null

简明释义

英[nʌl]美[nʌl]

adj. 无约束力的，无效的；零值的，等于零的；（数）（集合，矩阵）空的，元素只有零的；无特征的，无内涵的

n. <文>零；（密码中的）无意义暗码；（电子）无信号；无电磁辐射的方向

v. 使（信号）与另一信号结合产生无信号状态，抵消

英英释义

单词用法

同义词

反义词

例句

1.If nullable, it will contain the null value.

如果可为空，它将包含null值。

2.Null pointers everywhere!

空指针到处都有！

3.A spokeswoman said the agreement had been declared null and void.

一位女发言人说那个协议已被宣布为无效的。

4.The breakup of the null can be ruled out as the cause of the sinking.

空值的分解可以排除为下沉的原因。

5.Therefore, it is null.

因此，它是空的。

6.Null-pointer exceptions will never be completely eradicated.

空指针异常将决不会被完全根除。

7.NOT NULL - a NULL was found in field name.

NOTNULL——字段名中出现空值。

8.SQL2032 is returned if null.

如果为空，则返回SQL2032。

9.That vector is called a "null vector".

那种矢量就叫做”零矢量“。

10.The variable was set to null to indicate that it has no value.

该变量被设置为空，表示它没有值。

11.If the input is null, the function will return an error.

如果输入是空，函数将返回一个错误。

12.In database terms, a null entry means that the data is missing.

在数据库术语中，空条目意味着数据缺失。

13.The user profile cannot be created because the username is null.

无法创建用户个人资料，因为用户名是空的。

14.You must not pass a null reference to this function.

您不能向此函数传递空引用。

作文

In the realm of computer science and programming, the term null plays a crucial role in understanding how data is managed and utilized. Essentially, null represents the absence of a value or a non-existent reference. It is a concept that can be found in various programming languages, including Java, C++, and Python. The ability to recognize and handle null values is vital for developers as it helps prevent errors and enhances the robustness of applications. When we declare a variable in programming, we often assign it a specific value. However, there are instances when we might not have a value to assign, or we want to indicate that a variable is intentionally left empty. This is where null comes into play. For example, in a database, if a user has not provided information for a particular field, that field may be set to null. This indicates that the value is unknown or does not exist. Understanding how to work with null is essential for error handling. If a programmer tries to access a property or method of an object that is null, it can lead to exceptions or crashes in the program. Thus, many programming languages provide mechanisms to check for null values before performing operations. This practice is crucial for maintaining the integrity of software applications. Moreover, null is often used in conditional statements. For instance, in an if-statement, a developer might check if a variable is null before proceeding with further logic. This ensures that the program behaves as expected and avoids running into unexpected situations that could disrupt its flow. The concept of null is not limited to programming alone; it also extends to databases and data structures. In relational databases, null values are used to represent missing or undefined data. This allows for more flexible data management and querying. For example, when performing SQL queries, one must consider null values to ensure accurate results. A common mistake is to overlook null when filtering data, which can lead to incomplete or misleading outputs. Furthermore, the use of null can vary across different programming languages. Some languages treat null as a distinct type, while others may have multiple representations for 'no value' such as undefined or None. Understanding these differences is important for developers who work with multiple languages, as it can affect how they write code and manage data. In conclusion, the term null encapsulates a fundamental concept in programming and data management. It signifies the absence of a value, which can have significant implications for how software operates. By mastering the use of null, developers can create more reliable and efficient applications. Additionally, recognizing the importance of null in databases and data structures allows for better data handling practices. As technology continues to evolve, the understanding of null will remain a cornerstone of effective programming and data analysis.

在计算机科学和编程领域，术语null在理解数据如何管理和利用方面发挥着至关重要的作用。本质上，null表示值的缺失或不存在的引用。这个概念可以在多种编程语言中找到，包括Java、C++和Python。识别和处理null值的能力对于开发人员至关重要，因为它有助于防止错误并增强应用程序的健壮性。 当我们在编程中声明一个变量时，我们通常会给它赋一个特定的值。然而，有时我们可能没有可分配的值，或者我们想表明一个变量被故意留空。这就是null发挥作用的地方。例如，在数据库中，如果用户没有提供特定字段的信息，该字段可能被设置为null。这表明该值是未知的或不存在。 理解如何处理null对于错误处理至关重要。如果程序员尝试访问一个值为null的对象的属性或方法，可能会导致程序中的异常或崩溃。因此，许多编程语言提供机制来检查null值，以便在执行操作之前进行验证。这种做法对于维护软件应用程序的完整性至关重要。 此外，null通常用于条件语句中。例如，在if语句中，开发人员可能会检查一个变量是否为null，然后再继续进行进一步的逻辑。这确保了程序按预期运行，并避免进入可能破坏其流程的意外情况。 null的概念不仅限于编程；它还扩展到数据库和数据结构。在关系数据库中，null值用于表示缺失或未定义的数据。这允许更灵活的数据管理和查询。例如，在执行SQL查询时，必须考虑null值以确保结果的准确性。一个常见的错误是忽视null值进行数据过滤，这可能导致输出不完整或误导。 此外，null的使用在不同的编程语言中可能有所不同。一些语言将null视为一种独特的类型，而其他语言可能有多种表示“无值”的方式，例如undefined或None。理解这些差异对于使用多种语言的开发人员很重要，因为这会影响他们编写代码和管理数据的方式。 总之，术语null概括了编程和数据管理中的一个基本概念。它表示值的缺失，这对软件的操作方式可能产生重大影响。通过掌握null的使用，开发人员可以创建更可靠和高效的应用程序。此外，认识到null在数据库和数据结构中的重要性，可以促进更好的数据处理实践。随着技术的不断发展，对null的理解将始终是有效编程和数据分析的基石。