What is native keyword in Java

Native keyword in Java
In Java, the native keyword indicates that a method is implemented by an external language, that is, the implementation of the method is written in other languages. It tells the Java compiler that the implementation of the method is not in the current Java program and needs to be implemented by interacting with the Java Virtual Machine (JVM).

Why is there the native keyword?
Java is an object-oriented programming language that provides many powerful class libraries and frameworks for developers to use. However, some specific operations or functions, such as the underlying operations of the operating system, direct access to hardware, calling functions of other programming languages, etc., are beyond the scope of Java. To be able to use these features, Java introduced the native keyword.

How to use the native keyword?
In Java, methods using the native keyword must be non-private, non-static instance methods, and cannot have a method body. The declaration of a native method must have a corresponding interface with the Java code that calls it. This interface is called a native method interface (JNI).

Sample code:
The following is a simple example illustrating how to use the native keyword.

public class NativeExample {
   // 声明native方法
   public native void nativeMethod();

   // 静态代码块，加载本地库
   static {
      System.loadLibrary("NativeLibrary");
   }

   // 主方法
   public static void main(String[] args) {
      // 创建本地示例对象
      NativeExample example = new NativeExample();
      // 调用native方法
      example.nativeMethod();
   }
}

The above code demonstrates a Java class named NativeExample. Among them, the nativeMethod() method is declared as a native method and has no method body. In the static code block, we loaded a native library called NativeLibrary using the System.loadLibrary() method.

In the main() method, we created the instance object example of NativeExample and called the nativeMethod() method. Since the implementation of the nativeMethod() method is not in the Java program, the program will interact with the local library through JNI and execute the code corresponding to the nativeMethod() method in the local library.

It should be noted that the method using the native keyword needs to be implemented through JNI, which requires us to write the corresponding method body in other languages ​​such as C/C.

Summary:
By using the native keyword, Java programs can call functions implemented in other programming languages, thereby expanding the capabilities and flexibility of Java. However, when using the native keyword, you need to pay attention to declaring the function body corresponding to the native method in the native method interface (JNI), and loading the native library correctly to ensure that the program can call and execute native code normally.

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