blocks|key|599202|text|以下是您的代码的关键行：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|599203|+Outerclass+c+=+new+Outerclass+();

+++++InnerClass+e+=+new+InnerClass();|code-block|syntax|javascript|599204|那行不通的。你会得到一个编译错误。|599205|由于InnerClass是一个内部类，因此需要在其封闭类(即OuterClass)的一个实例的上下文中实例化它。如下所示：|offset|length|style|CODE|599206|+Outerclass+c+=+new+Outerclass+();

+++++InnerClass+e+=+c.new+InnerClass();|599207|c.new+...表单称为限定类实例创建表达式；请参见JLS+15.9。|599208|备注：|599209|599210|如果创建内部类的代码是在外部类的实例的上下文中(例如，它在外部类的实例方法中)，那么你不需要这样限定new。|ordered-list-item|599211|如果InnerClass是static，这也是不必要的。但是InnerClass是一个嵌套类，而不是一个内部类。根据标准的Java+terminology.|599212|599213|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.9^0|0|0|0|2|A|U|A|0|0|0|9|R|8|0|0|0|0|1E|3|0|2|A|D|6|U|A|0|0^^$0|@$1|2|3|4|5|6|7|19|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|1A|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|1B|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|1C|8|@$K|1D|L|1E|M|N]|$K|1F|L|1G|M|N]]|9|@]|A|$]]|$1|O|3|P|5|D|7|1H|8|@]|9|@]|A|$E|F]]|$1|Q|3|R|5|6|7|1I|8|@$K|1J|L|1K|M|N]]|9|@$K|1L|L|1M|1|1N]]|A|$]]|$1|S|3|T|5|6|7|1O|8|@]|9|@]|A|$]]|$1|U|3|-4|5|6|7|1P|8|@]|9|@]|A|$]]|$1|V|3|W|5|X|7|1Q|8|@$K|1R|L|1S|M|N]]|9|@]|A|$]]|$1|Y|3|Z|5|X|7|1T|8|@$K|1U|L|1V|M|N]|$K|1W|L|1X|M|N]|$K|1Y|L|1Z|M|N]]|9|@]|A|$]]|$1|10|3|-4|5|6|7|20|8|@]|9|@]|A|$]]|$1|11|3|-4|5|6|7|21|8|@]|9|@]|A|$]]]|12|$13|$5|14|15|16|A|$17|18]]]]

Here are the key lines of your code:

<pre><code> Outerclass c = new Outerclass ();

 InnerClass e = new InnerClass();
</code></pre>

That won't work. You will get a compilation error.

Since <code>InnerClass</code> is an inner class, it needs to be instantiated in the context of an instance of its enclosing class (i.e. <code>OuterClass</code>). Like this:

<pre><code> Outerclass c = new Outerclass ();

 InnerClass e = c.new InnerClass();
</code></pre>

The <code>c.new ...</code> form is called a qualified class instance creation expression; see <a href="http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.9" rel="nofollow">JLS 15.9</a>.

Notes:

<ol>
<li>If the code that creates the inner class is in the context of an instance of the outer class (e.g. it is in an instance method of the outer class) then you don't need to qualify the <code>new</code> like that.</li>
<li>If the <code>InnerClass</code> is <code>static</code> this isn't necessary either. But then <code>InnerClass</code> is a nested class not an inner class ... according to the standard Java terminology.</li>
</ol>

blocks|key|3776747|text|内部类的实例只能存在于外部类的实例中。(有关静态和非静态内部类之间的区别，请参阅this+answer了解更多信息)。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|3776748|这意味着您在外部对象中创建内部对象。您可以将其视为创建和包含内部对象的外部对象(因此得名inner)。|style|CODE|3776749|下面是一个例子：|3776750|import+java.util.ArrayList;

public+class+OuterClass+{
++++static+ArrayList<InnerClass>+innerClasses+=+new+ArrayList<InnerClass>();

++++public+static+void+main(String[]+args)+{
++++++++OuterClass+oc1+=+new+OuterClass();
++++++++OuterClass.InnerClass+ic1+=++oc1.new+InnerClass();
++++++++OuterClass.InnerClass+ic2+=++oc1.new+InnerClass();
++++++++innerClasses.add(ic1);
++++++++innerClasses.add(ic2);++++++
++++++++System.out.println(innerClasses.size());
++++}
++++class+InnerClass+{

++++}
}|code-block|syntax|javascript|3776751|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/70324/java-inner-class-and-static-nested-class/70358#70358^0|14|B|0|0|18|5|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@$A|X|B|Y|1|Z]]|C|$]]|$1|D|3|E|5|6|7|10|8|@$A|11|B|12|F|G]]|9|@]|C|$]]|$1|H|3|I|5|6|7|13|8|@]|9|@]|C|$]]|$1|J|3|K|5|L|7|14|8|@]|9|@]|C|$M|N]]|$1|O|3|-4|5|6|7|15|8|@]|9|@]|C|$]]]|P|$Q|$5|R|S|T|C|$U|V]]]]

An instance of an inner class can only exist within an instance of an outer class. (For a distinction between static and non-static inner classes, see <a href="https://stackoverflow.com/questions/70324/java-inner-class-and-static-nested-class/70358#70358">this answer</a> for more info).

What this means is that you create inner objects within outer objects. You can think of it as the outer objects creating and containing the inner objects (hence the name <code>inner</code>)

Here's an example:

<pre><code>import java.util.ArrayList;

public class OuterClass {
 static ArrayList&lt;InnerClass&gt; innerClasses = new ArrayList&lt;InnerClass&gt;();

 public static void main(String[] args) {
 OuterClass oc1 = new OuterClass();
 OuterClass.InnerClass ic1 = oc1.new InnerClass();
 OuterClass.InnerClass ic2 = oc1.new InnerClass();
 innerClasses.add(ic1);
 innerClasses.add(ic2); 
 System.out.println(innerClasses.size());
 }
 class InnerClass {

 }
}
</code></pre>

blocks|key|5889147|text|首先，我认为在你开始跑步之前，你应该学习如何走路：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5889148|public+Outerclass|code-block|syntax|javascript|5889149|应该是|5889150|public+class+Outerclass|5889151|内部也是如此！|5889152|其次，所有代码的最后部分都应该在Ourclass中的main()方法中。|offset|length|style|CODE|5889153|第三，不，你不能那样使用内部类，这就是为什么这些类是内部的。如果你想从main()内部或外部类外部使用内部类，你必须使用外部的实例来访问它们，就像访问任何其他实例成员一样-你不能直接访问它：|5889154|++++++++Outerclass+oc+=+new+Outerclass();
++++++++Outerclass.InnerClass+in+=+oc.new+InnerClass();|5889155|entityMap^0|0|0|0|0|0|Q|6|0|Z|6|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]]|$1|K|3|L|5|6|7|12|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|13|8|@$O|14|P|15|Q|R]]|9|@]|A|$]]|$1|S|3|T|5|6|7|16|8|@$O|17|P|18|Q|R]]|9|@]|A|$]]|$1|U|3|V|5|D|7|19|8|@]|9|@]|A|$E|F]]|$1|W|3|-4|5|6|7|1A|8|@]|9|@]|A|$]]]|X|$]]

First, I think that you should learn how to walk before you start running:

<pre><code>public Outerclass
</code></pre>

should be

<pre><code>public class Outerclass
</code></pre>

same with inner!

Second, all the last portion of your code should be in a <code>main()</code> method INSIDE Ourclass.

And third, no, you cannot use inner class like that, that's why these classes are inner. If you want to use inner classes from inside <code>main()</code> or from outside the outer class you have to use an instance of outer in order to access them, same like accessing any other instance member - you can't access it directly:

<pre><code> Outerclass oc = new Outerclass();
 Outerclass.InnerClass in = oc.new InnerClass();
</code></pre>

blocks|key|5889178|text|既然InnerClass需要维护对OuterClass成员的引用，我想知道为什么不将ArrayList<InnerClass>放在OuterClass中。如果它们是以这种方式组成的，那么让OuterClass“管理”列表，并只给它提供返回InnerClass实例列表等的访问方法就更有意义了。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|5889179|所以就像这样：|5889180|public+class+OuterClass
{
+++private+List<InnerClass>+innerClassInstances+=+new+ArrayList<>;

+++public+void+addInnerInstances(int+count)
+++{
++++++for(int+j+=+0+;+j+<+count;+j%2B%2B)
++++++{
+++++++++InnerClass+e+=+new+InnerClass();
+++++++++innerClassInstances.add(e);
++++++}
+++}

+++public+List<InnerClass>+getInnerClassInstances()
+++{
+++++++return+innerClassInstances;
+++}

+++public+class+InnerClass
+++{
+++++//...
+++}
}

+++//in+your+main+class+or+wherever
+++List<Outerclass>+olist;

+++olist=+new+ArrayList<Outerclass>();
+++for+(int+i+=+0;+i+<+3;+i%2B%2B)+
+++{
++++++Outerclass+c+=+new+Outerclass+();
++++++c.addInnerInstances(4);
++++++olist.add(c);
+++}|code-block|syntax|javascript|5889181|您不能像现在这样使用new单独创建InnerClass，您说的是它需要访问其OuterClass实例的成员，而且正如您在代码中看到的那样，对于每个new+InnerClass()，您从未以任何方式指定它的OuterClass实例是什么。|5889182|entityMap^0|2|A|H|A|16|L|1T|A|2M|A|3B|A|0|0|0|A|3|H|A|12|A|21|G|2U|A|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|C]|$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|13|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|14|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|15|8|@$9|16|A|17|B|C]|$9|18|A|19|B|C]|$9|1A|A|1B|B|C]|$9|1C|A|1D|B|C]|$9|1E|A|1F|B|C]]|D|@]|E|$]]|$1|O|3|-4|5|6|7|1G|8|@]|D|@]|E|$]]]|P|$]]

Given that the <code>InnerClass</code> needs to maintain reference to the members of the <code>OuterClass</code>, I wonder why aren't you putting the <code>ArrayList&lt;InnerClass&gt;</code> inside <code>OuterClass</code>. If they're composed in that way it makes much more sense to have the list 'managed' by the <code>OuterClass</code> and just give it access methods to return the list of <code>InnerClass</code> instances etc.

So something like this: 

<pre><code>public class OuterClass
{
 private List&lt;InnerClass&gt; innerClassInstances = new ArrayList&lt;&gt;;

 public void addInnerInstances(int count)
 {
 for(int j = 0 ; j &lt; count; j++)
 {
 InnerClass e = new InnerClass();
 innerClassInstances.add(e);
 }
 }

 public List&lt;InnerClass&gt; getInnerClassInstances()
 {
 return innerClassInstances;
 }

 public class InnerClass
 {
 //...
 }
}

 //in your main class or wherever
 List&lt;Outerclass&gt; olist;

 olist= new ArrayList&lt;Outerclass&gt;();
 for (int i = 0; i &lt; 3; i++) 
 {
 Outerclass c = new Outerclass ();
 c.addInnerInstances(4);
 olist.add(c);
 }
</code></pre>

You cannot create the <code>InnerClass</code> on its own with <code>new</code> as you're doing, you are saying that it needs to access the members of its <code>OuterClass</code> instance, and as you can see in your code, for each <code>new InnerClass()</code> you are never specifying in any way what is the <code>OuterClass</code> instance for it.

blocks|key|599262|text|如果您有用于数据存储的嵌套类，则对答案#2稍加改进，意味着您有一个外部类的构造函数，该构造函数自动为内部类生成数量可变的数组成员，如树结构。这个解决方案实际上是一种变通方法，它使用一个已定义的成员-+ArrayList+-它可以在以后扩展，而不是在OuterClass中直接定义InnerClass[]数组，如果它不是静态的，就不会工作。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|599263|public+class+OuterClass
{
++++private+int+NumberInnerClassInstances;+++++++
++++//+...+other+members+of+OuterClass
++++ArrayList<InnerClass>+innerClassInstances+=+new+ArrayList<>();

++++OuterClass(+input+vars+...)++{
++++++++//+calculate+the+NumberInnerClassInstances+needed
++++++++for(int+i+=+0+;+j+<+NumberInnerClassInstances;+i%2B%2B)+{
++++++++++++OuterClass.InnerClass+in+=+this.new+InnerClass(i);
++++++++++++innerClassInstances.add(in);
++++++++}
++++}

++++public+class+InnerClass
++++{
++++++++int+icvar;
++++++++InnerClass(int+i)+{
++++++++++++//...construct+the+Inner+Class+Member+#i
++++++++++++//+can+access+the+members+of+OuterClass
++++++++}
++++}
}|code-block|syntax|javascript|599264|然后，您可以从外部使用get访问InnerClass实例：|599265|oc+=+new+OuterClass(+vars+...)
var+=+oc.InnerClassInstances.get(i).icvar|599266|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

A litte refinement for answer #2, if you have nested classes for data storage, means that you have an constructor for the outer class that automatically generates a variable number of array members for the inner class like a tree structure. This solution is practically a workaround which uses one defined member - an ArrayList - which can be expanded later instead of a direct definition of an InnerClass[] array inside the OuterClass, which won't work if its not static.

<pre><code>public class OuterClass
{
 private int NumberInnerClassInstances; 
 // ... other members of OuterClass
 ArrayList&lt;InnerClass&gt; innerClassInstances = new ArrayList&lt;&gt;();

 OuterClass( input vars ...) {
 // calculate the NumberInnerClassInstances needed
 for(int i = 0 ; j &lt; NumberInnerClassInstances; i++) {
 OuterClass.InnerClass in = this.new InnerClass(i);
 innerClassInstances.add(in);
 }
 }

 public class InnerClass
 {
 int icvar;
 InnerClass(int i) {
 //...construct the Inner Class Member #i
 // can access the members of OuterClass
 }
 }
}
</code></pre>

from outside, you can then access the InnerClass Instances with get:

<pre><code>oc = new OuterClass( vars ...)
var = oc.InnerClassInstances.get(i).icvar
</code></pre>

I am relatively new to Java. I wanted to create an arraylist of an outer class and for each index of the outer class of the arraylist I want an arraylist of inner classes.

<pre><code>public Outerclass{

 //Code Here

 public InnerClass{
 //Code Here
 }
}

//My attempt at setting up the arrays
public ArrayList &lt;Outerclass&gt; olist;
public ArrayList &lt;InnerClass&gt; ilist;


 olist= new ArrayList&lt;Outerclass&gt;();
 for (int i = 0; i &lt; 3; i++) {
 Outerclass c = new Outerclass ();
 ilist = new ArrayList&lt;InnerClass&gt;();
 for(int j = 0 ; j &lt; 4; j++){
 InnerClass e = new InnerClass();
 ilist.add(e);
 }
 olist.add(c);
 }
</code></pre>

Will this work?

Arrays with outer and inner classes

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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我对Java比较陌生。我想创建一个外部类的arraylist，并且对于arraylist的外部类的每个索引，我想要一个内部类的arraylist。public Outerclass{    //Code Here    public InnerClass{    //Code Here    }}//My attemp...

问具有外部类和内部类的数组
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问具有外部类和内部类的数组EN