Native method in object class........

I would like to know that which method of object class is a native method..........

flounder wrote:
The natives are getting restless.
What they do with him when he arrives, I don't know.This reminds me of one of my favorite entries in Ambrose Bierce's [Devil's Dictionary|http://en.wikipedia.org/wiki/Devil%27s_dictionary]
h3. Aborigines
Persons of little worth found cumbering the soil of a newly discovered country. They soon cease to cumber; they fertilize.

Similar Messages

Interfaces and methods of Object class

JSL 2.0 states the following
If an interface has no direct superinterfaces, then the interface implicitly
declares a public abstract member method m with signature s, return type r,
and throws clause t corresponding to each public instance method m with
signature s, return type r, and throws clause t declared in Object, unless a
method with the same signature, same return type, and a compatible throws
clause is explicitly declared by the interface.
But the following codes produces empty output
package test;
import java.lang.reflect.Method;
public class TestIterface {
    public static void main(String [] args){
        Method [] methods=Y.class.getMethods();
        for(int i=0, n=methods.length;i<n;i++)
            System.out.println(methods);
interface Y{
What are the reasons of such behaviour?

then the interface implicitly declares a public abstract member method
"Implicit" means that it's implied that the interface declares those methods; unlike java.lang.Object, there is no interface from which all other interfaces descend. All interfaces at the "top" of the inheritance hierarchy are implied to expose at least the same methods as Object.
Hope this helps...

How do interfaces have methods of Object class

Hi All,
Please consider the following code snippet.
public interface EmployeeService
    public void createEmployee(Employee emp);
    public Employee findEmployee(String empId);
public class EmployeeServiceImpl implements EmployeeService
    public void createEmployee(Employee emp) { ................. }
    public Employee findEmployee(String empId) { ................. }
}The above is a simple example where I have an employee object with two service methods to create and find an employee.
Now the consider the following
EmployeeService empService = new EmployeeServiceImpl();
Employee emp = empService.findEmployee("1").So the above code helps me in finding an employee.
Now, we know that you can only call those methods that are defined in the interface.
My question is, if I use the empService you would be able to access the methods of the Object class (equals, hashCode, wait etc.)
How does this happen? In the Jave API we know all class by default override the Object class, so how does it work with interfaces?
Thanks in advance for the reply

[JLS 6.4.4 The Members of an Interface Type|http://java.sun.com/docs/books/jls/third_edition/html/names.html#6.4.4] says:
If an interface has no direct superinterfaces, then the interface implicitly declares a public abstract member method m with signature s, return type r, and throws clause t corresponding to each public instance method m with signature s, return type r, and throws clause t declared in Object, unless a method with the same signature, same return type, and a compatible throws clause is explicitly declared by the interface. It is a compile-time error if the interface explicitly declares such a method m in the case where m is declared to be final in Object.
So, in short, those methods exist in interfaces because the JLS says they do.

Native method in local class

Hi there,
this is a repost of my question but now in the right forum.
I have a problem with a native method of a local class that hides a member class:
public class SomeClass
     class MemberClass
          public native void bla();
          public void out()
               System.out.println("A");
     public void foo()
          class MemberClass
               public native void bla();
               public void out()
                    System.out.println("B");
          MemberClass myClass = new MemberClass();
          myClass.out();
     public static void main(String[] args)
          SomeClass someClass = new SomeClass();
          someClass.foo();
}The class MemberClass exist in two different ways. Every class has it's own out() method. The local class just hides the member class. Now I want to implement the native methods bla() of the two classes.
If I call
javac SomeClass.hI get
SomeClass.class
SomeClass$MemberClass.class
SomeClass$1MemberClass.classwhich makes sense to me. We have one class file for the member class and one for the local class.
If I use
javah SomeClassthen I get
JNIEXPORT void JNICALL Java_SomeClass_00024MemberClass_bla(JNIEnv *, jobject);in the header file for the member class. No header file for the local class was created.
Therefore I call
javah SomeClass$1MemberClassand I get another header file which is for the local class. But this header file declares the same native method:
JNIEXPORT void JNICALL Java_SomeClass_00024MemberClass_bla(JNIEnv *, jobject);This is ambiguous... If I would implement the native method, then I couldn't even say for which one of the native methods it will be used. Maybe for both.. which wouldn't make any sense too.
What is wrong here?
Thank you for your thoughts :-)

Interesting...From the JLS under "fully qualified name"
[http://java.sun.com/docs/books/jls/third_edition/html/names.html#71701]
"Every package, top level class, top level interface, and primitive type has a fully qualified name."
From the javah docs
javah [ options ] fully-qualified-classname
And note this under the JNI spec for "FindClass"
[http://java.sun.com/javase/6/docs/technotes/guides/jni/spec/functions.html#wp16027]
"The name argument is a fully-qualified class name or an array type signature "
Does that mean that you can't use JNI to access a local class? Seems like I have seen posts that said that was possible.

Native methods inside C++ class

Hey all,
Tried posting this already but it didn't appear in the forums. So apologies if this appears twice on same forum :o)
Want to wrap my native methods inside a C++ class but get UnsatisfiedLinkerError when I do. Is it possible to do this? Do I have to change some method signatures or what?
I want something like :
public class A
native void doSomething();
class B
public:
JNIEXPORT void JNI Java_A_doSomething() { ... } /* or whatever */
It works ok outside of a C++ class but I'd prefer to contain my methods inside a class. Any help?
Cheers,
Conor

Java needs to find your functions in the DLL or SO. But the names are "mangled" if you declare the function inside a class - even declaring the function "static" does not help. For instance, using the Microsoft C++ compiler:
class B
public:
static JNIEXPORT void JNI Java_A_doSomething() { ... }
};the name is mangled to ?Java_A_doSomething@B@@SAXXZ
But Java tries to locate the entry _Java_A_doSomething@0 in the DLL.
You can write the global functions as:
JNIEXPORT void JNI Java_A_doSomething() {
B::doSomething();
}and implement your functions in the class B. The advantage of this approach is that you can write all bookkeeping work of converting Java data to C++ data in the global function, and leave the real work to the function declared in the C++ class.

Is Method.invoke (Object,Class[]) efficient

hi
How efficient is the method invoke compared to explicit method calling?
thanks

I cna't give any solid numbers either, but when I've used it I've noticed it to be much slower than directly invoking the method. Ballpark I'd guess 5 times as much overhead, but don't hold me to that. Of course, if the work your method does is large compared to method invocation overhead, then it shouldn't really matter.

Calling native methods in a package

Hi!
We have a problem when calling native methods in a class which is in a package. As you can see from the code below we have a class making an instance of a class<testBando> which makes a instance of another class<Bando> which contains the native methods. When running the program we get the error:
Exception in thread "main" java.lang.UnsatisfiedLinkError: initialize
at test2.Bando.initialize(Native Method)
at test.testBando.<init>(testBando.java:10)
at Main.main(Main.java:5)
When we take the class that calls the native methods out of any package every thing works fine! Can you not call native methods inside a package or what are we doing wrong?
// testBando.java
package test;
import test2.*;
public class testBando {
Bando b;
public testBando() {
     b = new Bando();
     b.initialize();
// Bando.java
package test2;
public class Bando {
public native void initialize();
static {
     System.loadLibrary("bando");
// Main.java
import test.*;
public class Main {
public static void main(String[] args) {
     new testBando();

I suspect that your problem is that you have not
regenerated the signature when you placed the native
method's object in a package. Or same result but different sourc:
-package name was changed and it wasn't regen'd
-javah was run incorrectly (which gens the signatures with no package name.)

Calling native method

Guys please help me with following error.
I am running a simple JNI program,after creating and loading the dll i am getting following error.......
Exception in thread "main" java.lang.UnsatisfiedLinkError: print
"print" is the native method in java class Hello.java
Hello.h has method declaration as :
JNIEXPORT void JNICALL Java_Hello_print
(JNIEnv *, jobject);
and C++ file has method defined as :
JNIEXPORT void JNICALL
Java_Hello_print(JNIEnv *env, jobject obj)
printf("Hello World!\n");
return;
please help me out...it has been 3 days banging against JNI ...

Guys please help me with following error.
I am running a simple JNI program,after creating and
loading the dll i am getting following error.......
Exception in thread "main"
java.lang.UnsatisfiedLinkError: print
"print" is the native method in java class
Hello.java
Hello.h has method declaration as :
JNIEXPORT void JNICALL Java_Hello_print
(JNIEnv *, jobject);
and C++ file has method defined as :
JNIEXPORT void JNICALL
Java_Hello_print(JNIEnv *env, jobject obj)
printf("Hello World!\n");
return;
please help me out...it has been 3 days banging
against JNI ...If your Java code is in a package, then your native header file declaration is wrong. The javah tool expects the fully qualified class name. So, if your Hello class is in package com.foo.hello, you should generate the header file like this:
javah com.foo.hello.HelloThen the native header declaration will look like this:
JNIEXPORT void JNICALL Java_com_foo_hello_Hello_print
(JNIEnv *, jobject);

HashCode function in Object class.

Hi! to all!
I have got a confusion about hashCode function of Object class, which returns an integer.
What is the real purpose of introducing this method in Object class.
Please comment.

hashCode() method of the object is intorduced for the benefit of collections like HashTables. Typically
hashCode method should return distinct integers for distinct objects which are decided distinct based on
equals method of the object. Though this is not mandatory , if distinct objects have distinct
hashCodes, it will improve the performance of HashTables.A good distribution of hash codes will indeed help in the performance of a HashMap or Hashtable. However, by definition, hashcodes are not necessarily distinct for objects that are distinct based on equals. Two objects for which "equals" is true should have the same hashcode, but two objects which have the same hashcode don't have to have "equals" be true. There is a limited number of hashcodes (the range of int), but an unlimited number of objects. So, some objects will necessarily have the same hashcode. The pigeonhole principle describes this situation:
http://en.wikipedia.org/wiki/Pigeonhole_principle

String equal method Vs Object equal method.

hello, Can anybody explain me difference between equal method in String class and equal method in Object class. We have equal method in object classes. and object class is the super class of all classes, so why we need equal method in String class.

RGEO wrote:
hello, Can anybody explain me difference between equal method in String class and equal method in Object class. We have equal method in object classes. and object class is the super class of all classes, so why we need equal method in String class.Because "equal" means different things for different objects. For a String, "equal" would mean that both Strings being compared have the exact same characters, in the same sequence. For an Integer, "equals" would mean that both objects have the same integer value.

What is native method?

hi.. i have the following error msg on the java wireless toolkit..
"ERROR: native methods should not appear
Error preverifying class com.zucotto.io.serialcomm.COMInputStream
Build failed"
can anyone help?
thanks

You can't "un-native" a native method. The class library that you are using relies upon native code. It can not be used on the target platform. You would have to ask the vendor of that class library to update it to work on your target platform without the native code.
God bless,
-Toby Reyelts

Error calling native methods

HI
I declared a static native method in a class and using the System.loadLibrary() method i load the dll.
Now if i want to call the method from another class using instance of that class where i declare the native method, it shows an error
java.lang.SpecifiedPathLink error. I have put the dll outside the package in the same directory.
can anyone help me regarding this problem

it shows this exception
Exception in thread "main" java.lang.UnsatisfiedLinkError: no PerfMonitor in jav
a.library.path
at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1491)
at java.lang.Runtime.loadLibrary0(Runtime.java:788)
at java.lang.System.loadLibrary(System.java:834)
at C3.CPUMemoryUsage.<clinit>(CPUMemoryUsage.java:6)
at C3.Node.main(Node.java:18)

Native Method (Very Urgent).

I am working on native methods. I followed the steps as defined by the sun:
i- Create the Java Source File, containing the native method declaration:
public class NativeCode
     public native void showString();
     static
          System.loadLibrary("DisplayText");
     public static void main(String [] args)
          NativeCode nc = new NativeCode();
     nc.showString();
ii- Compile the Java Source File.
iii- use javah -jni ClassName to create Header File.
//The header file.
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class NativeCode */
#ifndef IncludedNativeCode
#define IncludedNativeCode
#ifdef __cplusplus
extern "C"
#endif
* Class: NativeCode
* Method: showString
* Signature: ()V
JNIEXPORT void JNICALL Java_NativeCode_showString
(JNIEnv *, jobject);
#ifdef __cplusplus
#endif
#endif
iv- Write the implementation of native method in "C Language", using the signature as in the Header file, generated by the javah -jni option.
// The implementation of native method in "C Language".
//NativeMethod.c
#include <jni.h>
#include "NativeCode.h"
#include <stdio.h>
JNIEXPORT void JNICALL Java_NativeCode_showString(JNIEnv *env, jobject obj)
     printf("Hello! World");
     return;
The problem is that when I compile the NativeMethod.c, the compiler generated the following errors:
i- Unable to Open include file "jni.h".
ii- Unable to Open include file "NativeCode.h"
iii- Declaration Syntax Error.
What should I do? What is the solution of this problem?
Where I have to put the "jni.h" and "NativeCode.h" files?
Please assist me in solving this problem.
Many Buckets full of thanks!

Hi
You should be able to find the jni.h in :
For Windows:
your <java_home>\include directory. jni.h also refers to jni_md.h
that should be present in <java_home>\include\win32 directory.
Copy both of them to your include path.
For Solaris:
you should find the jni.h in the same directory but jni_md.h
will be in <java_home>/include/solaris directory.
The pattern follows for other UNIX flavors too.
Hope this helps.
cheers
projyal
I am working on native methods. I followed the steps
as defined by the sun:
i- Create the Java Source File, containing the native
method declaration:
public class NativeCode
     public native void showString();
     static
          System.loadLibrary("DisplayText");
     public static void main(String [] args)
          NativeCode nc = new NativeCode();
     nc.showString();
ii- Compile the Java Source File.
iii- use javah -jni ClassName to create Header File.
//The header file.
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class NativeCode */
#ifndef IncludedNativeCode
#define IncludedNativeCode
#ifdef __cplusplus
extern "C"
#endif
* Class: NativeCode
* Method: showString
* Signature: ()V
JNIEXPORT void JNICALL Java_NativeCode_showString
(JNIEnv *, jobject);
#ifdef __cplusplus
#endif
#endif
iv- Write the implementation of native method in "C
Language", using the signature as in the Header file,
generated by the javah -jni option.
// The implementation of native method in "C
Language".
//NativeMethod.c
#include <jni.h>
#include "NativeCode.h"
#include <stdio.h>
JNIEXPORT void JNICALL
Java_NativeCode_showString(JNIEnv *env, jobject obj)
     printf("Hello! World");
     return;
The problem is that when I compile the
NativeMethod.c, the compiler generated the following
errors:
i- Unable to Open include file "jni.h".
ii- Unable to Open include file "NativeCode.h"
iii- Declaration Syntax Error.
What should I do? What is the solution of this
problem?
Where I have to put the "jni.h" and "NativeCode.h"
files?
Please assist me in solving this problem.
Many
Many Buckets
Many Buckets full of thanks!

Testing ActionScript classes with native methods?

Hi,
I have an ActionScript class that I'm writing and would like to test using FlexUnit.
The only issue is that the ActionScript class has a member in it that is a class with native methods.
So, I get the following error when trying to run a test of that ActionScript class:
VerifyError: Error #1079: Native methods are not allowed in loaded code.
Does anyone know of a way to get around this? FlexUnit seems not to like native methods being present.
Thanks,
Matt

Hi casdvm,
by definition, you only own objects that you created using one of the alloc* methods, copy: or new:. All other objects (IIRC with a few noted exceptions) are autoreleased.
If you create convenience methods in your own class, you should follow the same rule. For example, if you have a class Pet and want to implement the method +petWithName, your code might look something like that:
+ petWithName: (NSString *)name
return [[[Pet alloc] initWithName: name] autorelease];
Alex

Access object attributes using other object JNI native method

Hi. I'm trying to change an attribute of object O1 from another object O2 without invoking a O1 method and without making the attribute as public or protected.
The only possibility that comes to my mind for doing so is writting a JNI native method
public class O1 {
static public native changeAttribute (Object O2, Object newAttributeValue) ;
that change the attribute memory reference, but all I've found about accesing attributes in JNI is about accessing the invoker attributes (in this case, O1).
�Does any one know if it's possible to do so? Thanks.

I know that is not a good practice but I cannot figure out another way.
I'll try to explain the whole problem so you see the reason. I'm working with transactions, using objects as the data. An object can be opened for write by several transactions because the granularity for conflicts is not the object, is each of its attributes. As long as two transaction don't write the same attribute, they both can write. For writing, each transactions uses a private copy of the object. At committing, the actual copy of the object must be replaced by the committer one, but as far as the granularity is the object attributes, only each written attribute must be replaced (if not, only the last commit would be visible).
This attribute replace must be done by the transaction manager as far as the transactional object is provided by the client. So what i was thinking was to use JNI or some trick like that to replace the object attributes transparently to the object.
I hope the explain is clear, my english is a little asleep :-(.
How to do it with reflection? I thought that was only for method calling. Anyway, there wouldn't be problems if the attributes are private?
Thanks for answering.
EDIT: I've been able to change a public field using reflection, but not the private one
import java.lang.reflect.*;
class Caca {
public static void main(String[] args) {
Integer r = new Integer(0);
System.out.println("original: " + r.toString());
modifyWidth(r, 300);
System.out.println("modified: " + r.toString());
static void modifyWidth(Integer r, int newValue ) {
Field valueField; Class c = r.getClass();
try {
valueField = c.getField("value");
valueField.set(r, newValue);
} catch (Exception e) { System.out.println(e); }
Message was edited by:
dfasdfsdafsadfasdf

Native method in object class........

Similar Messages

Maybe you are looking for