blocks|key|43610|text|使用final关键字：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|43611|private+final+String+name;
private+final+String+age;|code-block|syntax|javascript|43612|entityMap^0|2|5|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

With <code>final</code> keyword:

<pre><code>private final String name;
private final String age;
</code></pre>

blocks|key|43658|text|这很好，但我也会将字段设为final。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|43659|此外，我会将年龄设置为int或double，而不是字符串。|43660|entityMap^0|D|5|0|B|3|F|6|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|R|8|@]|D|@]|E|$]]]|I|$]]

This is fine but I would make the fields <code>final</code> as well.

Also I would make the age an <code>int</code> or <code>double</code> rather than a String.

blocks|key|260448|text|严格地说，您的类并不是不可变的，它只是有效地不可变。要使其不可变，您需要使用final|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|260449|private+final+String+name;
private+final+String+age;|code-block|syntax|javascript|260450|尽管差别可能看起来很微妙，it+can+make+a+significant+difference+in+a+multi-threaded+context。不可变的类本质上是线程安全的，有效不可变的类只有在安全发布的情况下才是线程安全的。|260451|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/16061030/must-all-properties-of-an-immutable-object-be-final^0|12|5|0|0|D|1S|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|Y|8|@]|D|@$9|Z|A|10|1|11]]|E|$]]|$1|M|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

Your class is not immutable strictly speaking, it is only effectively immutable. To make it immutable, you need to use <code>final</code>:

<pre><code>private final String name;
private final String age;
</code></pre>

Although the difference might seem subtle, <a href="https://stackoverflow.com/questions/16061030/must-all-properties-of-an-immutable-object-be-final">it can make a significant difference in a multi-threaded context</a>. An immutable class is inherently thread-safe, an effectively immutable class is thread safe only if it is safely published.

blocks|key|260470|text|它已经是不可变的--一旦初始化它就不能更改内容，因为您还没有创建setter方法。您可以将final关键字添加到变量中。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|260471|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 already is immutable -- you can't change the contents once you initialize it, since you haven't made setters. You might add final keywords to the variables.

blocks|key|43767|text|将所有变量设置为final，并在设置某些字段时，使其返回对新Student对象的引用，其中包含新设置的值，就像String中一样。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|43768|entityMap^0|8|5|U|7|1J|6|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|$]]

Making all variables as <code>final</code> and when setting some field, making it return the reference to the new <code>Student</code> object with the newly set value like in <code>String</code>.

blocks|key|260560|text|您只需遵循本例中显示的指导原则(谷歌的第一个结果)：http://www.javapractices.com/topic/TopicAction.do?Id=29|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|260561|entityMap|0|LINK|mutability|MUTABLE|url|http://www.javapractices.com/topic/TopicAction.do?Id=29^0|Q|1J|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]]]]

You can just follow guidelines shown in this example (first result in google):
<a href="http://www.javapractices.com/topic/TopicAction.do?Id=29" rel="nofollow">http://www.javapractices.com/topic/TopicAction.do?Id=29</a>

blocks|key|43856|text|这里有几条规则，有助于在Java中使类不可变:+1.不可变对象的状态在构造后不能被修改，任何修改都应该导致新的不可变对象。2.不可变类的所有字段都必须是final。3.必须正确构造对象，即在构造过程中不能泄漏对象引用。4.+Object必须为final，才能限制子类更改父类的不变性。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|43857|示例：|43858|public+final+class+Contacts+{

private+final+String+name;
private+final+String+mobile;

public+Contacts(String+name,+String+mobile)+{
++++this.name+=+name;
++++this.mobile+=+mobile;
}

public+String+getName(){
++++return+name;
}

public+String+getMobile(){
++++return+mobile;
}|code-block|syntax|javascript|43859|}|43860|请参阅此链接：http://javarevisited.blogspot.in/2013/03/how-to-create-immutable-class-object-java-example-tutorial.html|offset|length|43861|entityMap|0|LINK|mutability|MUTABLE|url|http://javarevisited.blogspot.in/2013/03/how-to-create-immutable-class-object-java-example-tutorial.html^0|0|0|0|0|7|2W|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|X|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|Z|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|10|8|@]|9|@$M|11|N|12|1|13]]|A|$]]|$1|O|3|-4|5|6|7|14|8|@]|9|@]|A|$]]]|P|$Q|$5|R|S|T|A|$U|V]]]]

Here are few rules, which helps to make a class immutable in Java :
1. State of immutable object can not be modified after construction, any modification should result in new immutable object.
2. All fields of Immutable class should be final.
3. Object must be properly constructed i.e. object reference must not leak during construction process.
4. Object should be final in order to restrict sub-class for altering immutability of parent class.

Example:

<pre><code>public final class Contacts {

private final String name;
private final String mobile;

public Contacts(String name, String mobile) {
 this.name = name;
 this.mobile = mobile;
}

public String getName(){
 return name;
}

public String getMobile(){
 return mobile;
}
</code></pre>

}

Refer this link : <a href="http://javarevisited.blogspot.in/2013/03/how-to-create-immutable-class-object-java-example-tutorial.html" rel="nofollow">http://javarevisited.blogspot.in/2013/03/how-to-create-immutable-class-object-java-example-tutorial.html</a>

blocks|key|43891|text|将类或变量设置为final，这就足够了|type|unstyled|depth|inlineStyleRanges|entityRanges|data|43892|Public+final+class+constants
{
++private+final+String+name;
++private+final+String+mobile;

++//+code
}|code-block|syntax|javascript|43893|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Make the class or variable as final that's more than enough

<pre><code>Public final class constants
{
 private final String name;
 private final String mobile;

 // code
}
</code></pre>

blocks|key|43940|text|将变量设为私有且不使用setter方法将适用于原始数据类型。如果我的类有任何对象集合？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|43941|使任何具有集合对象的类不可变？|43942|使用扩展集合类编写您自己的集合对象，并遵循私有变量，不使用setter方法。或者返回集合对象的克隆对象。|43943|public+final+class+Student+{

private+StudentList+names;//Which+is+extended+from+arraylist

public+Student()+{
names+=+DAO.getNamesList()//Which+will+return+All+Student+names+from+Database++its+upto+you+how+you+want+to+implement.
}

public+StudentList+getStudentList(){
return+names;//you+need+to+implement+your+own+methods+in+StudentList+class+to+iterate+your+arraylist;+or+you+can+return+Enumeration+object.
}

public+Enumeration+getStudentNamesIterator(
Enumeration+e+=+Collections.enumeration(names);
return+e;
}

public+class+StudentList+extends+ArrayList+{

}|code-block|syntax|javascript|43944|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|O|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|P|8|@]|9|@]|A|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Making variables private and no setter methods will work for primitive data types. If my class has any collection of objects?

To making any class immutable with collection object?

Write your own collection object with extends collection class and follow the private variables and no setter methods. or return clone object of your collection object.

<pre><code>public final class Student {

private StudentList names;//Which is extended from arraylist

public Student() {
names = DAO.getNamesList()//Which will return All Student names from Database its upto you how you want to implement.
}

public StudentList getStudentList(){
return names;//you need to implement your own methods in StudentList class to iterate your arraylist; or you can return Enumeration object.
}

public Enumeration getStudentNamesIterator(
Enumeration e = Collections.enumeration(names);
return e;
}

public class StudentList extends ArrayList {

}
</code></pre>

blocks|key|43977|text|在回答的基础上做了一些扩展。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|43978|final与Immutable不同，但是如果您以某种方式使用final，您可以使用它来使某些内容不可变。|offset|length|style|CODE|43979|某些类型是不可变的，因为它们表示不变的值，而不是状态可变的对象。字符串、数字等是不可变的。最后，我们的对象通常归结为最终引用不可变值的数据结构，但我们通过为相同的字段名称分配新值来更改数据结构。|43980|因此，要使某些东西真正不可变，您需要确保所有的过程都使用了final，直到您的组合树底部的每个字段都达到了每个值。否则，一些东西可能会从你的对象下改变出来，并且它不是真正的完全不可变的。|43981|entityMap^0|0|0|5|6|9|U|5|0|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@$D|P|E|Q|F|G]|$D|R|E|S|F|G]|$D|T|E|U|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|V|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|W|8|@]|9|@]|A|$]]|$1|L|3|-4|5|6|7|X|8|@]|9|@]|A|$]]]|M|$]]

Expanding on the answer a bit.

<code>final</code> is not the same as <code>Immutable</code> but you can use <code>final</code> to make certain things immutable if you use it in certain ways.

Certain types are immutable, in that they represent unchanging values rather than objects of changeable state. Strings, numbers, etc are immutable. At the end, usually our objects boil down to data structures eventually referencing immutable values, but we change the data structures by assigning new values to the same field names.

So to make something truly immutable you need to make sure that final is used all the way down, until you reach every field reaching every value at the base of your composition tree. Otherwise something could change out from under your the object and it isn't really fully immutable.

My goal is to make a Java object immutable. I have a class <code>Student</code>. I coded it in the following way to achieve immutability:

<pre><code>public final class Student {

private String name;
private String age;

public Student(String name, String age) {
 this.name = name;
 this.age = age;
}

public String getName() {
 return name;
}

public String getAge() {
 return age;
}

}
</code></pre>

My question is, what is the best way to achieve immutability for the <code>Student</code> class?

Make immutable Java object

数据结构

Java

我的目标是使Java对象不可变。我有一个Student类。我用以下方式对它进行了编码，以实现不变性：public final class Student {private String name;private String age;public Student(String name, String age) {  ...

问使Java对象成为不可变的
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