Native keyword in java

native keyword in java

The » native « keyword can be applied to a method to indicate that the method is implemented in a language other then Java such as C or C++.

When a method is marked as native , it can not have a body and should end with a semicolon.

The Java Native Interface is responsible for writing Java native methods and embedding the JavaTM virtual machine into native applications.

Example

public class JavaNativeExample

Now add(int num1,int num2) method is defined in native language other than Java either in C or C++ but it can be called in Java code using the object of above class as below

JavaNativeExample nativeEx = new JavaNativeExample(); int res = nativeEx.add(10,20);

Native methods are usually used to interface with system calls or libraries written in other programming languages.

Please look at the below link for more details on JNI

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Native keyword in Java

The native keyword acts as a link between the JAVA language and a chunk of code or library written in different languages except for JAVA, which may depend on the machine you are operating on. If the native keyword is applied to a method, then that means the method will be implemented using native code written in some other language (like C or C++) via JNI (JAVA native interface).

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Syntax of Native Keyword in Java

The syntax of native code is the same as the normal function definition, with the “native” keyword added at the starting of the function.

For example:

Here the public is an access modifier. It should be public so that another file can use it. The string is the return data type of the function. It can be integer, character or Boolean depending upon the keyword. The parameter passed to this function is of data type string as well. Everything should be kept underclass.

After function declaration, we call this function via object created, and library loaded.

public static void main(String[] args)

Library defined above should be loaded first, and the n its object is created. With the help of this object, the native function is called.

How does the Native keyword work?

There should be two files. One containing JAVA code, while the other one should have C/C++ legacy code. Java code will be used to call the legacy code. This legacy code will interact with hardware and return the expected output.

When the legacy code interacts with hardware, then it will not follow the guidelines laid out by JAVA. This code will do the desired processing to get the output and pass the results to JNI. Java native interface will then check in its directory containing all the rules pertaining to native code (This comes under a file called javah.exe in SDK). JNI is designed as part of the Java toolkit. After this processing, the JAVA will publish the outputs in the JAVA language itself. When we are creating the JAVA program, we must make sure that there is a variable/ data flow link between the JAVA file and the legacy file so that there is a smooth flow of data between both.

Steps explaining how to make use of native keywords are given below:

1. Write the JAVA code containing the native method, shared library loaded and save it using “filename.JAVA”.
2. Compile JAVA code and convert the code to bytecode.
3. Create a C/C++ header file containing a native function signature which should be called.
4. Write C/C++ code has a native method’s implementation.
5. Run JAVA executable file to see the results.

Example

We should write code in Eclipse and run the code to create a library using which then C code will be implemented.

Code: package com.slackerOne;

public class JPP < public static native void pAccess(); public static native int pRead(); public static native void pWrite(int port, int output); static< System.loadLibrary("JPPlibs"); >public void jAccess() < JPP.pAccess(); >public int jRead() < return JPP.pRead(); >public void jWrite(int port, int output) < JPP.pWrite(port, output); >>

After saving this code in the new “class” of the java project, we have to set up a run environment to generate a header file.

When we will run this, we should get a library generated.

Here we created the header file from the java code, which will link native code and java language.

Advantages of Native Keyword in Java

Given below are some of the advantages.

1. It provides an added advantage to JAVA to interact with the code written in other languages and reduce the work to have the same code written in JAVA, hence reducing the code redundancy.
2. It improves the overall code performance. As the code is written in other languages, it may be faster when it works with the machine language than JAVA. We can then use the JAVA program to call this code.
3. Using this approach, we can directly give system calls. Reducing the probability of external interference and improving the sped of code execution.
4. You can dynamically call a pre-loaded library (written in any language other than JAVA) using an arbitrary driving code written in JAVA and still get a response in JAVA.
5. It makes it accessible for JAVA to reach the hardware resources which are available to be used by other languages only.
6. In case you have a platform-dependent code already build-up for your application, and whose features are not supported via JAVA, in that case, we can have native code and link this native code to JAVA via native keyword.

Rules

The rules for a native keyword are as follows.

1. The native keyword is to be used before the method name.
2. Native method declaration does not have a body and should end with a semicolon as these methods are not defined in JAVA but are present in the C/C++ language.
3. Native methods can not be declared as abstract method.
4. Since there is no surety if the previous old code is written in accordance to IEEE 754 standard (The IEEE Standard for Floating-Point Arithmetic is a technical standard for floating-point arithmetic established in 1985 by the Institute of Electrical and Electronics Engineers) so, we can not declare these native methods as strictftp.
5. JAVA designs the Java Native Interface (JNI) specification to define the rules and declarations to implement native methods, like conversion of data types between Java and the native code.

Conclusion

The native keyword is which bridges the gap between native languages and JAVA. This can be used as a critical link if our software’s interaction with hardware is more efficient in using pre-existing code. It makes the implementation work lesser in comparison to designing a new application code from scratch wherever it could be avoided.

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Использование ключевого слова native в Java

Часто при изучении Java возникает вопрос о назначении и использовании ключевого слова native . Это ключевое слово используется, когда необходимо вызвать метод, который не написан на Java, а написан на другом языке программирования, таком как C или C++.

Примером может служить ситуация, когда разработчику требуется использовать некоторые низкоуровневые возможности операционной системы или вызвать функцию, которая была написана на другом языке программирования. В этом случае, в Java-коде объявляют метод с ключевым словом native , и этот метод будет связан с некоторой функцией, написанной на другом языке программирования, через Java Native Interface (JNI).

public class NativeExample

В приведенном выше примере exampleMethod — это нативный метод, который должен быть реализован на другом языке программирования.

Следует заметить, что использование ключевого слова native и JNI должно быть оправдано, так как это увеличивает сложность кода и может привести к проблемам с переносимостью приложения. Обычно такой подход используется, когда Java не предоставляет необходимых возможностей или когда требуется повысить производительность приложения за счет использования нативного кода.

В заключение, ключевое слово native в Java используется для объявления нативных методов, то есть методов, которые реализованы на другом языке программирования. Это позволяет разработчикам использовать функции и возможности, которые не доступны или неэффективны в Java.

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Java Guides

The native keyword is applied to a method to indicate that the method is implemented in native code using JNI (Java Native Interface).

Key points about native Java Keyword

1. The native keyword may be applied to a method to indicate that the method is implemented in a language other than Java.
2. The native keyword is used to declare a method which is implemented in platform-dependent code such as C or C++. When a method is marked as native, it cannot have a body and must ends with a semicolon instead.
3. The Java Native Interface (JNI) specification governs rules and guidelines for implementing native methods, such as data type conversion between Java and the native application.

native Java Keyword Example

1. Main.java

public class Main < public native int square(int i); public static void main(String[] args) < System.loadLibrary("Main"); System.out.println(new Main().square(2)); > >

2. Main.c:

#include #include "Main.h" JNIEXPORT jint JNICALL Java_Main_square( JNIEnv *env, jobject obj, jint i)

3. Compile and run:

sudo apt-get install build-essential openjdk-7-jdk export JAVA_HOME='/usr/lib/jvm/java-7-openjdk-amd64' javac Main.java javah -jni Main gcc -shared -fpic -o libMain.so -I$/include \ -I$/include/linux Main.c java -Djava.library.path=. Main 

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