Passing object reference array to a method
Hi everyone,
I'm new to the java programming language. I want to create create a array of 50 objects and pass them in to a method in other class.
Can anyone help me on this problem........................
Chathu.
Object[] objectArray = new Object[50];
objectArray[0] = "Hello World";
objectArray[1] = new Integer(42);
myClass.myMethod(objectArray);
Similar Messages
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Passing object references to methods
i got the Foo class a few minutes ago from the other forum, despite passing the object reference to the baz method, it prints "2" and not "3" at the end.
but the Passer3 code seems to be different, "p" is passed to test() , and the changes to "pass" in the test method prints "silver 7".
so i'm totally confused about the whole call by reference thing, can anyone explain?
class 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;
class Passer2 {
String str;
int i;
Passer2(String str, int i) {
this.str = str;
this.i = i;
void test(Passer2 pass) {
pass.str = "silver";
pass.i = 7;
class Passer3 {
public static void main(String[] args) {
Passer2 p = new Passer2("gold", 5);
System.out.println(p.str+" "+p.i); //prints gold 5
p.test(p);
System.out.println(p.str+" "+p.i); //prints silver 7
}private static void baz(Foo foo) {
foo.bar = 2;
foo = new Foo();
foo.bar = 3;This sets the bar variable in the object reference by
foo to 2.
It then creates a new Foo and references it by foo
(foo is a copy of the passed reference and cannot be
seen outside the method).
It sets the bar variable of the newly created Foo to
3 and then exits the method.
The method's foo variable now no longer exists and
now there is no longer any reference to the Foo
created in the method.thanks, i think i followed what you said.
so when i pass the object reference to the method, the parameter is a copy of that reference, and it can be pointed to a different object.
is that correct? -
What is the use of passing object reference to itself ?
What is the use of passing object reference to itself ?
regards,
namancThere is an use for returning an object reference from itself, for instance:
class C {
public:
C append(C c) {
// do something interesting here, and then:
return this;
}You can "chain" calls, like this:
C c = new C();
C d = new C();
C e = new C();
c.append (d).append (e);Maybe the OP has "inverted" the common usage, or thought about a static method of a class C that requires a parameter of type C (effectively being a sort of "non-static method").
class C {
static void doAnotherThing (C c) {
c.doSomething(); //-- effectively C.doAnotherThing(c) is an "alternative syntax" for c.doSomething() -
ExternalInterface: pass object reference across interface - how?
I want to invoke methods on specific Javascript or
ActionScript objects through calls across the ExternalInterface
barrier. I would like to be able to do this either AS -> JS or
JS -> AS.
So I would like to pass an object reference across the
interface. I'm not sure exactly what *is* getting passed (is it the
serialized value of the object?), but it doesn't seem to work as an
object reference.
Here's a notional code sample. I have two symmetric object
definitions, one in Javascript, one in ActionScript. During
initialization, one instance of each object will be created and
given a pointer to the other. Then they should each be able to
invoke a method on the other to "do stuff".
//----------[ code ]---------------------------------
//--- Javascript ---
class JSobj {
var _asObj;
JSobj.prototype.setASObj = function(obj) { _asObj = obj; }
JSobj.prototype.callASObj = function(foo) {
callASObjectMethod(_asObj, foo); } // does: _asObj.asMethod(foo);
JSobj.prototype.jsMethod = function(bar) { /* do stuff */ }
function callJSObjectMethod(obj, args) { obj.jsMethod(args);
//--- ActionScript ---
class ASobj {
var _jsObj;
public function set jsObj (obj:Object):void { _jsObj = obj;
public function callJSObj (foo:Number):void {
ExternalInterface.call("callJSObjectMethod", _jsObj, foo); } //
does: _jsObj.jsMethod(foo);
public function asMethod (bar:Number):void { /* do stuff */
function callASObjectMethod (obj:Object, args) {
obj.asMethod(args); }
ExternalInterface.addCallback("callASObjectMethod",
callASObjectMethod);
//----------[ /code ]---------------------------------
My workaround is to pass a uint as an opaque handle for the
object, then resolve it when it is passed back. I'd rather pass a
real reference if possible. Is there a way to pass object
references between JS and AS?
Thanks,
-e-It's an object of a class that extends Object. I guess the answer is no then.
Thanks for your answer -
Passing hard coded array to a method
how to passing hard coded array to a method
like method1("eee","eoe","eee",.....)
which should populate a array of strings (say arr[]) for the method
what can be done??or if you're using Java 5.0 declare the method aspublic void method(String... array) {
} -
Passing a whole array through a method
I need some quick help on how to pass a whole array through the method addCoins(). Here is the code:
public class Purse {
private Coin[] coins;
private int lastIdx;
public Purse() {
coins = new Coin[100];
lastIdx = 0;
public boolean addCoin(Coin b) {
if (lastIdx < coins.length) {
lastIdx++;
coins[lastIdx] = b;
return true;
else {
return false;
public boolean addCoins(Coin[] b) {
if (lastIdx < coins.length) {
for (b=0; b<99; b++) {
coins[b] = b;
else {
return false;
}I figured passing the whole array would be "Coin[] b" but apparently Eclipse says that it can't convert from int to Coin[]. I have no idea what that means. Thanks in advance.I need to create 3 classes, Coin, Purse, and TestPurse.
Coin code:
public class Coin {
private String typeOfCoin;
private double value;
public Coin(String t, double v) {
typeOfCoin = t;
value = v;
public String toString() {
return typeOfCoin + value;
}Purse code:
public class Purse {
private Coin[] coins;
private int lastIdx;
public Purse() {
coins = new Coin[100];
lastIdx = 0;
public boolean addCoin(Coin b) {
if (lastIdx < coins.length) {
lastIdx++;
coins[lastIdx] = b;
return true;
else {
return false;
public boolean addCoins(Coin[] b) {
if (lastIdx < coins.length) {
for (int i=0; i<coins.length; i++) {
coins[i] = b;
else {
return false;
public Coin getReverse() {
coins = new Coin[0];
lastIdx = 100;
}In the Purse class, I need methods addCoin and addCoins that need to return boolean. addCoin is supposed to add the argument coin as an element of the coins array if there is space. addCoins neds to add all the coins in the input argument as elements of the coins array if there is space. I then have to create two methods, getReverse and getValue that take no argument and getReverse that returns an array of type Coin while getValue returns a double. In getReverse, I create an array simlar to coins but this new array is reverse. I started on this method but I first need to worry about the addCoin and addCoins method. For the record, getValue needs to add up the values of all the coins in the purse and return it, which I have no idea how to do that. That's my next question.
Edited by: quagmire87 on Dec 1, 2009 4:35 PM
fixed method addCoins -
Passing object references via methods
Why is the JFrame object not being created in the following code:
public class Main {
public static void main(String[] args) {
Main main = new Main();
JFrame frame = null;
main.createFrame(frame); // <-- does not create the "frame" object
frame.pack();
frame.setVisible(true);
private void createFrame(JFrame frame) {
frame = new JFrame("createFrame");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}Thanks.These explanations are great; real eye openers.
OK. This could be a "way out in left field" question. I am just starting out with Java. But I want to ask:
Objects are stored in the heap?
Object references and primitives are stored on the stack?
Adjusting heap size is straight-forward. A larger heap can store more/larger objects. What about stack sizes?
C:\Dev\java -Xss1024k Main
I assume this refers to method's stacks. But, what about object scoped, and class scoped, object references?
public class Main {
private static List list = new ArrayList(); // class scoped
private JFrame frame = new JFrame(); // object scoped
public static void main(String[] args) { ...... }
private void createFrame() { .... }
}How is the reference to list and frame stored, with regard to memory management?
Do objects have stacks?
Do classes have stacks?
If not, how are the list and frame references stored (which helps me understand reference scoping).
Would the overflow of a method stack (ex. via recurssion) also overflow the method's object and the method's class stacks?
If these questions are stupid, "out of left field", don't matter, etc. Just ignore them.
But the knowledge could help me avoid future memory related mistakes, and maybe pass a "Java Certified Developer" exam?
My original question is already answered, so thanks to all. -
Pass object reference from TestStand to C#
Hi,
I have created a GUI in .NET which i invoke in TestStand (through a custom step type). User can enter a object reference teststand variable in the UI input expression box. So i need to get the object value in that variable and use it to call some .net functions. To get the values from expression box of UI and put in TestStand step variable i use:
PropertyObject.SetValInterface("Step.TestStationObj", 0, tsexprTestStationObj.DisplayText.Trim()); To check the value in the step variable if i do:
MessageBox.Show("TestStation obj after setting:",PropertyObject.GetValInterface("Step.TestStationObj",0).ToString());
But i do not get any value. Guess it is null. Is this a correct way? My intension is to get the value corresponding to a teststand object reference and pass it to C#. The C# UI control is of type NationalInstruments.TestStand.Interop.UI.Ax.AxExpressionEditThanks Andy.
I still get the error when i am trying to pass the object created from C# to Teststand. I have explained what i am trying to do. Kindly requesting your assitance on this issue.
I have 2 classes in C# (code given below), I am trying to pass the object of "Counter" (c1) class from the "Mainfrm" to teststand. In teststand(counter.seq), I am trying to access the function "GetCount() and SetCount()". I have attached the snapshot of the error that i get from teststand.
Class Counter
private int count;
public int GetCount ()
return (count);
public void SetCount(int _count)
count = _count;
Class Mainfrm : Form
public Counter c1;
private void Mainfrm (object sender, EventArgs e)
InitializeComponent();
axApplicationMgr1.Start();
mEngine = axApplicationMgr1.GetEngine();
currentFile = axApplicationMgr1.OpenSequenceFile(@"Counter.seq");
pobj = mEngine.NewPropertyObject(NationalInstruments.TestStand.Interop.API.PropertyValueTypes.PropValType_Container, false, "", 0);
pobj.NewSubProperty("Parameters.ObjRef1", NationalInstruments.TestStand.Interop.API.PropertyValueTypes.PropValType_Reference, false, "", 0);
pobj.SetValInterface("Parameters.ObjRef1", 0, (object)c1);
mExecution = mEngine.NewExecution(currentFile, "MainSequence", null, false, 0, pobj, null, null);
Attachments:
ErrorFromTestStand.JPG 28 KB -
A simple teststand application passing object reference to C#
Hi,
I have a .NET application written in C# which has a UI with NationalInstruments.TestStand.Interop.UI.Ax.AxExpressionEdit controls. This UI is invoked by a custom step in TestStand. One of the values, entered by user in the UI is a object reference variable created in a previous step. I need to store the values entered in the UI during the edit mode of the step, into the TestStand Step variables. And during the run mode i use these values to execute the logic in C#.
The problem is during edit time, the object reference variable, entered in the UI, has no value. It is null. So there is no use storing it at edit time. During the runtime i am trying to retrieve the value of the object reference variable using GetValInterface(...) and GetValIDispatch(..) methods of PropertyObject. But the object returned to C# is of type System.__COMObject wherease in TestStand that object reference is of type .NET.
I don't know how a .NET object reference is converted to COM object when it is returned to .Net function.
Also is there any other method to send this object reference variable's (whose value is '.NET' in previous step itself) value to .NET as a .NET object only so that i can typecast to appropriate type and start using.
Thanks.
Please let me know if anything is not clear.
I have attached the .Net project, .ini file for the custom step and a example sequence file.
Attachments:
CCustomStepObj.zip 23 KBHello Shivapriya,
The example you've sent doesn't compile. And it without it I'm affraid I do not understand the problem you're describing.
You've given references to libraries that you've not attached with your files.
For the C# I see these are the
IADCore.dll
InstrimentInterfaces.dll
TestStand also seems to want to reach for the assembly named TestSystem.dll.
I can only tell you that I have used successfully in the past the Variables in TestStand to hold .NET object references, and call methods on them and I experienced nothing similar that you describe, but I don't quite follow what is the problem here, as I can't use the example.
I would appriciate if you cold narrow down the example to 1 dll or something where the problem occurs and than resend it.
Regards,
Maciej
Message Edited by Mac671 on 09-28-2009 02:59 AM -
Find memory leakage when passing Object Reference from Teststand to vi
I am using Teststand to call labview vi, and pass ThisContext of sequence to vi as object reference, but if I just loop this step and I can find the memory using keep increasing, how can I avoid the memory leakage inside the vi.
see my vi, it is to post message to UI.
Solved!
Go to Solution.You should be using a close reference node to close the references you get as a result of an invoke. In the code below you should be closing the references you get from the following:
AsPropertyObject
Thread
Close those two references once you are done with them.
Also make sure you turned off result collection in your sequence or you will be using up memory continually for the step results.
Hope this helps,
-Doug -
How to pass a file into a java method
I am trying to pass a file into a java method so I can read the file from inside the method. How can I do this? I am confident passing int, char, arrays etc into methods as I know how to identify them in a methods signature but I have no idea how to decalre a file in a mthods signature. Any ideas please ?
ThanksHi,
Just go thru the URL,
http://www6.software.ibm.com/devtools/news1001/art24.htm#toc2
I hope you will get a fair understanding of 'what is pass by reference/value'.
You can pass Object reference as an argument.
What Pablo Lucien had written is right. But the ideal situation is if you are not modifying the
file in the calling method, then you can pass the String (file name) as an argument to the called method.
Sudha -
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?
ThanksHi,
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 -
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.
~ -
Passing object vis-a-vis ThreadLocal, storage...
Hi,
I came across the ThreadLocal object in Java docs.
As per my understanding we could use it store 'common object references' that are required by methods invoked down the line vis-a-vis instead of passing the 'common object references' to all concerned
methods as parameters.
For eg, In a database transaction, the java.sql.Connection object needs to be the same in all crud operations involved so that it can either commited/ rollbacked in one shot.
Am I correct ?
How does storage in a ThreadLocal or passing as parameter compare on the performance aspect.?
g1Thks.
Kayaman u understood my problem but I did not understand u'r statement:
How does storage in a ThreadLocal or passing as
parameter compare on the performance aspect.?
Negligible, if you're concerned about that you shouldn't be writing Java.
To elaborate my scenario....
Say I have a User business object (the db stores the user details and the products he wishes to buy)
So the User BO, will call a singleton - DatabaseSession.startSession(), which obtains a java.sql.connection
to the db and stores it in a local (static) variable of type ThreadLocal.
The BO invokes the UserDAO and ProductDAO in sequence and commits to database (using the same connection, which
can be retrieved from the ThreadLocal var in the singleton).
What I wanted to know was the performance statistics in the scenarios of....
1. keeping the connection instance in a ThreadLocal accessible to all DAO
versus
2. Passing the connection instance to all concerned DAO methods as parameters.
thks
g1 -
Calrification on Pass by reference
Hi All,
In java, if we are passing an object to a function actually we are passing the reference. So, if the function is doing any manipulation on the Object reference, it will affect the passing object.
For example,
class Ob1
int i=0;
public class Ref
public static void main(String a[])
Ob1 o=new Ob1();
System.out.println("Before calling :"+o.i);
call(o);
System.out.println("After calling :"+o.i);
static void call(Ob1 o)
o.i++;
Is it possible to get the original value of i(object Ob1) after calling call()?
Thanks in advance
+Sha> In java, if we are passing an object to a function
actually we are[b] passing the reference.
By value.
Is it possible to get the original value of i(object
Ob1) after calling call()?
Store the original value in a local variable.
And please note the following:
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.
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