blocks|key|3705970|text|像这样|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3705971|char+arr[]=new+char[30];+//declares+an+array+which+can+hold+30+characters
++++arr[2]='a';
++++arr[20]='b';|code-block|syntax|javascript|3705972|但是如果您不想指定长度，那么arraylist可以帮助您完成任务，因为在Java中数组的大小总是固定的|3705973|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|$]]

like this

<pre><code>char arr[]=new char[30]; //declares an array which can hold 30 characters
 arr[2]='a';
 arr[20]='b';
</code></pre>

but if you don't want to specify the length,than arraylist is something which will help you to accomplish your task because array's size is always fixed in Java

blocks|key|5173380|text|Java和JavaScript是两种不同的语言。你不能在这两个地方做同样的事情|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|5173381|在Java中，您可以编写|5173382|char[]+arr=new+char[2];
arr[0]='a';
arr[1]='b';|code-block|syntax|javascript|5173383|如果不想指定长度，可在List+Java中使用|BOLD|5173384|List<Character>+list=new+ArrayList<>();
list.add('a');
list.add('b');|5173385|entityMap^0|0|4|5|A|0|1|4|0|0|B|4|G|4|B|4|G|4|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@$9|U|A|V|B|C]|$9|W|A|X|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Y|8|@$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|11|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|12|8|@$9|13|A|14|B|O]|$9|15|A|16|B|O]|$9|17|A|18|B|C]|$9|19|A|1A|B|C]]|D|@]|E|$]]|$1|P|3|Q|5|J|7|1B|8|@]|D|@]|E|$K|L]]|$1|R|3|-4|5|6|7|1C|8|@]|D|@]|E|$]]]|S|$]]

<code>Java</code> and <code>JavaScript</code> are two deferent languages. you can't do same thing in both

In <code>Java</code> you can write

<pre><code>char[] arr=new char[2];
arr[0]='a';
arr[1]='b';
</code></pre>

If you don't want to specific the length, you can use <code>List</code> in <code>Java</code>

<pre><code>List&lt;Character&gt; list=new ArrayList&lt;&gt;();
list.add('a');
list.add('b');
</code></pre>

blocks|key|5173425|text|当你想要一个字符数组时，你可以这样做：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5173426|char[]+array+=+new+char[30];
array[2]+=+'a';
array[20]+=+'b';|code-block|syntax|javascript|5173427|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|$]]

When you want an array of characters you can do it like this:

<pre><code>char[] array = new char[30];
array[2] = 'a';
array[20] = 'b';
</code></pre>

blocks|key|3706084|text|这取决于，如果你要使用一个固定大小的数组，你可以使用：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3706085|char+myarray[]=new+char[50];
myarray[2]='a';
myarray[20]='b';|code-block|syntax|javascript|3706086|如果要动态更改数组的大小，可以使用类似于ArrayList的集合(查看文档)，并在所需位置插入字符|3706087|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|$]]

It depends, if you are going to use an array of a fixed size you can use:

<pre><code>char myarray[]=new char[50];
myarray[2]='a';
myarray[20]='b';
</code></pre>

If you are going to change the size of the array dynamically you can use a Collection like an ArrayList (look at the doc) and insert chars in the positions you want

blocks|key|1296726|text|如果你不想指定长度，你可以像这样使用List：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1296727|List<Character>+list+=+new+ArrayList<>();
list.add('a');
list.add('b');|code-block|syntax|javascript|1296728|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|$]]

If you don't want to specific length you can use List like this:

<pre><code>List&lt;Character&gt; list = new ArrayList&lt;&gt;();
list.add('a');
list.add('b');
</code></pre>

blocks|key|5173483|text|你不能。Java之于Javascript就像火腿之于仓鼠。没有理由相信它们具有相同的语法。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5173484|如果需要稀疏数组，请使用Map|offset|length|style|CODE|5173485|final+Map<Integer,+Character>+a+=+new+LinkedHashMap<>();
a.put(2,+'a');
a.put(20,+'b');|code-block|syntax|javascript|5173486|entityMap^0|0|C|3|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@$D|Q|E|R|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|S|8|@]|9|@]|A|$K|L]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

You cannot. Java is to Javascript as ham is to hamster. There is no reason to believe they have the same syntax. 

If you want a sparse array, use a <code>Map</code>:

<pre><code>final Map&lt;Integer, Character&gt; a = new LinkedHashMap&lt;&gt;();
a.put(2, 'a');
a.put(20, 'b');
</code></pre>

blocks|key|1389599|text|正如其他人已经指出的:+Java和JavaScript是两个不同的东西。对于可变大小的容器，有Java+collections+framework。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1389600|但是选择哪一个呢？这取决于你需要什么。从你的问题中，我可以想象两种情况：|1389601|可变大小的索引容器：|1389602|基本上是一个类似数组的列表。在Java语言中，除了ArrayList使用的其他list实现之外，还使用了以下内容：|style|CODE|1389603|List<Character>+myList+=+new+ArrayList<Character>();+

//+insert+element+at+the+end+of+the+list
myList.add('a');

//+insert+element+at+specific+position+in+list
myList.add(1,+'b');

//+this+will+fail,+because+there's+no+element+at+position+2!!!
myList.add(3,+'c')|code-block|syntax|javascript|1389604|一个用于从整数映射到字符的容器：|1389605|在java中有很多map实现，我建议使用HashMap，如下所示：|1389606|Map<Integer,Character>+myMap+=+new+HashMap<Integer,Character>();+

//+insert+mappings+int+->+char
myMap.put(0,+'a');
myMap.put(1,+'b');
myMap.put(20,+'c');|1389607|每个容器都有不同的用途。我建议阅读Java+collections+tutorial，以便能够选择最合适的。还可以看看tucuxi的答案，因为他提出了一个模拟所需行为的解决方案，但考虑到(正如他自己所说的)这不是java的做事方式！|BOLD|1389608|entityMap|0|LINK|mutability|MUTABLE|url|http://en.wikipedia.org/wiki/Java_collections_framework|1|http://docs.oracle.com/javase/tutorial/collections/^0|1B|Q|0|0|0|0|P|9|0|0|0|K|7|0|0|2V|D|H|P|1|0^^$0|@$1|2|3|4|5|6|7|19|8|@]|9|@$A|1A|B|1B|1|1C]]|C|$]]|$1|D|3|E|5|6|7|1D|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|1E|8|@]|9|@]|C|$]]|$1|H|3|I|5|6|7|1F|8|@$A|1G|B|1H|J|K]]|9|@]|C|$]]|$1|L|3|M|5|N|7|1I|8|@]|9|@]|C|$O|P]]|$1|Q|3|R|5|6|7|1J|8|@]|9|@]|C|$]]|$1|S|3|T|5|6|7|1K|8|@$A|1L|B|1M|J|K]]|9|@]|C|$]]|$1|U|3|V|5|N|7|1N|8|@]|9|@]|C|$O|P]]|$1|W|3|X|5|6|7|1O|8|@$A|1P|B|1Q|J|Y]]|9|@$A|1R|B|1S|1|1T]]|C|$]]|$1|Z|3|-4|5|6|7|1U|8|@]|9|@]|C|$]]]|10|$11|$5|12|13|14|C|$15|16]]|17|$5|12|13|14|C|$15|18]]]]

As others already pointed out: Java and JavaScript are two different things. For containers with variable size there is the <a href="http://en.wikipedia.org/wiki/Java_collections_framework" rel="nofollow">Java collections framework</a>.

But wich to choose? That depends on what you need. From your question I can imagine two cases:

<h3>a variable sized, indexed container:</h3>

basically an array-like list. In Java there's besides other list implementations the <code>ArrayList</code> used as follows:

<pre><code>List&lt;Character&gt; myList = new ArrayList&lt;Character&gt;(); 

// insert element at the end of the list
myList.add('a');

// insert element at specific position in list
myList.add(1, 'b');

// this will fail, because there's no element at position 2!!!
myList.add(3, 'c')
</code></pre>

<h3>a container for mappings from integer to character:</h3>

In java there's lots of map implementations, I propose the <code>HashMap</code>, used like this:

<pre><code>Map&lt;Integer,Character&gt; myMap = new HashMap&lt;Integer,Character&gt;(); 

// insert mappings int -&gt; char
myMap.put(0, 'a');
myMap.put(1, 'b');
myMap.put(20, 'c');
</code></pre>

Each Container serves a different purpose. I advise reading the <a href="http://docs.oracle.com/javase/tutorial/collections/" rel="nofollow">Java collections tutorial</a> to be able to choose the best fitting one. Also take a look at tucuxi's answer, as he presented a solution wich simulates the desired beahviour but consider that (as he said himself) this is not the java way of doing things!

blocks|key|1389648|text|你可以随时写你自己的。您将不会了解语法，但是大部分的风格仍然存在。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1389649|请注意，从效率的角度来看，这是一个糟糕的想法。您可以通过学习“Java方式”来编写更好的代码。这对所有的语言都是正确的:对语言的粒度进行编程肯定会给你带来痛苦。|1389650|但下面是代码：|1389651|class+MyArray<T>+extends+ArrayList<T>+{
++++public+MyArray<T>()+{+super();+}
++++public+void+add(int+i,+T+value)+{+
++++++++if+(size()+<+i)+{+
++++++++++++ensureCapacity(i%2B1);+//+grow+at+most+once+instead+of+multiple+times+
++++++++++++while+(size()+<+i))+{+
++++++++++++++++add(null);+//+extend+with+a+null+object
++++++++++++}
++++++++++++add(value);
++++++++}+else+{
++++++++++++add(i,+value);
++++++++}
++++}++++++++++++
}|code-block|syntax|javascript|1389652|现在，您可以将普通ArrayList与MyArray的实例进行比较|offset|length|style|CODE|1389653|ArrayList<Character>+a+=+new+ArrayList<>();
MyArray<Character>+b+=+new+MyArray<>()
a.add(10,+'X');+//+IndexOutOfBoundsException,+size+is+0
b.add(10,+'X');+//+no+exception+-+you+get+[10+x+null,+'X']
b.get(10);++++++//+returns+'X'|1389654|请记住，JavaScript数组可以由任意对象索引，而不仅仅是整数--而且JavaScript+VM尽可能使用数字索引的数组。对于任意索引，您需要使用Java+HashMap|1389655|class+MyArray2<T>+extends+HashMap<Object,+T>+{
++++public+MyArray2<T>()+{+super();+}
++++public+void+add(Object+o,+T+value)+{+set(o,+value);+}
}|1389656|然后，您可以将其用作：|1389657|MyArray2<Character>+c+=+new+MyArray2<>()
c.add("anything",+'?');
c.get("anything");+//+returns+'?'|1389658|entityMap^0|0|0|0|0|9|9|J|7|0|0|28|7|0|0|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|13|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|14|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|15|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|16|8|@$M|17|N|18|O|P]|$M|19|N|1A|O|P]]|9|@]|A|$]]|$1|Q|3|R|5|H|7|1B|8|@]|9|@]|A|$I|J]]|$1|S|3|T|5|6|7|1C|8|@$M|1D|N|1E|O|P]]|9|@]|A|$]]|$1|U|3|V|5|H|7|1F|8|@]|9|@]|A|$I|J]]|$1|W|3|X|5|6|7|1G|8|@]|9|@]|A|$]]|$1|Y|3|Z|5|H|7|1H|8|@]|9|@]|A|$I|J]]|$1|10|3|-4|5|6|7|1I|8|@]|9|@]|A|$]]]|11|$]]

You can always write your own. You will not get the syntax, but most of the flavor will still be there.

Note that, efficiency-wise, this is a terrible idea. You can write much better code by learning "the Java way" of doing things. This is true of all languages: programming against the grain of the language is sure to cause you pain.

But here is the code:

<pre><code>class MyArray&lt;T&gt; extends ArrayList&lt;T&gt; {
 public MyArray&lt;T&gt;() { super(); }
 public void add(int i, T value) { 
 if (size() &lt; i) { 
 ensureCapacity(i+1); // grow at most once instead of multiple times 
 while (size() &lt; i)) { 
 add(null); // extend with a null object
 }
 add(value);
 } else {
 add(i, value);
 }
 } 
}
</code></pre>

Now you can compare a garden-variety <code>ArrayList</code> with an instance of <code>MyArray</code>:

<pre><code>ArrayList&lt;Character&gt; a = new ArrayList&lt;&gt;();
MyArray&lt;Character&gt; b = new MyArray&lt;&gt;()
a.add(10, 'X'); // IndexOutOfBoundsException, size is 0
b.add(10, 'X'); // no exception - you get [10 x null, 'X']
b.get(10); // returns 'X'
</code></pre>

Bear in mind that JavaScript arrays can be indexed by arbitrary objects and not only integers -- but that the JavaScript VM tries to use numerically-indexed arrays if at all possible. For arbitrary indexing, you would need to use a Java <code>HashMap</code>:

<pre><code>class MyArray2&lt;T&gt; extends HashMap&lt;Object, T&gt; {
 public MyArray2&lt;T&gt;() { super(); }
 public void add(Object o, T value) { set(o, value); }
}
</code></pre>

You would then use as:

<pre><code>MyArray2&lt;Character&gt; c = new MyArray2&lt;&gt;()
c.add("anything", '?');
c.get("anything"); // returns '?'
</code></pre>

In JavaScript, I can write code like this:

<pre><code>var a = new Array();
a[2] = 'a';
a[20] = 'b';
</code></pre>

and this would not work on Java, the point is I don't want to specific the exact length for it.

How could I keep this happy style when writing java?

How to make a Java array behave like a JavaScript array?

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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在JavaScript中，我可以像这样编写代码：var a = new Array();a[2] = 'a';a[20] = 'b';这在Java上是行不通的，关键是我不想为它指定确切的长度。如何在编写java时保持这种愉快的风格？

问如何让Java数组表现得像JavaScript数组？
EN

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问如何让Java数组表现得像JavaScript数组？EN