在c ++或java中typecasting和typeconversion之间有什么区别？ [英] what is the difference between typecasting and typeconversion in c++ or java?

问题描述

在c ++或java中的typecasting和typeconversion之间有什么区别？

what is the difference between typecasting and typeconversion in c++ or java ?

推荐答案

/ em> 将由变量引用的值（内存块）视为与该变量声明的类型不同的类型。

Type casting is treating a value (block of memory) referenced by a variable as being of a different type than the type the variable is declared as.

在许多语言中， em> casts（通常是数字）会产生转换（这种情况会因语言而有所不同），但大多数情况下只是将此X视为Y。

In many languages, some casts (usually numeric ones) do result in conversions (this will vary quite a bit by language), but mostly it's just "treat this X as a Y".

像人类语言的大多数方面，不幸的是，这些术语在不同的社区中使用略有不同，主要是沿着语言线。例如，见James在下面关于C ++的评论 —词cast有比上述定义更广泛的意义，这在C或Java模型中更多。为了使事情变得有趣，Java语言规范实际上涉及到各种种类的转换，包括 投放转换 。

Like most aspects of human language, unfortunately the terms are used slightly differently in different communities, mostly along language lines. For instance, see James' comment below about C++ — the word "cast" there has a much broader meaning than the above definition, which is more in the C or Java mold. And just to make things fun, the Java Language Spec actually gets into various kinds of casts, including casting conversions. But the above is a good rule of thumb.

在Java中，

在处理地图之前，必须进行很多类型转换：

In Java, prior to generics it wasn't unusual to have to do a lot of typecasting when dealing with maps:

Map m = new HashMap();
m.put("one", "uno");

// This would give a compiler error, because although we know
// we'll get a String back, all the compiler knows is that it's
// an Object
String italian = m.get("one");

// This works, we're telling the compiler "trust me, it's a String"
String italian = (String)m.get("one");

幸运的是，泛型解决了这个问题，因为这样的转换往往是一个具有维护问题的脆弱过程。

Fortunately, the addition of generics addressed this, as casting in this way tends to be a fragile process with maintenance issues.

相反， > convert 如果您有一个数字字符串：

In contrast, you'd convert if you had a String of digits:

String s = "1234";

...需要知道这些数字以十进制表示的数字：

...and needed to know what number those digits represented in decimal:

// Wrong (cast)
int n = (int)s;

// Right (conversion)
int n = Integer.parseInt(s, 10);

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