解决Java中int不能为空而Oracle数据库中Number可以的问题
在应用Hibernate开发中遇到了一个问题:Oracle数据库中某字段(Number类型)没有值(即NULL),其映射的JavaBean对应属性为int类
前言:空(NULL)和零(0)一样吗?当然不。Null表示不存在或不确定,0表示没有。
在应用Hibernate开发中遇到了一个问题:Oracle数据库中某字段(Number类型)没有值(即NULL),其映射的JavaBean对应属性为int类型。在获取数据时,提示“将NULL值赋给基本类型失败”的错误。怎么解决呢?对我这个.NET转Java的新手来说还真有点晕。
1.先来谈谈int和Integer
int永远也不会为空,因为它是primitive数据类型。初始时缺省为0,而不是null。
Integer是对象类,倒可能是null。
因此
int i1;
Integer i2;
此时
i1==0 为true
i2==0 会出错吧
i2==null为true
2.修改int为Integer的解决方案
将配置文件改为:
JavaBean中做以下修改:
public void setA252(Integer a252) {
if(a252 != null){
this.a252 = a252;
}
else{
this.a252 = 0;
}
}
3.JDBC的解决方案
String result = rs.getString(1);
if (result != null){
a252 = Integer.parseInt(result);
}
else{
a252 = 0;
}
4.装箱、拆箱及其他
类型转换是在1.5中才有的。在明白怎么进行判断之前,,我们必须明白所谓的类型转换到底是什么东西。在1.5之前,你如果需要把一个int转换为Integer,你就必须做new Integer(intValue);这样的代码工作。因此在1.5中,Java的缔造者们认为这种方法过于低效率,因此引入了C#中的auto-boxing理念,因此你可以用类型转换的方法创造出一个Integer类实例。但是,其中的原理还是和以前一致的。因为在int类型中,永远不可能有null的取值,因此也不可能生成一个null的Integer对象。
另外可以强制转换下,也就是 (Object)int x == null;

Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

Notepad++7.3.1
Easy-to-use and free code editor

SublimeText3 Chinese version
Chinese version, very easy to use

Zend Studio 13.0.1
Powerful PHP integrated development environment

Dreamweaver CS6
Visual web development tools

SublimeText3 Mac version
God-level code editing software (SublimeText3)

Hot Topics



Full table scanning may be faster in MySQL than using indexes. Specific cases include: 1) the data volume is small; 2) when the query returns a large amount of data; 3) when the index column is not highly selective; 4) when the complex query. By analyzing query plans, optimizing indexes, avoiding over-index and regularly maintaining tables, you can make the best choices in practical applications.

InnoDB's full-text search capabilities are very powerful, which can significantly improve database query efficiency and ability to process large amounts of text data. 1) InnoDB implements full-text search through inverted indexing, supporting basic and advanced search queries. 2) Use MATCH and AGAINST keywords to search, support Boolean mode and phrase search. 3) Optimization methods include using word segmentation technology, periodic rebuilding of indexes and adjusting cache size to improve performance and accuracy.

Yes, MySQL can be installed on Windows 7, and although Microsoft has stopped supporting Windows 7, MySQL is still compatible with it. However, the following points should be noted during the installation process: Download the MySQL installer for Windows. Select the appropriate version of MySQL (community or enterprise). Select the appropriate installation directory and character set during the installation process. Set the root user password and keep it properly. Connect to the database for testing. Note the compatibility and security issues on Windows 7, and it is recommended to upgrade to a supported operating system.

The difference between clustered index and non-clustered index is: 1. Clustered index stores data rows in the index structure, which is suitable for querying by primary key and range. 2. The non-clustered index stores index key values and pointers to data rows, and is suitable for non-primary key column queries.

Article discusses popular MySQL GUI tools like MySQL Workbench and phpMyAdmin, comparing their features and suitability for beginners and advanced users.[159 characters]

Article discusses strategies for handling large datasets in MySQL, including partitioning, sharding, indexing, and query optimization.

MySQL is an open source relational database management system. 1) Create database and tables: Use the CREATEDATABASE and CREATETABLE commands. 2) Basic operations: INSERT, UPDATE, DELETE and SELECT. 3) Advanced operations: JOIN, subquery and transaction processing. 4) Debugging skills: Check syntax, data type and permissions. 5) Optimization suggestions: Use indexes, avoid SELECT* and use transactions.

In MySQL database, the relationship between the user and the database is defined by permissions and tables. The user has a username and password to access the database. Permissions are granted through the GRANT command, while the table is created by the CREATE TABLE command. To establish a relationship between a user and a database, you need to create a database, create a user, and then grant permissions.
