blocks|key|1442408|text|AFAIK，在java中没有办法定义整数的大小。在这里，它始终是32位int作为提到过。但是一些编程语言可能允许指定整数的大小(Ex:+Ada)。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1442409|当编译器试图将代码转换为machine+code+instructions时，会出现性能问题(请参阅这里和这里)。通常，机器代码指令是32位或64位。如果我们的into与机器代码中的大小相同，那么很容易将它们转换为机器代码。否则，编译器需要付出额外的努力将它们转换为机器代码。这就是性能问题出现的时候。|style|CODE|1442410|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/15004944/max-value-of-integer|1|http://en.wikibooks.org/wiki/A-level_Computing/AQA/Computer_Components,_The_Stored_Program_Concept_and_the_Internet/Machine_Level_Architecture/Machine_code_and_processor_instruction_set|2|http://en.wikipedia.org/wiki/Machine_code^0|14|3|0|0|C|P|1E|2|1|1H|2|2|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@$A|U|B|V|1|W]]|C|$]]|$1|D|3|E|5|6|7|X|8|@$A|Y|B|Z|F|G]]|9|@$A|10|B|11|1|12]|$A|13|B|14|1|15]]|C|$]]|$1|H|3|-4|5|6|7|16|8|@]|9|@]|C|$]]]|I|$J|$5|K|L|M|C|$N|O]]|P|$5|K|L|M|C|$N|Q]]|R|$5|K|L|M|C|$N|S]]]]

AFAIK, there is no way in java to define the size of an integer. It is always an 32 bit int as <a href="https://stackoverflow.com/questions/15004944/max-value-of-integer">mentioned</a> here. But some programming languages may allow to specify the size of the integer (Ex: Ada).

The performance issue comes when compiler try to convert our code to <code>machine code instructions</code> (See <a href="http://en.wikibooks.org/wiki/A-level_Computing/AQA/Computer_Components,_The_Stored_Program_Concept_and_the_Internet/Machine_Level_Architecture/Machine_code_and_processor_instruction_set" rel="nofollow noreferrer">here</a> and <a href="http://en.wikipedia.org/wiki/Machine_code" rel="nofollow noreferrer">here</a>). Normally machine code instructions are 32 or 64 bits. If our ints are same as the size in machine code, it is easy to convert them into the machine code. Otherwise compiler needs to put an extra effort to covert them into the machine code. That's when the performance issue comes.

blocks|key|1442532|text|在“低级”语言中，原始数据类型大小通常来自CPU处理它们的能力。例如，在C中，int被定义为“至少16位大小”，但其大小在不同的体系结构中可能有所不同，以确保“int类型应该是目标处理器最有效处理的整数类型。”(来源)。这意味着，如果您的代码对int的大小做了粗心的假设，如果您将其从32位x86移植到64位powerpc，它很可能会中断。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1442533|如上所述，java是不同的。例如，一个int总是32位。这意味着，当您在不同的架构上运行相同的代码时，您不必担心它的大小会发生变化。正如上面所提到的，代价是性能--在任何本机不处理32位计算的体系结构上，这些int需要扩展到CPU可以处理的本机大小(这将带来很小的损失)，或者更糟的是，如果CPU只能处理较小的int，那么int上的每个操作可能需要几个CPU操作。|1442534|entityMap|0|LINK|mutability|MUTABLE|url|/questions/tagged/c|1|https://en.wikipedia.org/wiki/C_data_types#Basic_types|2|/questions/tagged/x86|3|/questions/tagged/powerpc|4|/questions/tagged/java^0|13|3|3E|3|10|1|0|2Y|2|1|41|3|2|4A|7|3|0|J|3|2W|3|4B|3|4H|3|5|4|4|0^^$0|@$1|2|3|4|5|6|7|X|8|@$9|Y|A|Z|B|C]|$9|10|A|11|B|C]]|D|@$9|12|A|13|1|14]|$9|15|A|16|1|17]|$9|18|A|19|1|1A]|$9|1B|A|1C|1|1D]]|E|$]]|$1|F|3|G|5|6|7|1E|8|@$9|1F|A|1G|B|C]|$9|1H|A|1I|B|C]|$9|1J|A|1K|B|C]|$9|1L|A|1M|B|C]]|D|@$9|1N|A|1O|1|1P]]|E|$]]|$1|H|3|-4|5|6|7|1Q|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]|P|$5|K|L|M|E|$N|Q]]|R|$5|K|L|M|E|$N|S]]|T|$5|K|L|M|E|$N|U]]|V|$5|K|L|M|E|$N|W]]]]

In "lower" languages, primitive data types sizes are often derived from the CPU's ability to handle them.
E.g., in <a href="/questions/tagged/c" class="post-tag" title="show questions tagged &#39;c&#39;" rel="tag">c</a>, an <code>int</code> is defined as being "at least 16 bits in size", but its size may vary between architectures in order to assure that "The type int should be the integer type that the target processor is most efficient working with." (<a href="https://en.wikipedia.org/wiki/C_data_types#Basic_types" rel="nofollow noreferrer">source</a>). This means that if your code makes careless assumptions about an <code>int</code>'s size, it may very well break if you port it from 32-bit <a href="/questions/tagged/x86" class="post-tag" title="show questions tagged &#39;x86&#39;" rel="tag">x86</a> to 64-bit <a href="/questions/tagged/powerpc" class="post-tag" title="show questions tagged &#39;powerpc&#39;" rel="tag">powerpc</a>.

<a href="/questions/tagged/java" class="post-tag" title="show questions tagged &#39;java&#39;" rel="tag">java</a>, as noted above, is different. An <code>int</code>, e.g., will always be 32 bits. This means you don't have to worry about its size changing when you run the same code on a different architecture. The tradeoff, as also mentioned above, is performance - on any architecture that doesn't natively handle 32 bit calculations, these <code>int</code>s need to be expanded to the native size the CPU can handle (which will have a small penalty), or worse, if the CPU can only handle smaller <code>int</code>s, every operation on an <code>int</code> may require several CPU operations.

blocks|key|1442569|text|Java在底层系统指针机制的顶部实现了自己的数据指针机制。如果数据不够大，许多系统可能会使用较小的指针。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1442570|For+ex:如果您的整数数据只需要16位指针，系统将只分配使用16位指针的所需存储空间。但是如果您使用Java，它将把16位转换为32位指针分配，其中需要大内存空间，这也降低了存储和数据查找的性能。因为您的指针是大。|offset|length|style|BOLD|1442571|entityMap^0|0|0|7|2H|2|2K|4|2Z|1|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@$D|L|E|M|F|G]|$D|N|E|O|F|G]|$D|P|E|Q|F|G]|$D|R|E|S|F|G]]|9|@]|A|$]]|$1|H|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|I|$]]

Java implements its own data pointer mechanism on the top of the underlying system' pointer mechanism. Lot of the systems may use smaller pointers if the data is not large enough. 

For ex: If your integer data only requires 16 bit pointer, system will only allocate required storage where 16 bit pointer is used. But if you are using Java, it will convert 16 bit into 32 bit pointer allocation where large memory space is required which also degrades performance in terms of storage and data seek. Because your pointer is large.

blocks|key|1442612|text|一些(非常少的)+计算机使用36位结构。，所以您需要额外的一步来屏蔽比特，模拟溢出，等等。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1442613|entityMap|0|LINK|mutability|MUTABLE|url|http://en.m.wikipedia.org/wiki/36-bit^0|9|B|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

A few (very few) <a href="http://en.m.wikipedia.org/wiki/36-bit" rel="nofollow">computers use 36 bit architecture</a>, so you need an extra step to mask off bits, simulate overflows, etc.

I quote from Herbert Schildt Chapter 3 Data types, Variables and Arrays :

<blockquote>
 The primitive types represent single values not complex objects.
 Although Java is otherwise completely object-oriented, the primitive
 types are not. The reason for this efficiency. Making the primitive
 types would have degraded performance too much.
 
 The primitive types are defined to have an explicit range and
 mathematical behavior. Languages such as C, C++ allow the size of an
 integer to vary based upon the dictates of the execution environment.
 However, Java is different. Because of Java’s portability requirement,
 all data types have a strongly defined range. For example, an int is
 always 32-bit regardless of the particular platform. This allows
 programs to be written that are guaranteed to run without porting on
 any machine architecture. While strictly specifying the size of an
 integer may cause a small loss of performance in some environments, it
 is necessary in order to achieve portability.
</blockquote>

What does he mean by the last 2 lines ? And how come specifying the size of an integer may cause a small loss of performance in some environments?

Primitive data types and portability in Java

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

文章

问答

视频

教程

学习中心

腾讯云实验室

直播

竞赛

腾讯云代码分析专区

腾讯iOA零信任安全管理系统专区

腾讯云架构师技术同盟交流圈

腾讯云数据库专区

腾讯云智能顾问专区

腾讯云原生专区

腾讯混元专区

腾讯云TCE专区

腾讯云Lighthouse专区

腾讯云HAI专区

腾讯云Edgeone专区

腾讯云存储专区

腾讯云智能专区

腾讯轻联专区 

腾讯云开发专区

TAPD专区

腾讯轻量云游戏服专区

腾讯云最具价值专家

腾讯云架构师技术同盟

腾讯云创作之星

腾讯云开发者先锋

腾讯云代码助手

云原生构建

TAPD 敏捷项目管理

Cloud Studio

SDK中心

API中心

命令行工具

涵盖代码开发、场景应用、自动测试全流程，助你从零构建专属AI助手

一站式MCP教程库，解锁AI应用新玩法

聚焦“写作效率、视觉美观与运行性能”三方面进行全面升级，为您提供更高效、稳定的创作环境

社区富文本&Markdown编辑器全新改版上线，欢迎大家体验!

诚挚邀请您参与本次调研，分享您的真实使用感受与建议。您的反馈至关重要，感谢您的支持与参与！

社区新版编辑器体验调研

我引用Herbert Schildt第3章的数据类型、变量和数组：基元类型表示单个值，而不是复杂对象。虽然Java在其他方面是完全面向对象的，但原语类型却不是。这种效率的原因。制造原始类型会大大降低性能。原语类型被定义为具有显式范围和数学行为。C、C++等语言允许整数的大小根据执行环境的要求而变化。然而，Java是不同...

问Java中的原始数据类型与可移植性
EN

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问Java中的原始数据类型与可移植性EN