pass the original object instead of a copy?
Thanks to Tedhill who raised the problem, trying to get a quick answer.
;o)

hi guys let me close this thread:
Thanks to asjf and sergey35 who helped me.
Actually the isDataFlavorSupported method you suggest passes a reference and not a copy.
Too bad I fell into another problem with the reloading of the
moving-node Object after the DnD.
But finally the working code is:
public class XJTreeDnD extends XJTree implements DragGestureListener, DragSourceListener, DropTargetListener{
private DefaultMutableTreeNode dragNode = null;
private TreePath dragParentPath = null;
private TreePath dragNodePath = null;
private DragSource dragSource;
private DropTarget dropTarget;
private TransferableTreePath transferable;
private boolean DnDEnabled = true;
//private boolean CnPEnabled = false;
public XJTreeDnD(XNode node) {
    super(node);
    // Set up the tree to be a drop target.
    dropTarget = new DropTarget(this, DnDConstants.ACTION_MOVE, this, true);
    // Set up the tree to be a drag source.
    dragSource = DragSource.getDefaultDragSource();
    dragSource.createDefaultDragGestureRecognizer(this, DnDConstants.ACTION_MOVE, this);
private DefaultMutableTreeNode getTreeNode(Point location) {
    TreePath treePath = getPathForLocation(location.x, location.y);
    if (treePath != null) {
      return((DefaultMutableTreeNode) treePath.getLastPathComponent());
    } else {
      return(null);
//dragGesture implementation
    public void dragGestureRecognized(DragGestureEvent e) {
      if(DnDEnabled){
        TreePath path = this.getSelectionPath();
        if (path == null || path.getPathCount() <= 1) {
          System.out.println("Error: Path null, or trying to move the Root.");
          return;
        dragNode = (DefaultMutableTreeNode) path.getLastPathComponent();
        dragNodePath = path;
        dragParentPath = path.getParentPath();
        transferable = new TransferableTreePath(path);
        // Start the drag.
        e.startDrag(DragSource.DefaultMoveDrop, transferable, this);
//dragSource implementation
    public void dragDropEnd(DragSourceDropEvent e) {
      try {
        if (e.getDropSuccess()) {
          ((BaseXJTreeModel)this.getModel()).removeNodeFromParent(dragNode);
          DefaultMutableTreeNode dragParent = (DefaultMutableTreeNode) dragParentPath.getLastPathComponent();
          XNode xnodeParent = (XNode)dragParent.getUserObject();
          ((BaseXJTreeModel)this.getModel()).valueForPathChanged(dragParentPath, xnodeParent);
      } catch (Exception ex) {
        ex.printStackTrace();
    public void dragEnter(DragSourceDragEvent e) {
      // Do Nothing.
    public void dragExit(DragSourceEvent e) {
      // Do Nothing.
    public void dragOver(DragSourceDragEvent e) {
      // Do Nothing.
    public void dropActionChanged(DragSourceDragEvent e) {
      // Do Nothing.
//dropTarget implementation
    public void drop(DropTargetDropEvent e) {
      try {
        Point dropLocation = e.getLocation();
        DropTargetContext dtc = e.getDropTargetContext();
        XJTreeDnD tree = (XJTreeDnD) dtc.getComponent();
        TreePath parentPath = tree.getClosestPathForLocation(dropLocation.x, dropLocation.y);
        DefaultMutableTreeNode parent = (DefaultMutableTreeNode)parentPath.getLastPathComponent();
        Transferable data = e.getTransferable();
        DataFlavor[] flavors = data.getTransferDataFlavors();
        for (int i=0;i<flavors.length;i++) {
          if (data.isDataFlavorSupported(flavors)) {
e.acceptDrop(DnDConstants.ACTION_MOVE);
TreePath movedPath = (TreePath) data.getTransferData(flavors[i]);
DefaultMutableTreeNode treeNodeMoved = (DefaultMutableTreeNode) movedPath.getLastPathComponent();
DefaultMutableTreeNode treeNodeLeft = (DefaultMutableTreeNode) this.dragNodePath.getLastPathComponent();
XNode xnodeParent = (XNode)parent.getUserObject();
XNode xnodeChild = (XNode)treeNodeLeft.getUserObject();
/** @todo check the parent whether to allow the drop or not */
if(xnodeParent.getPath().startsWith(xnodeChild.getPath())){
System.out.println("cannot drop a parent node on one of its children");
return;
if(xnodeParent.getPath().getPath().equals((xnodeChild.getPath().getParentPath()))){
System.out.println("node is already child of selected parent");
return;
// Add the new node to the current node.
xnodeParent.addChild(xnodeChild);
((BaseXJTreeModel)this.getModel()).valueForPathChanged(parentPath, xnodeParent);
((BaseXJTreeModel)this.getModel()).insertNodeInto(treeNodeMoved, parent, parent.getChildCount());
((BaseXJTreeModel)this.getModel()).valueForPathChanged(movedPath, xnodeChild);
e.dropComplete(true);
} else {
System.out.println("drop rejected");
e.rejectDrop();
} catch (IOException ioe) {
ioe.printStackTrace();
} catch (UnsupportedFlavorException ufe) {
ufe.printStackTrace();
public void dragEnter(DropTargetDragEvent e) {
if (isDragOk(e) == false) {
e.rejectDrag();
return;
e.acceptDrag(DnDConstants.ACTION_MOVE);
public void dragExit(DropTargetEvent e) {
// Do Nothing.
public void dragOver(DropTargetDragEvent e) {
Point dragLocation = e.getLocation();
TreePath treePath = getPathForLocation(dragLocation.x, dragLocation.y);
if (isDragOk(e) == false || treePath == null) {
e.rejectDrag();
return;
// Make the node active.
setSelectionPath(treePath);
e.acceptDrag(DnDConstants.ACTION_MOVE);
public void dropActionChanged(DropTargetDragEvent e) {
if (isDragOk(e) == false) {
e.rejectDrag();
return;
e.acceptDrag(DnDConstants.ACTION_MOVE);
private boolean isDragOk(DropTargetDragEvent e) {
/** @todo gestire i casi in cui il drop non sia concesso */
return (true);
public void setDragAndDropEnabled(boolean enabled){
this.DnDEnabled = enabled;
public boolean isDragAndDropEnabled(){
return this.DnDEnabled;
Thanks again.
flat

Confused about passing by reference and passing by valule

Similar Messages

Maybe you are looking for