以下(Ondrej的回答):

Foo[] array = list.toArray(new Foo[0]);

Is the most common idiom I see. Those who are suggesting that you use the actual list size instead of "0" are misunderstanding what's happening here. The toArray call does not care about the size or contents of the given array - it only needs its type. It would have been better if it took an actual Type in which case "Foo.class" would have been a lot clearer. Yes, this idiom generates a dummy object, but including the list size just means that you generate a larger dummy object. Again, the object is not used in any way; it's only the type that's needed.

试试这个:

List list = new ArrayList();
list.add("Apple");
list.add("Banana");

Object[] ol = list.toArray();

:

Foo[] array = list.toArray(new Foo[0]);

or:

Foo[] array = new Foo[list.size()];
list.toArray(array); // fill the array

注意，这仅适用于引用类型的数组。对于基元类型数组，使用传统方法:

List<Integer> list = ...;
int[] array = new int[list.size()];
for(int i = 0; i < list.size(); i++) array[i] = list.get(i);

更新:

现在建议使用list。toArray(新的Foo[0]);，不是列表。toArray(新Foo [list.size());。

来自JetBrains Intellij Idea的检测:

There are two styles to convert a collection to an array: either using a pre-sized array (like c.toArray(new String[c.size()])) or using an empty array (like c.toArray(new String[0]). In older Java versions using pre-sized array was recommended, as the reflection call which is necessary to create an array of proper size was quite slow. However since late updates of OpenJDK 6 this call was intrinsified, making the performance of the empty array version the same and sometimes even better, compared to the pre-sized version. Also passing pre-sized array is dangerous for a concurrent or synchronized collection as a data race is possible between the size and toArray call which may result in extra nulls at the end of the array, if the collection was concurrently shrunk during the operation. This inspection allows to follow the uniform style: either using an empty array (which is recommended in modern Java) or using a pre-sized array (which might be faster in older Java versions or non-HotSpot based JVMs).

以下(Ondrej的回答):

Foo[] array = list.toArray(new Foo[0]);

Is the most common idiom I see. Those who are suggesting that you use the actual list size instead of "0" are misunderstanding what's happening here. The toArray call does not care about the size or contents of the given array - it only needs its type. It would have been better if it took an actual Type in which case "Foo.class" would have been a lot clearer. Yes, this idiom generates a dummy object, but including the list size just means that you generate a larger dummy object. Again, the object is not used in any way; it's only the type that's needed.

示例取自此页:http://www.java-examples.com/copy-all-elements-java-arraylist-object-array-example

import java.util.ArrayList;

public class CopyElementsOfArrayListToArrayExample {

  public static void main(String[] args) {
    //create an ArrayList object
    ArrayList arrayList = new ArrayList();

    //Add elements to ArrayList
    arrayList.add("1");
    arrayList.add("2");
    arrayList.add("3");
    arrayList.add("4");
    arrayList.add("5");

    /*
      To copy all elements of java ArrayList object into array use
      Object[] toArray() method.
    */

    Object[] objArray = arrayList.toArray();

    //display contents of Object array
    System.out.println("ArrayList elements are copied into an Array.
                                                  Now Array Contains..");
    for(int index=0; index < objArray.length ; index++)
      System.out.println(objArray[index]);
  }
}

/*
Output would be
ArrayList elements are copied into an Array. Now Array Contains..
1
2
3
4
5

对于ArrayList，以下工作:

ArrayList<Foo> list = new ArrayList<Foo>();

//... add values

Foo[] resultArray = new Foo[list.size()];
resultArray = list.toArray(resultArray);