blocks|key|2546318|text|它的运行时|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2546319|Foo+f指的是Object在运行时创建的Bar运行时。|offset|length|style|CODE|2546320|有编译时检查它。要成功编译，Bar必须是Foo。|2546321|entityMap^0|0|0|5|8|6|L|3|0|E|3|K|3|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]|$D|P|E|Q|F|G]|$D|R|E|S|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|T|8|@$D|U|E|V|F|G]|$D|W|E|X|F|G]]|9|@]|A|$]]|$1|J|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|K|$]]

Its runtime

<code>Foo f</code> would be referring to <code>Object</code> created runtime of <code>Bar</code> at runtime.

There are compile time check for it. <code>Bar</code> must be a <code>Foo</code> for this to compile successfully

blocks|key|406367|text|如果您编译了以下内容：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|406368|int+x+=+34+%2B+45;|code-block|syntax|javascript|406369|然后，您分配的表达式将在编译时进行计算，因为它只涉及常量基本类型。在大多数其他情况下，包括您的示例，表达式将在运行时进行计算。|406370|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

If you compile the following:

<pre><code>int x = 34 + 45;
</code></pre>

then the expression that you are assigning will be evaluated at compile time because it involves only constant basic types. In most other cases, including your example, the expression will be evaluated at runtime.

blocks|key|2546382|text|我不知道您到底怀疑什么，但我认为在编译过程中，程序的文本表示被转换成机器可理解的形式(在Java情况下，它将是Java字节代码)。类似于分配之类的操作也会发生同样的情况。在运行时，这样的操作被执行。因此，要准确地回答您的问题，赋值操作是编译和运行时现象(在这两种情况下都会执行某些操作--在编译的情况下，它们是由Java编译器完成的，而在运行时则是由JVM完成的)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2546383|例如,|2546384|class+Foo+{+}
class+Bar+{+}
Foo+f+=+new+Bar();|code-block|syntax|javascript|2546385|此代码将被编译器拒绝。它会对您大喊大叫，因为您正在尝试分配不兼容的类型。|2546386|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|O|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

I don't know what exactly is your doubt, but I think that during compilation textual representation of a program is translated into machine-understandable form (in Java case it'd be Java byte code). The same happens with operations like assignments. In runtime, such operations are executed. So to precisely answer your question, the assignment operation is both compile and runtime phenomenon (certain actions are taken in both cases - in a case of compilation they're done by Java compiler and in runtime the're done by JVM).

For instance,

<pre><code>class Foo { }
class Bar { }
Foo f = new Bar();
</code></pre>

This code will be rejected by compiler. It will yell at you that you are trying to assign incompatible types.

blocks|key|427004|text|两者都有。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|427005|在编译时分析赋值以实现类型兼容性，为执行转换/装箱/取消装箱等工作注入代码。即使是一些流分析也会影响赋值，例如变量及其分配可以在completely.|427006|Run时间之外进行优化--一个值的实际赋值，即在运行时更改变量内存位置中的位。|unordered-list-item|427007|427008|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|L|8|@]|9|@]|A|$]]|$1|G|3|-4|5|6|7|M|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

Its both.

<ol>
<li>Compile time - an assignment is analyzed at compile time for type compatibility, for the injection of code to do conversion/boxing/unboxing, etc. Even some flow analysis can affect an assignment, e.g. variable and its assignment can be optimized away completely.</li>
<li>Run time - the actual assignment of a value, i.e. changing the bits in the variable's memory location, of course, happens at run-time.</li>
</ol>

I had a doubt, 

<blockquote>
 Any expression assignment operation is
 a compile time or runtime phenomenon ? 
 <code>e.g Foo f=new Bar();</code>
</blockquote>

Thanks.

Assignment of expression - Compile or Runtime phenomenon

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。

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我有个疑问任何表达式赋值操作都是编译时或运行时的现象？e.g Foo f=new Bar();谢谢。

问表达式分配-编译或运行时现象
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