blocks|key|742384|text|是的，it+is+safe+to+convert+an+ArrayList+to+an+Array。这是不是一个好主意取决于你的预期用途。您需要ArrayList提供的操作吗？如果是这样，请将其保留为ArrayList。否则，请转身离开！|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|742385|ArrayList<Integer>+foo+=+new+ArrayList<Integer>();
foo.add(1);
foo.add(1);
foo.add(2);
foo.add(3);
foo.add(5);
Integer[]+bar+=+foo.toArray(new+Integer[foo.size()]);
System.out.println("bar.length+=+"+%2B+bar.length);|code-block|syntax|javascript|742386|输出|742387|bar.length+=+5|742388|entityMap|0|LINK|mutability|MUTABLE|url|http://download.oracle.com/javase/6/docs/api/java/util/ArrayList.html#toArray%2528%2529|1|http://download.oracle.com/javase/6/docs/api/java/util/ArrayList.html^0|S|9|18|5|20|9|2S|9|3|1A|0|20|9|1|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|C]]|D|@$9|17|A|18|1|19]|$9|1A|A|1B|1|1C]]|E|$]]|$1|F|3|G|5|H|7|1D|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1E|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|1F|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|1G|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]|W|$5|R|S|T|E|$U|X]]]]

Yes <a href="http://download.oracle.com/javase/6/docs/api/java/util/ArrayList.html#toArray%28%29" rel="noreferrer">it is safe to convert an <code>ArrayList</code> to an <code>Array</code></a>. Whether it is a good idea depends on your intended use. Do you need the operations that <a href="http://download.oracle.com/javase/6/docs/api/java/util/ArrayList.html" rel="noreferrer"><code>ArrayList</code></a> provides? If so, keep it an <code>ArrayList</code>. Else convert away!

<pre><code>ArrayList&lt;Integer&gt; foo = new ArrayList&lt;Integer&gt;();
foo.add(1);
foo.add(1);
foo.add(2);
foo.add(3);
foo.add(5);
Integer[] bar = foo.toArray(new Integer[foo.size()]);
System.out.println("bar.length = " + bar.length);
</code></pre>

outputs

<pre><code>bar.length = 5
</code></pre>

blocks|key|526100|text|这是最好的方法(IMHO)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|526101|List<String>+myArrayList+=+new+ArrayList<String>();
//.....
String[]+myArray+=+myArrayList.toArray(new+String[myArrayList.size()]);|code-block|syntax|javascript|526102|这段代码也可以工作：|526103|String[]+myArray+=+myArrayList.toArray(new+String[0]);|526104|但效率较低:字符串数组创建了两次:第一次创建长度为零的数组，然后创建、填充并返回实际大小的数组。因此，如果您知道所需的大小(来自list.size())，那么您应该创建足够大的数组来放置所有元素。在这种情况下，它不会被重新分配。|offset|length|style|CODE|526105|entityMap^0|0|0|0|0|1S|B|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@$M|X|N|Y|O|P]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

This is the best way (IMHO).

<pre><code>List&lt;String&gt; myArrayList = new ArrayList&lt;String&gt;();
//.....
String[] myArray = myArrayList.toArray(new String[myArrayList.size()]);
</code></pre>

This code works also:

<pre><code>String[] myArray = myArrayList.toArray(new String[0]);
</code></pre>

But it less effective: the string array is created twice: first time zero-length array is created, then the real-size array is created, filled and returned. So, if since you know the needed size (from <code>list.size()</code>) you should create array that is big enough to put all elements. In this case it is not re-allocated.

blocks|key|525957|text|ArrayList<String>+myArrayList+=+new+ArrayList<String>();
...
String[]+myArray+=+myArrayList.toArray(new+String[0]);|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|525958|这是不是一个“好主意”真的取决于你的用例。|unstyled|525959|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|J|8|@]|9|@]|A|$]]|$1|G|3|-4|5|F|7|K|8|@]|9|@]|A|$]]]|H|$]]

<pre><code>ArrayList&lt;String&gt; myArrayList = new ArrayList&lt;String&gt;();
...
String[] myArray = myArrayList.toArray(new String[0]);
</code></pre>

Whether it's a "good idea" would really be dependent on your use case.

blocks|key|742473|text|假设v是一个ArrayList：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|742474|String[]+x+=+(String[])+v.toArray(new+String[0]);|code-block|syntax|javascript|742475|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|$]]

assuming v is a ArrayList:

<pre><code>String[] x = (String[]) v.toArray(new String[0]);
</code></pre>

blocks|key|742532|text|ArrayList<String>+a+=+new+ArrayList<String>();
a.add(+"test"+);
@SuppressWarnings(+"unused")
Object[]+array+=+a.toArray();|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|742533|这取决于您想要实现什么，如果您稍后需要操作数组，那么它将比将字符串保留在ArrayList中花费更多的精力。您还可以通过list.get(+index+);的ArrayList进行随机访问|unstyled|offset|length|style|CODE|742534|entityMap^0|0|1O|I|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|N|8|@$G|O|H|P|I|J]]|9|@]|A|$]]|$1|K|3|-4|5|F|7|Q|8|@]|9|@]|A|$]]]|L|$]]

<pre><code>ArrayList&lt;String&gt; a = new ArrayList&lt;String&gt;();
a.add( "test" );
@SuppressWarnings( "unused")
Object[] array = a.toArray();
</code></pre>

It depends on what you want to achieve if you need to manipulate the array later it would cost more effort than keeping the string in the ArrayList. You have also random access with an ArrayList by <code>list.get( index );</code>

blocks|key|526139|text|Collection接口包括将新集合转换为数组的toArray()方法。这种方法有两种形式。无参数版本将在对象数组中返回集合的元素:公共对象toArray()。返回的数组不能强制转换为任何其他数据类型。这是最简单的版本。第二个版本要求您传入想要返回的数组的数据类型:+public+Object+toArray(Object+ToArray+)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|526140|+public+static+void+main(String[]+args)+{++
+++++++++++List<String>+l=new+ArrayList<String>();++
+++++++++++l.add("A");++
+++++++++++l.add("B");++
+++++++++++l.add("C");++
+++++++++++Object+arr[]=l.toArray();++
+++++++++++for(Object+a:arr)++
+++++++++++{++
++++++++++++++++String+str=(String)a;++
++++++++++++++++System.out.println(str);++
+++++++++++}++
++++++}++|code-block|syntax|javascript|526141|有关参考，请参阅此链接http://techno-terminal.blogspot.in/2015/11/how-to-obtain-array-from-arraylist.html|offset|length|526142|entityMap|0|LINK|mutability|MUTABLE|url|http://techno-terminal.blogspot.in/2015/11/how-to-obtain-array-from-arraylist.html^0|0|0|B|2A|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@$I|V|J|W|1|X]]|A|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

The Collection interface includes the toArray() method to convert a new collection into an array. There are two forms of this method. The no argument version will return the elements of the collection in an Object array: public Object[ ] toArray(). The returned array cannot cast to any other data type. This is the simplest version. The second version requires you to pass in the data type of the array you’d like to return: public Object [ ] toArray(Object type[ ]). 

<pre><code> public static void main(String[] args) { 
 List&lt;String&gt; l=new ArrayList&lt;String&gt;(); 
 l.add("A"); 
 l.add("B"); 
 l.add("C"); 
 Object arr[]=l.toArray(); 
 for(Object a:arr) 
 { 
 String str=(String)a; 
 System.out.println(str); 
 } 
 } 
</code></pre>

for reference, refer this link <a href="http://techno-terminal.blogspot.in/2015/11/how-to-obtain-array-from-arraylist.html" rel="nofollow">http://techno-terminal.blogspot.in/2015/11/how-to-obtain-array-from-arraylist.html</a>

blocks|key|742708|text|一种方法是添加第二个for循环，其中打印在第一个for循环中完成。如下所示：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|742709|static+String[]+SENTENCE;+

public+static+void+main(String+[]args)+throws+Exception{

+++Scanner+sentence+=+new+Scanner(new+File("assets/blah.txt"));
+++ArrayList<String>+sentenceList+=+new+ArrayList<String>();

+++while+(sentence.hasNextLine())
+++{
+++++++sentenceList.add(sentence.nextLine());
+++}

+++sentence.close();

+++String[]+sentenceArray+=+sentenceList.toArray(new+String[sentenceList.size()]);
++//+System.out.println(sentenceArray.length);
+++for+(int+r=0;r<sentenceArray.length;r%2B%2B)
+++{
+++++++SENTENCE+=+sentenceArray[r].split("(?<=[.!?])\\s*");+//split+sentences+and+store+in+array+

+++++++for+(int+i=0;i<SENTENCE.length;i%2B%2B)
+++++++{
+++++++++++System.out.println("Sentence+"+%2B+(i%2B1)+%2B+":+"+%2B+SENTENCE[i]);
+++++++}
+++}++++

}|code-block|syntax|javascript|742710|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|$]]

One approach would be to add the Second for Loop where the printing is being done inside the first for loop. Like this:

<pre><code>static String[] SENTENCE; 

public static void main(String []args) throws Exception{

 Scanner sentence = new Scanner(new File("assets/blah.txt"));
 ArrayList&lt;String&gt; sentenceList = new ArrayList&lt;String&gt;();

 while (sentence.hasNextLine())
 {
 sentenceList.add(sentence.nextLine());
 }

 sentence.close();

 String[] sentenceArray = sentenceList.toArray(new String[sentenceList.size()]);
 // System.out.println(sentenceArray.length);
 for (int r=0;r&lt;sentenceArray.length;r++)
 {
 SENTENCE = sentenceArray[r].split("(?&lt;=[.!?])\\s*"); //split sentences and store in array 

 for (int i=0;i&lt;SENTENCE.length;i++)
 {
 System.out.println("Sentence " + (i+1) + ": " + SENTENCE[i]);
 }
 } 

}
</code></pre>

blocks|key|526240|text|我通常使用这种方法。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|526241|public+static+void+main(String[]+args)+{

++++ArrayList<Integer>+list+=+new+ArrayList<>();
++++list.add(1);
++++list.add(2);
++++list.add(3);

++++int[]+arr+=+list.stream().mapToInt(i+->+i).toArray();

++++System.out.println(Arrays.toString(arr));+//+[1,+2,+3]
}|code-block|syntax|javascript|526242|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|$]]

I usually use this method.
<pre><code>public static void main(String[] args) {

 ArrayList&lt;Integer&gt; list = new ArrayList&lt;&gt;();
 list.add(1);
 list.add(2);
 list.add(3);

 int[] arr = list.stream().mapToInt(i -&gt; i).toArray();

 System.out.println(Arrays.toString(arr)); // [1, 2, 3]
}
</code></pre>

I want to know if it is safe/advisable to convert from ArrayList to Array?
I have a text file with each line a string:

<pre><code>1236
1233
4566
4568
....
</code></pre>

I want to read them into array list and then i convert it to Array. Is it advisable/legal to do that?

thanks

From Arraylist to Array

我想知道从ArrayList转换到数组是否安全/可取？我有一个文本文件，每一行都有一个字符串：1236123345664568....我想将它们读入数组列表，然后将其转换为数组。这样做是明智的/合法的吗？谢谢

问从Arraylist到Array
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