What is native method in java with example

What is native in Java with example?

The native keyword is applied to a method to indicate that the method is implemented in native code using JNI (Java Native Interface). native is a modifier applicable only for methods and we can’t apply it anywhere else. The methods which are implemented in C, C++ are called as native methods or foreign methods.

What is native in Java class?

A native method is a Java method (either an instance method or a class method) whose implementation is also written in another programming language such as C/C++. Moreover, a method marked as native cannot have a body and should end with a semicolon: [ public | protected | private] native [return_type] method ();

What is native function in Java?

Native methods are Java™ methods that start in a language other than Java. Native methods can access system-specific functions and APIs that are not available directly in Java. The use of native methods limits the portability of an application, because it involves system-specific code.

Why hashCode method is native in Java?

The methods are native because they concern native data. The hashCode method returns an integer value dependent on the internal representation of a pointer to an object on the heap. The getClass method must access the internal vtbl (virtual function table) that represents the compiled program’s class hierarchy.

What are native functions?

Native functions are declared with SPL syntax in XML function model files, but native function implementations are defined in a native file. An example native function prototype is: T max(list) This example declares a generic max function that works on lists of any ordered type T .

How do I find my native code?

If instead you want to add native code to an existing project, you need to follow these steps:

1. Create new native source files and add them to your Android Studio project.
2. Configure CMake to build your native source code into a library.
3. Configure Gradle by providing a path to your CMake or ndk-build script file.

When do you use native methods in Java?

It marks a method, that it will be implemented in other languages, not in Java. It works together with JNI (Java Native Interface). Native methods were used in the past to write performance critical sections but with Java getting faster this is now less common. Native methods are currently needed when

What does the native keyword mean in Java?

native keyword in java. The native keyword is applied to a method to indicate that the method is implemented in native code using JNI (Java Native Interface). native is a modifier applicable only for methods and we can’t apply it anywhere else. The methods which are implemented in C, C++ are called as native methods or foreign methods.

When to use a local variable in Java?

You can use this variable only within that method and the other methods in the class aren’t even aware that the variable exists. A local variable cannot be defined with “static” keyword. A variable declared inside the class but outside the body of the method, is called instance variable.

Which is the native interface for Java programming?

Java supports native codes via the Java Native Interface (JNI). JNI is difficult, as it involves two languages and runtimes. I shall assume that you are familiar with: Java. C/C++ and the GCC Compiler (Read ” GCC and Make “). (For Windows) Cygwin or MinGW (Read ” How to Setup Cygwin and MinGW “). 2. Getting Started

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Write Native Methods in Java

1. What Are Native Methods in Java
2. Write Native Methods in Java Programs

This article takes you through various steps necessary to learn how to write native methods in Java programs.

What Are Native Methods in Java

The native keyword is a modifier in Java programming, used with methods only. It represents that this particular method is written in the native code via Java Native Interface (JNI).

The native (or foreign) methods are implemented in C, C++, or any other platform-dependent code.

[public/protected/private] native [returnType] youMethodName(); 

Write Native Methods in Java Programs

Listed below is the multi-step process to write native methods in Java programs:

Write the Java program containing the native method’s declaration and the main method to call the native method.

Compile the Java program with the main method and declare the specified native method.

Use javah with -jni flag to create the header file for the native method.

Write the code for the native method in the programming language you like, for instance, C/C++.

Create the shared library to compile the implementation and header files.

Finally, execute/run the Java Program.

Let’s follow all of these steps to call native methods in the Java program.

Write a Java Program

class nativeDemoClass  //declaration of the native method  public native void showMessage();   //load native C library  static  System.loadLibrary("nativedemoclass"); //lowercase of classname  >   //java main method  public static void main (String[] args)  nativeDemoClass demo = new nativeDemoClass();  demo.showMessage();  > > 

We must include the native keyword as a method’s declaration part in the Java program if we implement the method in a programming language other than Java.

This native keyword tells the Java compiler that this specific method is a native programming language method. Remember, the declaration of a native method in the Java program provides the method signature only.

We have a static block that loads the native C library in which we have written the implementation of the showMessage() method. Have you noticed that we are passing a string to the System.loadLibrary() method?

Why is it so? It is because this static block from the nativeDemoClass class will load the appropriate library, named nativedemoclass .

Let’s move to the second step and compile the Java program.

Compile the Java Program

Use the command given below to compile the Java program.

javac nativeDemoClass.java 

After successfully compiling the Java program, we get the nativeDemoClass.class file.

Create a Header File

Use the following command to create a header file.

Here, -h produces the C/C++ header files and places the generated file into the specified directory. We use dot ( . ) to keep the generated header file in the current directory.

javac -h . nativeDemoClass.java 

You may find on the Internet that javah creates C/C++ header files, which was correct until JDK 8. According to the oracle, javah is deprecated now, but we have an alternative solution given above.

The nativeDemoClass.h file looks as follows. We do not edit this because it is a machine-generated file.

/* DO NOT EDIT THIS FILE - it is machine generated */ #include  /* Header for class nativeDemoClass */  #ifndef _Included_nativeDemoClass #define _Included_nativeDemoClass #ifdef __cplusplus  extern "C"  #endif  /* * Class: nativeDemoClass * Method: showMessage * Signature: ()V */ JNIEXPORT void JNICALL Java_nativeDemoClass_showMessage  (JNIEnv *, jobject);  #ifdef __cplusplus  > #endif #endif 

The JNIEXPORT void JNICALL Java_nativeDemoClass_showMessage declares the C function in this header file. We can have multiple function signatures if the nativeDemoClass has more native methods.

• Prefix as Java_
• The package name
• The class name
• native method’s name

Each section is separated by an underscore ( _ ), as shown graphically below:

Further, the JNIEnv* refers to the Java Native Interface environment that allows us to access the Java Native Interface (JNI) methods. The jobject references this object of Java programming.

Write the Native Code

#include #include "nativeDemoClass.h" #include  JNIEXPORT void JNICALL Java_nativeDemoClass_showMessage(JNIEnv *env, jobject obj)   printf("Hello world!\n");  return; > 

The implementation of Java_nativeDemoClass_showMessage is pretty straightforward because we are only using a printf() statement to print Hello world . Remember, this .c file has three headers, jni.h , stdio.h , and nativeDemoClass.h created in the previous step.

Create the Shared Library

Use the following command to create the shared library. We must have build tools for visual studio to use the CL command.

cl -Ic:\java\jdk-17.0.2\include -Ic:\java\jdk-17.0.2\include\win32 -LD nativeDemoClassImp.c -Fenativedemoclass.dll 

Remember, the Java program uses the following method to load the shared library, named nativedemoclass at run time.

System.loadLibrary("nativedemoclass"); 

Run the Java Program

Finally, use the command given below to run the Java program.

You will see Hello world! on the command line if you have done everything correctly.

Mehvish Ashiq is a former Java Programmer and a Data Science enthusiast who leverages her expertise to help others to learn and grow by creating interesting, useful, and reader-friendly content in Computer Programming, Data Science, and Technology.

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