替换空变量或未设置的变量。
为空变量设置一个默认值。
如果用户名和密码的其他两个来源为空，并且在每次使用后不能重新设置，则只能使用这些实例变量，所以每个请求都可能会使用它们。
These instance variables are only used if the other two sources of username and password are null, and are not reset after each use, so they can potentially be used on every request.
如果远程数据源不能处理主机变量或参数标记符中的NULL，那么任何需要绑定一个可以为空的值的函数都必须在本地计算。
If the remote data source cannot handle the null value in a host variable or parameter marker, any function that involves binding a nullable value has to be evaluated locally.
当队列是空的时候，读线程现在并不抛出异常，而是在条件变量上阻塞自身。
Instead of throwing an exception when the queue is empty, the reader thread now blocks itself on the condition variable.
如果用空的初始化器列表对变量进行初始化，对象为初始化值。
If a variable is initialized with an empty initializer list, the object is value initialized.
错误可以发生在首个测试期间，并阻止您去设置变量的值，并导致其他的测试接受一个空值。
An error could occur in the first test and prevent the variable's value from being set, thus resulting in the other tests receiving a null value.
如果字符串非空，它就包含请求的变量值。
If the string is not empty it will contain the value of the variable requested.
如果从数据库返回了一行，则使用非空的用户名和密码成员变量来填充userbean。
If a row is returned from the database, the UserBean is populated with non-null user name and password member variables.
如果viewforward为空，那么在execute方法中会将这一变量设置为failure。
If viewForward is null, this variable is set to failure in the execute method.
否则，Shell将把尾随文本解释为变量名称的一部分——并且很可能返回一个空值。
Otherwise, the shell interprets the trailing text as part of your variable name — and most likely returns a null value.
在对read方法的第二个调用中，试图把值分配给str变量，结果返回一个空的string。
The second call to the read method, where you try to assign the value to the str variable, returns an empty string.
这些实例变量不能重新设置，如果它们不为空，则用于为每个请求提供用户名和密码。
These instance variables are not reset and, if they are not null, are used to provide the username and password on every request.
如果产生了异常，那么就会对那个限定了作用域的变量进行赋值：如清单18中的EL表达式所显示的那样，该变量的值将不会为空。
If an exception was raised, then assignment to the scoped variable will occur: as the EL expression in Listing 18 suggests, its value will not be empty.
任何非必需的变量都可以为空。
初始化一个空堆栈，将结果字符串变量置空。
在许多空指针异常中，真正的错误出现在变量被赋为空值的地方。
In many null-pointer exceptions, the true bug occurs where the variable is actually assigned to null.
如果解析后的上下文变量内容为空，则不会发生替换，并且变量名称在查询字符串中保持不变(包括“%”符号)。
If the resolved context variable content is null, no replacement occurs and the variable name remains unchanged in the query string (including the "%" signs).
其他的特性还包括类不变量、非空引用类型和加强的静态分析功能。
Other features include class invariants, non-nullable reference types, and enhanced static analysis capabilities.
否则，该变量仍为空。
如果是前一种情况，那么该列的指示符变量被设置为- 1，这导致该列被更新为空值。
If the former is true, then the indicator variable for that column is set to -1 which results in the column being updated with the null value.
检查下面所需的HADR变量(参见清单3)这些变量必须正确而且不能为空。
Check the required HADR variables below (see Listing 3). They must be correct and cannot be empty.
为什么是静态变量空时，我尝试在另一个类的访问？
Why is the static variable null when I try to access it in another class?
在DB 2fori 6.1发布之前，SQLUpdate和insert语句能够使用一个值为- 1的指示符变量，将支持空值的列设置为空值。
Prior to the DB2 for I 6.1 release, SQL Update and Insert statements could use an indicator variable with a value of -1 to set a null capable column to the null value.
修改这个blankModelPath变量使其指向这个空白的（空的）模型模版（这个文件将不会被改写）。
Modify the blankModelPath argument to point to the blank (empty) model template (this file will not be overridden).
一个值为空列表或由多个空串组成的变量具有否定的逻辑值。
A variable whose value is an empty list or which consists entirely of empty strings has a negative logical value.
当变量为空或者未分配的时候，将由给定的默认值替代输出。
If the variable is empty or unset, the given default value is printed instead. Default takes one argument.
为什么这个变量需要在对象设置设置为空？
Why does this variable need to be set to null after the object is disposed?
如果指定的参数值少于变量的总数，那么伟被赋值的变量将显示空值。
However, if there are less specifiers than variables, the extra variables contain NULL.
或者，引用类型变量可能不存放对任何对象的引用，这种情况称为空引用。
Or a reference type variable might not hold a reference to any object, in which case it is said to be a null reference or a reference to Nothing.
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