Can I define a synchronized method in Interface?

I tried to define a Synchronized method in Interface, but it won't let me compile. So I took the modifier 'Synchronized' out.
When I implement this interface, I was able to implement this method as Synchronized.
Why?
Thanks!

Because synchronisation is an implementation detail and interfaces are not.
Dave

Similar Messages

Defining a customer method in start routine and using in char-routines

Hi,
can I define an own method in start routine and use this method in several routines for characteristics or key-figures?
If yes, can anybody give me a short description where to define the new method (e.g. in wich section of the start routine), where to implement the new method and how to use the new method in transformation of char or key-figures.
Thanks for your help
Thomas

Hi,
If you are looking for something like global method it is not possible. But you can create a function module in SE37 and you can use the same wherever you want.
Regards
Githen

Pbroblems with Synchronized methods --- please help

** One Thread calls a synchronized method using an object (obj1) of a Class (Class name - meth_class) and occupies the monitor of that particular object (obj1). Then no other Thread can call that particular synchronized method or any other synchronized method of the object (obj1) of a Class (Class name - meth_class). **
          IF THE ABOVE DEFINITION IS TRUE PLEASE HELP ME OUT WITH THE FOLLOWING:
Please go through the code below:-
class meth_class
          volatile boolean valueset=false;
          int var;
          synchronized int get()
                    if (!valueset)
                              try
                                        wait();
                              catch (InterruptedException e)
                                        System.out.println("Consumer interrupted");
                    System.out.println("Get - " + var);
                    valueset=false;
                    notify();
                    return var;
          synchronized void put(int x)
                    if (valueset)
                              try
                                        wait();
                              catch (InterruptedException e)
                                        System.out.println("Producer interrupted");
                    this.var=x;
                    System.out.println("Put - " + var);
                    valueset=true;
                    notify();
class producer implements Runnable
          meth_class obj;
          Thread thrd;
          producer(meth_class x)
                    obj=x;
                    thrd=new Thread(this, "Producer");
                    thrd.start();
          public void run()
                    int var=0;
                    while(true)
                              obj.put(var++);
class consumer implements Runnable
          meth_class obj;
          Thread thrd;
          consumer(meth_class x)
                    obj=x;
                    thrd=new Thread(this, "Consumer");
                    thrd.start();
          public void run()
                    while(true)
                              obj.get();
class main_thrd
          public static void main(String args[])
                    meth_class obj=new meth_class();
                    new producer(obj);
                    new consumer(obj);
                    System.out.println("Press Control-C to stop");
My Questions are:
1.     class main_thrd creates two objects as ?new producer(obj)? and ?new consumer(obj)?. Now both these objects creates 2 threads and try to call two different Synchronized methods of same CLASS ? ?meth_class? through a single object by the name of ?obj? created in class main_thrd. Now as ?new producer(obj)? object is created first in the class main_thrd, the Thread created by it enters the monitor of object (obj) and locks it. Then as per the rule the Thread created by ?new consumer(obj)? object never gets to occupy the monitor of the object (obj) because Producer is in an infinite loop. BUT THEN WHY WE HAVE ? GET - ** ? VALUES PRINTED IN THE OUTPUT.
Please any one help me out,
(THANKS FOR ALL YOUR HELP)

Now as ?new producer(obj)? object is called first in the class main_thrd, the Thread created by it enters the monitor of object (obj) and locks it.Though new producer(obj) is called first, it is not necessary that the thread created by it gets the lock of object(obj) first. This is false
assumption.
Next, even if we assumed that it gets the lock of given object first,
while(true)
    obj.put(var++);
}The lock of Object(obj) is released when the obj.put(var++) returns and any one can get hold of lock of the Object(obj) at that instant.
In fact, next time obj.put(var++) is called, it will have to wait until it can get lock of the given object.

Synchronized method in a java class used by many interfaces

My interface (idoc to file) is using a java class, which has one method that reads a table from a central database and after doing some calculations updates it.
(The interface instantiate the class inside a user-defined function and calls the method there.)
The problem is that if somebody sends 100 idocs at the same time, there can be a dirty read, I mean, a read just before other interface updates the table.
We want the following:
Interface 1:
- Read counter from the table (counter = 5 )
- Increment counter (counter = 6)
- Update table with that counter (table with counter = 6)
Interface 2:
- Read counter from the table (counter = 6 )
- Increment counter (counter = 7)
- Update table with that counter (table with counter = 7)
RESULT: The table has the counter = 7
But what is happening is the following:
- Interface 1 reads (counter = 5)
- Interface 2 reads (counter = 5)
- Interface 1 increments counter (counter = 6)
- Interface 2 increments counter (counter = 6)
- Interface 1 updates table (table with counter = 6)
- Interface 2 updates table (table with counter = 6)
RESULT: The table has the counter = 6 (WRONG)
I made the method synchronized. What I was expecting was that only one interface (i1) could enter the method (read the table and update it) while other interfaces running at the same time would have to wait until i1 finished that method.
My first test indicates that's not happening. Can anybody help me to find a solution?

Hi Bhavesh,
If the QOS is EOIO this means that the integration engine manage the call to the mapping program (and all the other blocks) inside an "internal" synchronized method.
So this means that in this case you do not need to manage the queued access (synchronization) inside your custom java code because it is already enveloped in a queued block by XI.
The problem that Jorge had can be easily reproduced using the sample code that follows:
class Synch Object
import java.util.Date;
public class SynchObject {
 String strName;
 public SynchObject(String strName){
 this.strName = strName;
 public synchronized void syncWrite(String strCaller) throws InterruptedException{
 Date now;
 now = new Date();
 System.out.println("-- " + now.toLocaleString() + " " + strCaller + " entering syncWrite of " + strName);
 System.out.flush();
 Thread.sleep(1000);
 now = new Date();
 System.out.println("-- " + now.toLocaleString() + " syncWrite of " + strName + " called by " + strCaller );
 System.out.flush();
 Thread.sleep(1000);
 now = new Date();
 System.out.println("-- " + now.toLocaleString() + " " + strCaller + " leaving syncWrite of " + strName);
 System.out.println("");
 System.out.flush();
class Caller
public class Caller implements Runnable {
 String strName;
 SynchObject target;
 int intMax;
 public Caller(String strName, SynchObject target, int intMax) {
 this.strName = strName;
 this.target = target;
 this.intMax = intMax;
 public void run() {
 for(int i=0; i<intMax;i++)
 try {
 target.syncWrite(strName);
 } catch (InterruptedException e) {
 e.printStackTrace();
class Workbench
public class Workbench {
 public static void main(String[] args) {
 // TODO Auto-generated method stub
 SynchObject sObj1 = new SynchObject("syncObj1");
 SynchObject sObj2 = new SynchObject("syncObj2");
 Caller c1 = new Caller("caller1",sObj1,2);
 Caller c2 = new Caller("caller2",sObj1,2); '[*CHANGE*]
 Thread ct1 = new Thread(c1);
 Thread ct2 = new Thread(c2);
 ct1.start();
 ct2.start();
Run the workbench class to see what happen when setting QOS EOIO (the synch object is the same).
To see instead what happen now (missing synchronization) you have to change in Workbench class the statement
Caller c2 = new Caller("caller2",sObj1,2); '[*CHANGE*]
with
Caller c2 = new Caller("caller2",sObj2,2); '[*CHANGE*]
The reason is that every instance of the mapping program declare a new instance of the "Synchronized object" so the calls are synchronized inside the same mapping program but not between several mapping program.
Hope this give you a better idea on this problems with java synchronization, but if you have further doubts (I know it's a little bit tricky ) feel free to ask.
Kind Regards,
Sergio

How to create a method in Interface Controller

Hi Guys,
        I am working with webdynpro ABAP sample application "Component usage" . There i got a issue like i am not able to create a method in Interface controller. There i am not able to edit anything. Can anybody please let me know how to do that.
            Thanks In Advance
Regards
Ravikumar

Hi Ravi,
          Check This
If one Web Dynpro component (parent component) needs access to another Web
Dynpro component (child component) the parent component can declare the use
of the child component. A specific component usage instance is then created and
the parent component accesses the functionality of the child component via its
component interface controller.
The only parts of a Web Dynpro component that are visible to the user, are the
interface controller and the interface view(s).
All Web Dynpro components have only one interface controller. Via the
interface controller, data, methods, and event handlers can be exposed to
other components.
Interface views represent the visual interface of a Web Dynpro component.
There is a one-to-one relationship between a Window and an interface view.
Each time a window is defined, a related interface view is automatically
generated, which makes the window accessible from outside the component.
The interface view only exposes those inbound and outbound plugs to the
component user that have the interface property checked. Methods and
context data of the window are not accessible via the related interface view.
If the component has no views, there is no need to have Windows. In this
case, the component will not implement an interface view. Such components
having no visual interface are known as faceless components.
Regards
Sarath

Protected Methods in Interfaces

Why don't interfaces allow you to declare protected methods? Is there a way around this?
The reason I ask involves a current project of mine. I have an inheritance hierarchy including an abstract Event base class with many concrete derived Events. I want to define many protected methods in the base Event class, which all my derived Events will use, in order to save me a lot of coding. I'm also trying to make my program reusable, and isolate the protocol changes to this Event hierarchy and a Packet hierarchy as well. For both these hierarchies, I want to implement interfaces that make sure that the programmer defines these necessary, protected methods. Yet I cannot declare protected methods in my interfaces!

> I have this same desire: to have protected
methods within interfaces.
Interfaces are not intended to (nor can they) provide
implementation.Yes, this is clear. Yet they "promise" an implementation. In the Java interface model, they only promise the public interface. I have yet to see why they cannot promise protected methods. I'm not really interested in code inheritance (reusing the code). I'm interested in what is called interface inheritance to achieve certain polymorphic goals.
>
> any design patterns that can be used to get
around this problem.
I'd suggest using composition rather than
inheritance. Let me know if I should explain
further.
Yes, I understand about composition (or delegation) as a way to "inherit" the functionality; however, I want to treat the subclasses polymorphically. I'm designing class library/frameworks that require a certain level of structure. The subclasses need to maintain the encapsulation provided by protected methods. I don't want external clients calling the protected methods, but the only way to achieve multiple (interface) inheritance is through Java's public interfaces, which then exposes the methods. I see no way around this problem. I'm not familar with the technical challenges of implementing multiple inheritance within compilers etc. At first glance, I don't see why allowing methods to be declared protected within the Java interface construct would cause serious technical problems.
~
P.S. Yes, this is an old thread...
Sorry, yes this is an old thread. I did some searching on this topic and this thread came up. Thanks for your reply.

Can I no longer browse classes in interface builder?

in tiger, I used to be able to browse classes in interface builder, and from their I could create subclasses, and create actions and outlets. then I could create files for the classes from the classes menu. then when I went back to xcode I would have empty class file templates that I could then write the methods for.
also, I could easily instantiate my class via the classes menu.
alas, now I cannot find these features. have they dissappeared entirely? is there an equivilant way to do this?

I found that disturbing too...
However the system changed completely. You can no longer define the super-class directly in Interface Build, however you can still define classes there with IBOutlets and IBActions.
First, to instantiate a blue cube as a custom object, simply drag a blue cube from the Library windows inside : Library --> Cocoa --> Objects & Controllers --> Controllers.
To set the class, go in Identity inspector (CMD + 6) here you'll be able to define the class name, its outlets and its actions, you can even define the action argument type (sender) here, however, weirdly, they took the ability to add the colon directly at the of the method name, so you'll have to add it yourself.
However, Apple documentation advise you to add methods and outlets directly in Xcode and not in IB, "Whenever you want to create a new controller class, or add an outlet or action to an existing class, do it in Xcode."
Indeed, if IB is opened at the same time, it will update the class's outlets and actions directly, Xcode and IB are more binded together than before.
Message was edited by: PsychoH13

Differences between Synchronized methods and blocks

Hi all,
I would like to differences between Synchronized methods and blocks.
- Muni

Well, you'll get so many of right answers in next ten to thirty minutes.
I like to yield :)
Oooo... Ten minutes has passed.
Synchronized block is a toilet room with a lock in a public lavatory.
Only one person(running thread) can have the lock at a time.
And, she/he have to receive the lock from a particular object obj like:
synchronized(obj){.....} // one object has only one lock for this {} toilet and for any other toilets how many there are... *
(*: In other words, while a thread is executing a synchronized(obj){} block, other threads can't enter other synchronized(obj){} blocks.)
Synchronized method is a kind of synchronized block.
This special block is defaulted to have lock from the object on which the method is defined.
public class Foo{public synchronized Method(){}}
use the lock of a Foo object.
Message was edited by:
hiwa
Message was edited by:
hiwa

Which object's monitor does a synchronized method acquire?

from the Java Tutorial for concurrency programming:
" When a thread invokes a synchronized method, it automatically acquires the intrinsic lock _for that method's object_ and releases it when the method returns. The lock release occurs even if the return was caused by an uncaught exception. "
what exactly does this mean?
do synchronized methods acquire the monitors for objects of type: java.lang.reflection.Method
please consider this code:
public class Foo {
private int counter = 0;
public synchronized void incriment() { counter++; }
public synchronized void decriment() { counter--; }
Foo f = new Foo();
Class[] sig = new Class[0];
Method m = f.getClass().getMethod("incriment", sig);
// ok. so "m" is the relevant method object.
f.incriment(); // <-- is the monitor for "m" ,
// or the monitor for "f", acquired?
.......my reading of the Concurrency Tutorial is that synchronized methods use the monitors of java.lang.reflection.Method objects?
and thus, Foo is not thread safe, right?
however, this simple change makes Foo thread-safe?
public class Foo {
private volatile int counter = 0; // "volatile"
public void incriment() { counter++; }
public void decriment() { counter--; }
}thanks.
Edited by: kogose on Feb 23, 2009 7:13 PM

tensorfield wrote:
jverd wrote:
tensorfield wrote:
kogose wrote:
what exactly does this mean?It means you're complicating things.
If a method is synchronized, it is. You don't need to go beyond that. The method is synchronized.Not true. You have to know what it means for a method to be synchronized. Often people come in with the erroneous impression that it somehow prevents you from using or accessing the object in any other thread.It's very simple. If a synchronized method is called at the same time from many threads only one call will be executed at a time. The calls will be lined up and performed one after the other in sequence.
AND because synchronization is on a per object basis, when one synchronized method is being called from one thread, all synchronized methods of that same object are blocked for calling from other threads.
Simple as that.No, it's not that simple, and as stated, that is not correct. In particular, you didn't mention that for an instance method, all the various threads have to be trying to call instance methods on the same object in order for execution to be sequential.
You really can't understand Java's syncing without understanding how it relates to locks, and what it means for a method to be synchronized in terms of which lock it acquires.
Edited by: jverd on Feb 25, 2009 2:47 PM

How do i get a list of all Roles defubed under a particular OrganizationalUnit? How can i use LDAPConnection.search method for this?

Sorry for the typographical mistake.
Please read the question as:"How do i get a list of all Roles defined under a particular OrganizationalUnit? How can i use LDAPConnection.search method for this?"

Hello can anybody help me to build an interface

hello can you help me to build an interface that can work with this english to private talk converter code
import java.util.Map;
import java.util.HashMap;
import java.util.Iterator;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.BufferedReader;
import java.io.FileReader;
public class Translate
public static void main(String [] args) throws IOException
if (args.length != 2)
System.err.println("usage: Translate wordmapfile textfile");
System.exit(1);
try
HashMap words = ReadHashMapFromFile(args[0]);
System.out.println(ProcessFile(words, args[1]));
catch (Exception e)
e.printStackTrace();
// static helper methods
* Reads a file into a HashMap. The file should contain lines of the format
* "key\tvalue\n"
* @returns a hashmap of the given file
@SuppressWarnings("unchecked")
private static HashMap ReadHashMapFromFile(String filename) throws FileNotFoundException, IOException
BufferedReader in = null;
HashMap map = null;
try
in = new BufferedReader(new FileReader(filename));
String line;
map = new HashMap();
while ((line = in.readLine()) != null)
String[] fields = line.split("\\t", 2);
if (fields.length != 2) continue; //just ignore "invalid" lines
map.put(fields[0], fields[1]);
finally
if(in!=null) in.close(); //may throw IOException
return(map); //returning a reference to local variable is safe in java (unlike C/C++)
* Process the given file
* @returns String contains the whole file.
private static String ProcessFile(Map words, String filename) throws FileNotFoundException, IOException
BufferedReader in = null;
StringBuffer out = null;
try
in = new BufferedReader(new FileReader(filename));
out = new StringBuffer();
String line = null;
while( (line=in.readLine()) != null )
out.append(SearchAndReplaceWordsInText(words, line)+"\n");
finally
if(in!=null) in.close(); //may throw IOException
return out.toString();
* Replaces all occurrences in text of each key in words with it's value.
* @returns String
private static String SearchAndReplaceWordsInText(Map words, String text)
Iterator it = words.keySet().iterator();
while( it.hasNext() )
String key = (String)it.next();
text = text.replaceAll("\\b"+key+"\\b", (String)words.get(key));
return text;
* @returns: s with the first letter capitalized
String capitalize(String s)
return s.substring(0,0).toUpperCase() + s.substring(1);
... here's the head of my pirate_words_map.txt
hello     ahoy
hi     yo-ho-ho
pardon me     avast
excuse me     arrr
yes     aye
my     me
friend     me bucko
sir     matey
madam     proud beauty
miss     comely wench
stranger     scurvy dog
officer     foul blaggart
where     whar
is     be
are     be
am     be
the     th'
you     ye
your     yer
tell     be tellin'

hakimade wrote:
hello can you help me to build an interface that can work with this english to private talk converter codeYou might want to re-ask this question in such a way that it can be answered.
Also, when posting your code, please use code tags so that your code will retain its formatting and be readable. To do this, either use the "code" button at the top of the forum Message editor or place the tag [code] at the top of your block of code and the tag [/code] at the bottom, like so:
[code]
// your code block goes here.
// note the differences between the tag at the top vs the bottom.
[/code]or
{code}
// your code block goes here.
// note here that the tags are the same.
{code}Good luck.

Calling static synchronized method in the constructor

Is it ok to do so ?
(calling a static synchronized method from the constructor of the same class)
Please advise vis-a-vis pros and cons.
regards,
s.giri

I would take a different take here. Sure you can do it but there are some ramifications from a best practices perspective. f you think of a class as a proper object, then making a method static or not is simple. the static variables and methods belong to the class while the non-static variables and methods belong to the instance.
a method should be bound to the class (made static) if the method operates on the class's static variables (modifies the class's state). an instance object should not directly modify the state of the class.
a method should be bound to the instance (made non-static) if it operates on the instance's (non-static) variables.
you should not modify the state of the class object (the static variables) within the instance (non-static) method - rather, relegate that to the class's methods.
although it is permitted, i do not access the static methods through an instance object. i only access static methods through the class object for clarity.
and since the instance variables are not part of the class object itself, the language cannot and does not allow access to non-static variables and methods through the class object's methods.

Use of 'static' keyword in synchronized methods. Does it ease concurrency?

Friends,
I have a query regarding the use of 'synchronized' keyword in a programme. This is mainly to check if there's any difference in the use of 'static' keyword for synchronized methods. By default we cannot call two synchronized methods from a programme at the same time. For example, in 'Program1', I am calling two methods, 'display()' and 'update()' both of them are synchronized and the flow is first, 'display()' is called and only when display method exits, it calls the 'update()' method.
But, things seem different, when I added 'static' keyword for 'update()' method as can be seen from 'Program2'. Here, instead of waiting for 'display()' method to finish, 'update()' method is called during the execution of 'display()' method. You can check the output to see the difference.
Does it mean, 'static' keyword has anything to do with synchronizaton?
Appreciate your valuable comments.
1. Program1
public class SynchTest {
     public synchronized void display() {
          try {
               System.out.println("start display:");
               Thread.sleep(7000);
               System.out.println("end display:");
          } catch (InterruptedException e) {
               e.printStackTrace();
     public synchronized void update() {
          try {
               System.out.println("start update:");
               Thread.sleep(2000);
               System.out.println("end update:");
          } catch (InterruptedException e) {
               e.printStackTrace();
     public static void main(String[] args) {
          System.out.println("Synchronized methods test:");
          final SynchTest synchtest = new SynchTest();
          new Thread(new Runnable() {
               public void run() {
                    synchtest.display();
          }).start();
          new Thread(new Runnable() {
               public void run() {
                    synchtest.update();
          }).start();
Output:
Synchronized methods test:
start display:
end display:
start update:
end update:
2. Program2
package camel.java.thread;
public class SynchTest {
     public synchronized void display() {
          try {
               System.out.println("start display:");
               Thread.sleep(7000);
               System.out.println("end display:");
          } catch (InterruptedException e) {
               e.printStackTrace();
     public static synchronized void update() {
          try {
               System.out.println("start update:");
               Thread.sleep(2000);
               System.out.println("end update:");
          } catch (InterruptedException e) {
               e.printStackTrace();
     public static void main(String[] args) {
          System.out.println("Synchronized methods test:");
          final SynchTest synchtest = new SynchTest();
          new Thread(new Runnable() {
               public void run() {
                    synchtest.display();
          }).start();
          new Thread(new Runnable() {
               public void run() {
                    synchtest.update();
          }).start();
Output:
Synchronized methods test:
start display:
start update:end update:
end display:

the synchronized method obtain the lock from the current instance while static synchronized method obtain the lock from the class
Below is some code for u to have better understanding
package facado.collab;
public class TestSync {
     public synchronized void add() {
          System.out.println("TestSync.add()");
          try {
               Thread.sleep(2000);
          } catch (InterruptedException e) {
               e.printStackTrace();
          System.out.println("TestSync.add() - end");
     public synchronized void update() {
          System.out.println("TestSync.update()");
          try {
               Thread.sleep(2000);
          } catch (InterruptedException e) {
               e.printStackTrace();
          System.out.println("TestSync.update() - end");
     public static synchronized void staticAdd() {
          System.out.println("TestSync.staticAdd()");
          try {
               Thread.sleep(2000);
          } catch (InterruptedException e) {
               e.printStackTrace();
          System.out.println("TestSync.staticAdd() - end");
     public static synchronized void staticUpdate() {
          System.out.println("TestSync.staticUpdate()");
          try {
               Thread.sleep(2000);
          } catch (InterruptedException e) {
               e.printStackTrace();
          System.out.println("TestSync.staticUpdate() - end");
     public static void main(String[] args) {
          final TestSync sync1 = new TestSync();
          final TestSync sync2 = new TestSync();
          new Thread(new Runnable(){
               public void run() {
                    sync1.add();
          }).start();
          new Thread(new Runnable(){
               public void run() {
                    sync2.update();
          }).start();
          try {
               Thread.sleep(3000);
          } catch (InterruptedException e) {
               e.printStackTrace();
          new Thread(new Runnable(){
               public void run() {
                    sync1.staticAdd();
          }).start();
          new Thread(new Runnable(){
               public void run() {
                    sync2.staticUpdate();
          }).start();
}

Need of more than one synchronized methods

Inside my run method I'm calling a synchronized method which in turn calls other synchronized methods of the same and another class.
Now if the top level method is synchronized, does the need to make other methods synchronized still remain ?
Won't the other threads wait till the thread using the top level synchronized method returns.
Vik

Well, if you can be sure that the second method is not going to be called some other way except within that first synchronized method, then no it's not needed.

Static methods in interface (Yes, once again!)

I know there has been many questions about why static methods in interfaces are not allowed. I know it is forbidden by the JLS. But does anyone know the exact reason for this? Is it just a design issue or are there technical difficulties with allowing it?
I can't think of any reason that it should be impossible to allow static methods in interfaces. I don't even think it would be very difficult to do. More importantly, it could probably be done without breaking existing code and existing JVMs (not too sure about the last one).
So once again: Was the choice of not allowing static methods in interfaces a design choice or a technical choice?

A better example of what you are suggesting is surely ...
interface i {
    static void one();
class a implements i {
    static void one() {
        // do something
class b implements i {
    static void one() {
        // do something else
}What would be the point of ever doing this?
You cant call i.one() as the method doesn't exist without an instance of an implementing class.
To actually ever be able to use that method you would effectively be casting an INSTANCE of a or b -> i. If you have an instance of an a or b then there is absolutely no reason for that method to be static.
If you wanted to implement some sort of class (ie static) behaviour then class a could call its own internal static method from within the 'one' method.
To get right to the point ... there isn't one. If it gets added to the language (and I can't see it in my wildest dreams) then Sun have lost their marbles, surely?
Unless someone can give a good example of when it might be correct and useful to do so? I can't even see how it would be a convenience as it is completely unusable, no?

Can I define a synchronized method in Interface?

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