本篇結(jié)構(gòu)：
- 簡介
- 實(shí)例
一悠砚、簡介
接JNI簡介的基礎(chǔ)上背捌，新增訪問實(shí)例域的例子癌刽。
訪問和修改實(shí)例變量操作步聚：
調(diào)用 GetObjectClass 函數(shù)獲取實(shí)例對(duì)象的 Class 引用
調(diào)用 GetFieldID 函數(shù)獲取 Class 引用中某個(gè)實(shí)例變量的 ID
調(diào)用 GetXXXField 函數(shù)獲取變量的值，需要傳入實(shí)例變量所屬對(duì)象和變量 ID
調(diào)用 SetXXXField 函數(shù)修改變量的值步绸，需要傳入實(shí)例變量所屬對(duì)象掺逼、變量 ID 和變量的值訪問和修改靜態(tài)變量操作步聚：
調(diào)用 FindClass 函數(shù)獲取類的 Class 引用
調(diào)用 GetStaticFieldID 函數(shù)獲取 Class 引用中某個(gè)靜態(tài)變量 ID
調(diào)用 GetStaticXXXField 函數(shù)獲取靜態(tài)變量的值，需要傳入變量所屬 Class 的引用和變量 ID
調(diào)用 SetStaticXXXField 函數(shù)設(shè)置靜態(tài)變量的值瓤介，需要傳入變量所屬 Class 的引用吕喘、變量 ID和變量的值
二、實(shí)例
2.1惑朦、編寫java類
public class Employee {
private String name;
private double salary;
static {
System.loadLibrary("Employee");
}
public native void raiseSalary(double byPercent);
public Employee(String n, double s){
this.name = n;
this.salary = s;
}
public void print(){
System.out.println(name + " " + salary);
}
}
public class EmployeeTest {
public static void main(String[] args) {
Employee[] staff = new Employee[3];
staff[0] = new Employee("Tom", 35000.0);
staff[1] = new Employee("Bob", 11000.0);
staff[2] = new Employee("Jane", 9999.0);
for (Employee e : staff) {
e.raiseSalary(5);
}
for (Employee e : staff) {
e.print();
}
}
}
2.2兽泄、編譯java類
javac Employee.java
javac EmployeeTest.java
2.3、生成相關(guān)JNI方法的頭文件
javah -d jnilib -jni Employee
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class Employee */
#ifndef _Included_Employee
#define _Included_Employee
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: Employee
* Method: raiseSalary
* Signature: (D)V
*/
JNIEXPORT void JNICALL Java_Employee_raiseSalary
(JNIEnv *, jobject, jdouble);
#ifdef __cplusplus
}
#endif
#endif
2.4漾月、使用C/C++實(shí)現(xiàn)本地方法
#include "Employee.h"
#include <stdio.h>
JNIEXPORT void JNICALL Java_Employee_raiseSalary(JNIEnv* env, jobject this_obj, jdouble byPercent){
/* get the class */
jclass class_Employee = (*env)->GetObjectClass(env, this_obj);
/* get the field Id */
jfieldID id_salary = (*env)->GetFieldID(env, class_Employee, "salary", "D");
/* get the field value */
jdouble salary = (*env)->GetDoubleField(env, this_obj, id_salary);
salary *= 1 + byPercent/100;
/* set the field value */
(*env)->SetDoubleField(env, this_obj, id_salary, salary);
}
jfieldID id_salary = (*env)->GetFieldID(env, class_Employee, "salary", "D");中D代表類型double病梢。
2.5、生成動(dòng)態(tài)鏈接庫
gcc -D_REENTRANT -fPIC -I $JAVA_HOME/include -I $JAVA_HOME/include/linux -shared -o libEmployee.so Employee.c
2.6梁肿、運(yùn)行java
最后運(yùn)行蜓陌。
