测试文件：hello-jni/src/com/example/hellojni/HelloJni.java

/**
 * 该文件来自 Android NDK Sample - HelloJni， 为了便于说明问题，我作了一些修改。
 */
package com.example.hellojni;

public class HelloJni
{
    public native String  stringFromJNI();

    public native String  unimplementedStringFromJNI();

    static {
        System.loadLibrary("hello-jni");
    }
}

错误一

david@xmomx:hellojni$ javac HelloJni.java 
david@xmomx:hellojni$ ls
Hello.class  Hello.h  Hello.java  HelloJni.class  HelloJni.java
david@xmomx:hellojni$ javah -jni HelloJni
error: cannot access HelloJni
bad class file: ./HelloJni.class
class file contains wrong class: com.example.hellojni.HelloJni
Please remove or make sure it appears in the correct subdirectory of the classpath.
com.sun.tools.javac.util.Abort
	at com.sun.tools.javac.comp.Check.completionError(Check.java:164)
	at com.sun.tools.javadoc.DocEnv.loadClass(DocEnv.java:149)
	at com.sun.tools.javadoc.RootDocImpl.<init>(RootDocImpl.java:77)
	at com.sun.tools.javadoc.JavadocTool.getRootDocImpl(JavadocTool.java:159)
	at com.sun.tools.javadoc.Start.parseAndExecute(Start.java:330)
	at com.sun.tools.javadoc.Start.begin(Start.java:128)
	at com.sun.tools.javadoc.Main.execute(Main.java:66)
	at com.sun.tools.javah.Main.main(Main.java:147)
javadoc: error - fatal error
2 errors

错误原因，没有在正确的路径下执行 javah 命令，应该在源码根目录下执行。

错误二:

david@xmomx:hellojni$ cd ../../../
david@xmomx:src$ ls
com
david@xmomx:src$ javah -jni HelloJni
error: cannot access HelloJni
class file for HelloJni not found
javadoc: error - Class HelloJni not found.
Error: No classes were specified on the command line.  Try -help.

错误原因：Classes 参数要使用完整类名，也就是说要加上包名

错误四：

david@xmomx:src$ javah -jni com/example/hellojni/HelloJni
javadoc: error - Illegal package name: "com/example/hellojni/HelloJni"
1 error

错误原因：完整类名格式错误

david@xmomx:src$ javah -jni com.example.hellojni.HelloJni

OK，编译通过。

如果还有错误，说是类找不到还是什么的，请尝试添加 -classpath . 参数。如下：

david@xmomx:src$ javah -jni -classpath . com.example.hellojni.HelloJni