java NPE就是空指针异常,null pointer exception…

先来看一下JDK1.6的API: NullPointerException (Java Platform SE 6) public class NullPointerException extends RuntimeExceptionnull 当应用程序试图在需要对象的地方使用时,抛出该异常.这种情况包括: * 调用 null 对象的实例方法. * 访问或修改 null 对象的字段. * 将 null 作为一个数组,获得其长度. * 将 null 作为一个数组,访问或修改其时间片. * 将 nu…

这么一件小事折腾了一个多小时,google也上不去,对百度我就不吐槽什么了,最后用bing查出了满意的结果.一般程序中不要显式把jsp.jar和servlet.jar放在Lib目录下,因为tomcat目录下自带,如果添加进去反而会冲突.但是eclipse中不把两个包放进去又编译不通过,这只要用eclipse导入这两个包就可以了.…

本文转载自:https://blog.csdn.net/hpu11/article/details/72628052 这说明是非法指针的使用,才导致系统出错. [ 1023.510000] Unable to handle kernel NULL pointer dereference at virtual address 00000000[ 1023.520000] pgd = c0004000[ 1023.520000] [00000000] *pgd=00000000[ 1023.5200…

通过这个简单的案例,手把手教给你分析异常信息(适合初学者看) org.springframework.dao.InvalidDataAccessApiUsageException: The given id must not be null!; nested exception is java.lang.IllegalArgumentException: The given id must not be null! at org.springframework.orm.jpa.EntityMan…

Null Reference Exception : Object reference not set to an instance of an object. 异常:空引用,对象的引用未设置到对象的实例. 出现该异常的位置: 可能是在调用组件时该组件还未实例化或未存储地址指针,需要查看是否将组件位置拽入代码公布的字段:还有注意Unity3D的生命周期,调整代码的执行顺序. (若有错误和不足之处,还望指正,谢谢!)    …

// Note: //int x = a[0].GetInt(); // Error: operator[ is ambiguous, as 0 also mean a null pointer of const char* type. int y = a[SizeType(0)].GetInt(); // Cast to SizeType will work. int z = a[0u].GetInt(); // This works too. 0u = SizeType(0)   Json:…

在Joshua Bloch很有名的一本书<Effective in java>中建议不要在代码中返回空的collection/map/array,就像下面的代码一样: public List<String> returnCollection() { //remainder omitted if (/*some condition*/) { return null; } else { // return collection }} 而应该使用下面的模式: public List<…

These are two different concepts, you cannot compare them. What the difference between the skunk and the moonlight? Null pointer is a special reserved value of a pointer. A pointer of any type has such a reserved value. Formally, each specific pointe…

参考: LEETCODE 中的member access within null pointer of type 'struct ListNode' 解决 leetcode 编译问题:Line x: member access within null pointer of type 'struct TreeNode' 在leetcode上提交代码后出现编译错误: Line x: member access within null pointer of type 'struct TreeNode'…