null

问题 Consider the custom toString() implementation of a bean: @Override public String toString() { String.format("this is %s", this.someField); } This yields this is null if someField is null. Is there a way to override the default null string representation of null-valued arguments to another text, i.e., ? without calling explicitly replaceAll(...) in the toString method? Note : The bean inherits from a superclass that could implement Formattable (http://docs.oracle.com/javase/7/docs/api/java

问题 Is this behavior defined or not? volatile long (*volatile ptr)[1] = (void*)NULL; volatile long v = (long) *ptr; printf("%ld\n", v); It works because by dereferencing pointer to array we are receiving an array itself, then that array decaying to pointer to it's first element. Updated demo: https://ideone.com/DqFF6T Also, GCC even considers next code as a constant expression: volatile long (*ptr2)[1] = (void*)NULL; enum { this_is_constant_in_gcc = ((void*)ptr2 == (void*)*ptr2) }; printf("%d\n",

问题 This question's answers are a community effort . Edit existing answers to improve this post. It is not currently accepting new answers or interactions. I have some code and when it executes, it throws a NullReferenceException , saying: Object reference not set to an instance of an object. What does this mean, and what can I do to fix this error? 回答1: What is the cause? Bottom Line You are trying to use something that is null (or Nothing in VB.NET). This means you either set it to null , or

问题 I am trying to return the data in the spreadsheet to an Apps Script published as a webApp. However, for one of my spreadsheets (link), the returned data is null . I logged the the data before returning to make sure that it isn't null, and I can see them in the logs. This is my code: function doGet(){ return HtmlService.createHtmlOutputFromFile('index'); } function spreadsheetTest() { var ss = SpreadsheetApp.getActiveSpreadsheet(); var sheet = ss.getSheetByName("Sheet1"); var maxRows = sheet

问题 I am trying to return the data in the spreadsheet to an Apps Script published as a webApp. However, for one of my spreadsheets (link), the returned data is null . I logged the the data before returning to make sure that it isn't null, and I can see them in the logs. This is my code: function doGet(){ return HtmlService.createHtmlOutputFromFile('index'); } function spreadsheetTest() { var ss = SpreadsheetApp.getActiveSpreadsheet(); var sheet = ss.getSheetByName("Sheet1"); var maxRows = sheet

问题 I need to mix "record" type with null type in Schema. "name":"specShape", "type":{ "type":"record", "name":"noSpecShape", "fields":[ { "name":"bpSsc", "type":"null", "default":null, "doc":"SampleValue: null" },... For example, for some datas specShape may be null. So if I set type to "name":"specShape", "type":{ **"type":["record", "null"],** "name":"noSpecShape", "fields":[ { "name":"bpSsc", "type":"null", "default":null, "doc":"SampleValue: null" },... it says No type: {"type":["record",

问题 I need to mix "record" type with null type in Schema. "name":"specShape", "type":{ "type":"record", "name":"noSpecShape", "fields":[ { "name":"bpSsc", "type":"null", "default":null, "doc":"SampleValue: null" },... For example, for some datas specShape may be null. So if I set type to "name":"specShape", "type":{ **"type":["record", "null"],** "name":"noSpecShape", "fields":[ { "name":"bpSsc", "type":"null", "default":null, "doc":"SampleValue: null" },... it says No type: {"type":["record",

问题 I need to mix "record" type with null type in Schema. "name":"specShape", "type":{ "type":"record", "name":"noSpecShape", "fields":[ { "name":"bpSsc", "type":"null", "default":null, "doc":"SampleValue: null" },... For example, for some datas specShape may be null. So if I set type to "name":"specShape", "type":{ **"type":["record", "null"],** "name":"noSpecShape", "fields":[ { "name":"bpSsc", "type":"null", "default":null, "doc":"SampleValue: null" },... it says No type: {"type":["record",

问题 The book Understanding and Using C Pointers , by Richard Reese says: The null concept is an abstraction supported by the null pointer constant. This constant may or may not be a constant zero. A C programmer need not be concerned with their actual internal representation. My question is, since "this constant may or may not be a constant zero," is it safe for me to do things like the below in my code: int *ptr = NULL; // Some code which probably sets ptr to a valid memory address if(!ptr) {

问题 The book Understanding and Using C Pointers , by Richard Reese says: The null concept is an abstraction supported by the null pointer constant. This constant may or may not be a constant zero. A C programmer need not be concerned with their actual internal representation. My question is, since "this constant may or may not be a constant zero," is it safe for me to do things like the below in my code: int *ptr = NULL; // Some code which probably sets ptr to a valid memory address if(!ptr) {