blocks|key|1151215|text|下面是两种语言的一个非常全面的比较：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1151216|http://www.25hoursaday.com/CsharpVsJava.html|offset|length|1151217|新增：http://en.wikipedia.org/wiki/Comparison_of_Java_and_C_Sharp|1151218|entityMap|0|LINK|mutability|MUTABLE|url|1|http://en.wikipedia.org/wiki/Comparison_of_Java_and_C_Sharp^0|0|0|18|0|0|3|1N|1|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@]|9|@$D|S|E|T|1|U]]|A|$]]|$1|F|3|G|5|6|7|V|8|@]|9|@$D|W|E|X|1|Y]]|A|$]]|$1|H|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|I|$J|$5|K|L|M|A|$N|C]]|O|$5|K|L|M|A|$N|P]]]]

here is a very comprehensive comparison of the 2 languages:

<a href="http://www.25hoursaday.com/CsharpVsJava.html" rel="noreferrer">http://www.25hoursaday.com/CsharpVsJava.html</a>

Added: <a href="http://en.wikipedia.org/wiki/Comparison_of_Java_and_C_Sharp" rel="noreferrer">http://en.wikipedia.org/wiki/Comparison_of_Java_and_C_Sharp</a>

blocks|key|1366833|text|令我惊讶的是，没有人提到属性，这是C#中非常基本的东西，但在Java语言中却没有。C#+3和更高版本也自动实现了属性。在Java中，您必须使用GetX/SetX类型方法。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1366834|另一个明显的区别是Java3中没有LINQ和lambda表达式。|1366835|Java中还缺少其他一些简单但有用的东西，如逐字字符串(@"")、运算符重载、使用yield的迭代器和预处理器。|1366836|在C#中，我个人最喜欢的一点是名称空间名称不必遵循物理目录结构。我真的很喜欢这种灵活性。|1366837|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|L|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|M|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

I am surprised that no one has mentioned properties, something quite fundamental in C# but absent in Java. C# 3 and above has automatically implemented properties as well. In Java you have to use GetX/SetX type methods.

Another obvious difference is LINQ and lambda expressions in C# 3 absent in Java.

There are a few other simple but useful things missing from Java like verbatim strings (@""), operator overloading, iterators using yield and pre processor are missing in Java as well.

One of my personal favourites in C# is that namespace names don't have to follow the physical directory structure. I really like this flexibility.

blocks|key|1151520|text|.NET具体化了泛型；Java擦除了泛型。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1151521|不同之处在于:如果您有一个ArrayList<String>对象，在.NET中，您可以(在运行时)知道该对象的类型为ArrayList<String>，而在Java语言中，在运行时，该对象的类型为ArrayList；String部分会丢失。如果您将非String对象放入ArrayList中，系统将无法强制执行此操作，并且您只有在尝试提取该项之后才会知道这一点，并且强制转换失败。|offset|length|style|CODE|1151522|entityMap^0|0|D|H|1M|H|2Q|9|30|6|3H|6|3R|9|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]|$D|R|E|S|F|G]|$D|T|E|U|F|G]|$D|V|E|W|F|G]]|9|@]|A|$]]|$1|H|3|-4|5|6|7|X|8|@]|9|@]|A|$]]]|I|$]]

.NET has reified generics; Java has erased generics.

The difference is this: if you have an <code>ArrayList&lt;String&gt;</code> object, in .NET, you can tell (at runtime) that the object has type <code>ArrayList&lt;String&gt;</code>, whereas in Java, at runtime, the object is of type <code>ArrayList</code>; the <code>String</code> part is lost. If you put in non-<code>String</code> objects into the <code>ArrayList</code>, the system can't enforce that, and you'll only know about it after you try to extract the item out, and the cast fails.

blocks|key|1366670|text|在Java的C#中，我遗漏的一件事是强制处理检查异常。在C#中，人们不知道方法可能抛出的异常是很常见的，而您只能任由文档或测试来发现它们。在带有检查异常的Java中则不是这样。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1366671|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

One thing I miss in C# from Java is the forced handling of checked exceptions. In C# is it far to common that one is unaware of the exceptions a method may throw and you're at the mercy of the documentation or testing to discover them. Not so in Java with checked exceptions.

blocks|key|1151643|text|Java为原语而不是值类型提供了自动装箱功能，因此尽管System.Int32[]是C#中的值数组，但Integer[]是对Integer对象的引用数组，因此不适合进行更高性能的计算。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1151644|entityMap^0|R|E|1F|9|1Q|7|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|O|8|@]|D|@]|E|$]]]|G|$]]

Java has autoboxing for primitives rather than value types, so although <code>System.Int32[]</code> is an array of values in C#, <code>Integer[]</code> is an array of references to <code>Integer</code> objects, and as such not suitable for higher performance calculations.

blocks|key|1151290|text|没有委托或事件--你必须使用接口。幸运的是，您可以内联创建类和接口实现，所以这不是什么大问题|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1151291|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

No delegates or events - you have to use interfaces. Fortunately, you can create classes and interface implementations inline, so this isn't such a big deal

blocks|key|1151367|text|Java中没有委托。因此，除了委派给谈判桌带来的所有好处外，事件的工作方式也不同。您需要实现一个接口并附加该接口，而不是仅仅连接一个方法。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1151368|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

There are no delegates in Java. Therefore, aside from all the benefits that delegates bring to the table, events work differently too. Instead of just hooking up a method, you need to implement an interface and attach that instead.

blocks|key|1366551|text|在我的面试清单中，有一件事让我很吃惊，那就是Java中没有类似于方法隐藏的"+new“关键字，因此也没有编译器警告”你应该把new放在这里“。当你打算重写时，意外的方法隐藏会导致错误。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1366552|(例如编辑)例如，B派生自A(使用Java语法，C#的行为与我上次检查时的行为相同，但不发出编译器警告)。A的foo会被调用，还是B的foo会被调用？(A的被调用，可能会让实现B的开发人员大吃一惊)。|1366553|class+A+
{
public+void+foo()+{code}
}

class+B:A
{
public+void+foo()+{code}
}++++

void+SomeMethod()
{
A+a+=+new+B();+//+variable's+type+is+declared+as+A,+but+assigned+to+an+object+of+B.
a.foo();
}|code-block|syntax|javascript|1366554|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

One thing that jumps out b/c it's on my interview list is that there is no "new" keyword analogue in Java for method hiding and there fore no compiler warning "you should put new here". Accidental method hiding when you meant to override leads to bugs.

(edit for example)
Example, B derives from A (using C# syntax, Java behaves same way last I checked but does not emit compiler warning). Does A's foo get called, or B's foo? (A's gets called, probably surprising the dev who implemented B).

<pre><code>class A 
{
public void foo() {code}
}

class B:A
{
public void foo() {code}
} 

void SomeMethod()
{
A a = new B(); // variable's type is declared as A, but assigned to an object of B.
a.foo();
}
</code></pre>

blocks|key|1366961|text|Java没有LINQ，文档简直是地狱。Java中的用户界面开发起来很痛苦，你会失去微软给我们的所有好处(WPF、WCF等)。但是得到难以使用的、几乎没有文档记录的“API”。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1366962|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Java doesn't have LINQ and the documentation is hell. User interfaces in Java are a pain to develop, you lose all the good things Microsoft gave us (WPF, WCF, etc...) but get hard - to - use, hardly documented "APIs".

blocks|key|1151587|text|到目前为止，我在使用来自C#的Java时遇到的一个问题是异常和错误是不同的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1151588|例如，您不能使用catch捕获内存不足错误(异常e)。|1151589|有关更多详细信息，请参阅以下内容：|1151590|why-is-java-lang-outofmemoryerror-java-heap-space-not-caught|offset|length|1151591|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/1888602/why-is-java-lang-outofmemoryerror-java-heap-space-not-caught^0|0|0|0|0|1O|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|S|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|T|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|U|8|@]|9|@$H|V|I|W|1|X]]|A|$]]|$1|J|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|K|$L|$5|M|N|O|A|$P|Q]]]]

The one issue I've run into so far when working with Java coming from C# is Exceptions and Errors are different.

For example you cannot catch an out of memory error using catch(Exception e).

See the following for more details:

<a href="https://stackoverflow.com/questions/1888602/why-is-java-lang-outofmemoryerror-java-heap-space-not-caught">why-is-java-lang-outofmemoryerror-java-heap-space-not-caught</a>

blocks|key|1151682|text|我已经很久没有使用Java语言了，但我在应用程序开发中立刻注意到的事情是C#事件模型、C#拖放和使用Swing中的布局管理器(如果您正在进行应用程序开发)，以及使用Java语言进行异常处理，以确保捕获异常而不需要C#。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1151683|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

It's been so long since I've been in Java but the things I noticed right off the bat in application development was C# event model, C# drag and drop vs using Layout Managers in Swing (if your doing App dev), and exception handling with Java making sure you catch an exception and C# not required.

blocks|key|1366878|text|当我切换到java时，对我来说最大的区别是字符串声明。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1366879|在Java+String中的C#+string+(大多数情况下)|offset|length|style|CODE|1366880|这很简单，但相信我，当你习惯于s而不是S时，它会让你浪费很多时间！|1366881|entityMap^0|0|6|6|H|6|0|F|1|J|1|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@$D|N|E|O|F|G]|$D|P|E|Q|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|R|8|@$D|S|E|T|F|G]|$D|U|E|V|F|G]]|9|@]|A|$]]|$1|J|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|K|$]]

The most harrasing difference to me when I switch to java it's the string declaration.

in C# <code>string</code> (most of the time)
in Java <code>String</code>

It's pretty simple, but trust me, it makes you lose so much time when you have the habit to <code>s</code> not <code>S</code> !

blocks|key|1151887|text|在回答你在标题中非常直接的问题时：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1151888|“学习Java的C#开发人员，最大的区别是什么？”|1151889|答:+Java在Windows上的速度要慢得多。|1151890|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

In response to your very direct question in your title:

"C# developers learning Java, what are the biggest differences one may overlook?"

A: The fact that Java is considerably slower on Windows.

For c# developers that are staring out to learn Java, are there any big underlying differences between the two languages that should be pointed out?

Maybe some people may assume things to be the same, but there are some import aspects that shouldn't be overlooked? (or you can really screw up!)

Maybe in terms of OOP constructs, the way GC works, references, deployment related, etc.

C# developers learning Java, what are the biggest differences one may overlook?

编译器

Windows

Java

对于开始学习Java的c#开发人员来说，这两种语言之间有什么值得指出的重大潜在差异吗？也许有些人会认为事情是一样的，但是有一些重要的方面是不应该被忽视的？(或者你可能真的搞砸了！)也许在OOP结构、GC的工作方式、引用、部署等方面。

问学习C#的开发人员，人们可能忽略的最大区别是什么？
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