blocks|key|2316178|text|最后的字段阻止您更改字段本身(通过将其“指向”到其他实例)，但是如果字段是对可变对象的引用，则没有什么可以阻止您这样做：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2316179|public+void+someFunction+(final+Person+p)+{
++++p+=+new+Person("mickey","mouse");+//cant+do+this+-+its+final
++++p.setFirstName("donald");
++++p.setLastName("duck");
}|code-block|syntax|javascript|2316180|上面的参考p是不变的，但是引用所指向的实际人员是可变的。当然，您可以使类人成为一个不可变的类，如下所示：|2316181|public+class+Person+{
++++private+final+String+firstName;
++++private+final+String+lastName;
++++public+Person(String+firstName,+String+lastName)+{
++++++++this.firstName+=+firstName;
++++++++this.lastName+=+lastName;
++++}
++++//getters+and+other+methods+here
}|2316182|此类类一旦创建，就不能以任何方式进行修改。|2316183|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

final fields prevent you from changing the field itself (by making it "point" to some other instance), but if the field is a reference to a mutable object, nothing will stop you from doing this:

<pre><code>public void someFunction (final Person p) {
 p = new Person("mickey","mouse"); //cant do this - its final
 p.setFirstName("donald");
 p.setLastName("duck");
}
</code></pre>

the reference p above is immutable, but the actual Person pointed to by the reference is mutable.
you can, of course, make class Person an immutable class, like so:

<pre><code>public class Person {
 private final String firstName;
 private final String lastName;
 public Person(String firstName, String lastName) {
 this.firstName = firstName;
 this.lastName = lastName;
 }
 //getters and other methods here
}
</code></pre>

such classes once created, cannot be modified in any way.

blocks|key|2316197|text|这句话只说了这句话：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2316198|使所有字段成为最终字段，除非它们是可变的。|blockquote|2316199|可变字段是以后可以更改为指向另一个对象的字段。如果字段是final，它仍然可以引用可变对象(例如，java.util.Date)。因此，字段是不可变的(总是指向同一个对象)，但这个对象是可变的。|offset|length|style|CODE|2316200|entityMap^0|0|0|S|5|1D|E|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$]]|$1|E|3|F|5|6|7|O|8|@$G|P|H|Q|I|J]|$G|R|H|S|I|J]]|9|@]|A|$]]|$1|K|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|L|$]]

This quote says only what is says:

<blockquote>
 make all fields final unless they need to be mutable
</blockquote>

mutable field is a field that you can later change to point to another object. If the field is <code>final</code>, it can still reference mutable object (e.g. <code>java.util.Date</code>). Thus the field is immutable (always points to the same object), but this object is mutable.

blocks|key|2316213|text|根据Java代码约定，最终变量被视为常量，并在所有Caps中写入。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2316214|private+final+int+COUNT=10;+//+immutable+->+cannot+be+changed|code-block|syntax|javascript|2316215|使集合引用变量最终确定意味着只能更改引用，但可以在集合中添加、删除或更改对象。例如：|2316216|private+final+List+Loans+=+new+ArrayList();
list.add(“home+loan”);++//valid
list.add("personal+loan");+//valid
loans+=+new+Vector();++//not+valid|2316217|阅读更多：http://javarevisited.blogspot.com/2011/12/final-variable-method-class-java.html#ixzz2KP5juxm0|offset|length|2316218|回答你的问题:是的，如果你使用正确的话。|2316219|entityMap|0|LINK|mutability|MUTABLE|url|http://javarevisited.blogspot.com/2011/12/final-variable-method-class-java.html#ixzz2KP5juxm0^0|0|0|0|0|5|2L|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|10|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|12|8|@]|9|@$M|13|N|14|1|15]]|A|$]]|$1|O|3|P|5|6|7|16|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|17|8|@]|9|@]|A|$]]]|R|$S|$5|T|U|V|A|$W|X]]]]

As per Java code convention final variables are treated as constant and written in all Caps e.g.

<pre><code>private final int COUNT=10; // immutable -&gt; cannot be changed
</code></pre>

Making a collection reference variable final means only reference can not be changed but you can add, remove or change object inside collection. For example:

<pre><code>private final List Loans = new ArrayList();
list.add(“home loan”); //valid
list.add("personal loan"); //valid
loans = new Vector(); //not valid
</code></pre>

Read more: <a href="http://javarevisited.blogspot.com/2011/12/final-variable-method-class-java.html#ixzz2KP5juxm0" rel="nofollow">http://javarevisited.blogspot.com/2011/12/final-variable-method-class-java.html#ixzz2KP5juxm0</a>

To answer your question: Yes, if you use them correctly.

blocks|key|1525504|text|在java中，类似于以下内容：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1525505|int+*const+p=&something+++//constant+pointer.in+c%2B%2B.+you+can't+use+this+pointer+to+change+something+but+that+something+can+be+changed+with+its+own.|offset|length|style|CODE|1525506|在java中，最后的字段不能被更改，但是它们所引用的对象可能会因其自身而改变。例如。'this'是最终的，您不能将任何东西分配给this，但是您可以将任何东西分配给它所引用的对象。|1525507|从你的问题：|1525508|it+is+a+good+practice+to+make+all+fields+final+unless+they+need+to+be+mutable.|1525509|为了避免对原作的任何修改(无论是逻辑上的还是偶然的)，让它们成为最终的总是好的。|1525510|entityMap^0|0|0|43|0|16|6|1S|4|0|0|0|26|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|S|8|@$D|T|E|U|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|V|8|@$D|W|E|X|F|G]|$D|Y|E|Z|F|G]]|9|@]|A|$]]|$1|J|3|K|5|6|7|10|8|@]|9|@]|A|$]]|$1|L|3|M|5|6|7|11|8|@$D|12|E|13|F|G]]|9|@]|A|$]]|$1|N|3|O|5|6|7|14|8|@]|9|@]|A|$]]|$1|P|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|Q|$]]

in java final is similer to this:

<code>int *const p=&amp;something //constant pointer.in c++. you can't use this pointer to change something but that something can be changed with its own.</code>

in java final fields can't be changed but the object to who they refer may change by its own .
Ex. <code>'this'</code> is final you can't assign anything to <code>this</code> but you can assign to object to whom this refer.

From your Ques:

<code>it is a good practice to make all fields final unless they need to be mutable.</code>

to just avoid any modification(either logically or accidently) to original it's always good to make them final.

blocks|key|1525553|text|别管这句话了。时不时地让你的代码与final擦亮几乎没有什么好处。作者的目标是一个好的实践，但在大规模的代码库中，看到一切都变得模糊了意图，使得阅读代码变得更加困难和模糊--而且可能没有什么好处。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1525554|两种方法|1525555|不过，一般有两所学校。选择你的：|1525556|反对，除非真的需要|ordered-list-item|1525557|一种是不使用final，除非您真的希望那些阅读您编写的代码的人知道这个字段在某种程度上是特殊的，是不可小觑的。|1525558|因为，从来没有一个不好的地方可以使用决赛！|1525559|另一种是对final的迷恋，并希望它无处不在。不太普遍。雷纳尔德·瓦杜拉是这一思想的优秀传播者。阅读他的链接条目，标题为"Final+on+final关键字“，这是一个很好和深入的阅读。|BOLD|1525560|可能依赖于您使用的Java|1525561|就我而言，我只想让您知道final发生了变化，并不总是意味着不可更改，因为您可以在Heinz+Kabutz‘Java专业通讯中阅读。他向您介绍了它在不同Javas中的工作方式，您可以随意使用他的代码并检查您使用的Java。|1525562|entityMap|0|LINK|mutability|MUTABLE|url|http://renaud.waldura.com/doc/java/final-keyword.shtml|1|http://www.javaspecialists.eu/archive/Issue096.html^0|H|5|0|0|0|0|6|5|0|0|5|5|1O|J|S|8|0|0|0|C|5|15|L|1|0^^$0|@$1|2|3|4|5|6|7|17|8|@$9|18|A|19|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1A|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|1B|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|1C|8|@]|D|@]|E|$]]|$1|M|3|N|5|6|7|1D|8|@$9|1E|A|1F|B|C]]|D|@]|E|$]]|$1|O|3|P|5|L|7|1G|8|@]|D|@]|E|$]]|$1|Q|3|R|5|6|7|1H|8|@$9|1I|A|1J|B|C]|$9|1K|A|1L|B|S]]|D|@$9|1M|A|1N|1|1O]]|E|$]]|$1|T|3|U|5|6|7|1P|8|@]|D|@]|E|$]]|$1|V|3|W|5|6|7|1Q|8|@$9|1R|A|1S|B|C]]|D|@$9|1T|A|1U|1|1V]]|E|$]]|$1|X|3|-4|5|6|7|1W|8|@]|D|@]|E|$]]]|Y|$Z|$5|10|11|12|E|$13|14]]|15|$5|10|11|12|E|$13|16]]]]

Disregard the quote. There's little to no benefit from making your code blotted with <code>final</code>'s every now and then. Author aimed for a good practice, but in large code-bases, seeing everything made final rather obscures the intent, making reading code harder and more obscure - and may give little to no benefit. 

<h2>Two approaches</h2>

Generally though, there are two schools. Choose yours:

<ol>
<li>AGAINST, unless really needed</li>
</ol>

One is NOT to use <code>final</code>, unless you REALLY want those reading the code you wrote to know that this field is special in some way and is not to be trifled with.

<ol>
<li>For, there's never a bad place to use final!</li>
</ol>

The other is enamored with <code>final</code> and wants it everywhere. It's less prevalent. <a href="http://renaud.waldura.com/doc/java/final-keyword.shtml" rel="nofollow">Renauld Waldura</a> makes for an excellent propagator of the idea. Read his linked entry, titled "Final word on final keyword", it's a good and in-depth read.

<h2>May depend on Java you use</h2>

On my part I'd just want you to know that <code>final</code> changed, and doesn't ALWAYS mean unmutable, as you can read in <a href="http://www.javaspecialists.eu/archive/Issue096.html" rel="nofollow">Heinz Kabutz' Java Specialist Newsletter</a>. He takes you through how it worked in different Javas, feel free to take his code and check the Java you use.

From the famous book <a href="https://rads.stackoverflow.com/amzn/click/com/0321349601" rel="noreferrer" rel="nofollow noreferrer">Java Concurrency in Practice</a> chapter 3.4.1 Final fields

<blockquote>
 Just as it is a good practice to make all fields private unless they
 need greater visibility[EJ Item 12] , it is a good practice to make
 all fields final unless they need to be mutable.
</blockquote>

My understanding of final references in Java : A final reference/ field just prevents the the field from getting re initialized but if it references a mutable object , we can still change its state rendering it mutable . So I am having difficulty understanding the above quote . What do you think ?

Do final fields really prevent mutability 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。

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摘自著名著作“第3.4.1章最终字段”正如使所有字段都是私有的良好实践，除非它们需要更大的visibilityEJ项目12，但是最好的做法是使所有字段成为最终的，除非它们需要是可变的。我对Java中的最终引用的理解是:最后的引用/字段只会阻止该字段重新初始化，但是如果它引用了一个可变的对象，我们仍然可以更改它的状态呈现...

问最后的字段真的可以防止Java中的易变性吗？
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问最后的字段真的可以防止Java中的易变性吗？
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