如何解决Java中线程主NoClassDefFoundError中的异常？

Question

我第一次处理Java Annotations。如果我做错了什么，请原谅我！但是这个类使用 javac MyFirstAnnotation.java 成功编译 但是当我尝试使用 java TestMyAnnotation

运行此源代码时

它会抛出这样的错误

包注释;

import java.lang.annotation.*;
import java.util.*;
import java.lang.reflect.*;

@Documented
@Target(ElementType.METHOD)
@Inherited
@Retention(RetentionPolicy.RUNTIME)

public @interface MyFirstAnnotation
{   
String author() default "Chiranjib Nandy";
int revisionNumber() default 1;
String date();
}

class MySuperClass 
{   
public String showMe()
{
    return "Do Something";
}
}

class MyAnnotation extends MySuperClass
{
@Override
@MyFirstAnnotation(author="Recmach",revisionNumber=2,date="1st June,2014")
public String showMe()
{
    return "Display Something";
}

@Deprecated
@MyFirstAnnotation(revisionNumber=2,date="2nd June,2014")
public void oldMethod() 
{
    System.out.println("It is a deprecated method");
}

@SuppressWarnings({"unused","deprecation"})
@MyFirstAnnotation(author="Papai",date="1st June,2014")
public void myMethod()
{
    int j;
    oldMethod();
    System.out.println("It is defined in my way");
}
}

class TestMyAnnotation
{
public static void main(String[] args) throws ClassNotFoundException
{
    Method myMethods[]=Class.forName("Annotations.MyAnnotation").getDeclaredMethods();
    for(Method m : myMethods)
    {
        Annotation[] annotations=m.getDeclaredAnnotations();
        for(Annotation anno : annotations)
        {
            if(anno  instanceof MyFirstAnnotation)
            {
                MyFirstAnnotation myFirstAnnotation = (MyFirstAnnotation) anno;
                System.out.println("name : "+myFirstAnnotation.author());
                System.out.println("name : "+myFirstAnnotation.revisionNumber());
                System.out.println("name : "+myFirstAnnotation.date());
            }
        }
    }
}
}

Answer 1

希望此链接有所帮助。

http://www.shivasoft.in/blog/java/compile-and-run-java-program-in-package-from-command-line/

这已经在堆栈溢出。您必须使用此文章中的包编译您的课程。

Answer 2

我修复了三个问题。

1. public课程必须为TestMyAnnotation。

2. 这一行应该是MyAnnotation，而不是之前的

   Method myMethods[]=Class.forName("MyAnnotation").getDeclaredMethods();
   

3. 顶部的第一个类不应该是public，因为一个文件中不能有两个公共类。

使用以下代码并将其放在TestMyAnnotation.java中。然后运行javac TestMyAnnotation.java，然后运行java TestMyAnnotation。

import java.lang.annotation.*;
import java.util.*;
import java.lang.reflect.*;

@Documented
@Target(ElementType.METHOD)
@Inherited
@Retention(RetentionPolicy.RUNTIME)

@interface MyFirstAnnotation
{   
String author() default "Chiranjib Nandy";
int revisionNumber() default 1;
String date();
}

class MySuperClass 
{   
public String showMe()
{
    return "Do Something";
}
}

class MyAnnotation extends MySuperClass
{
@Override
@MyFirstAnnotation(author="Recmach",revisionNumber=2,date="1st June,2014")
public String showMe()
{
    return "Display Something";
}

@Deprecated
@MyFirstAnnotation(revisionNumber=2,date="2nd June,2014")
public void oldMethod() 
{
    System.out.println("It is a deprecated method");
}

@SuppressWarnings({"unused","deprecation"})
@MyFirstAnnotation(author="Papai",date="1st June,2014")
public void myMethod()
{
    int j;
    oldMethod();
    System.out.println("It is defined in my way");
}
}

public class TestMyAnnotation
{
public static void main(String[] args) throws ClassNotFoundException
{
    Method myMethods[]=Class.forName("MyAnnotation").getDeclaredMethods();
    for(Method m : myMethods)
    {
        Annotation[] annotations=m.getDeclaredAnnotations();
        for(Annotation anno : annotations)
        {
            if(anno  instanceof MyFirstAnnotation)
            {
                MyFirstAnnotation myFirstAnnotation = (MyFirstAnnotation) anno;
                System.out.println("name : "+myFirstAnnotation.author());
                System.out.println("name : "+myFirstAnnotation.revisionNumber());
                System.out.println("name : "+myFirstAnnotation.date());
            }
        }
    }
}
}

Answer 3

尝试运行您的Main Java类，添加-cp（类路径），如下面的命令：

java -cp . TestMyAnnotation

希望它有所帮助。