:

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).

试试这个:

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

Object[] ol = list.toArray();

我认为这是最简单的方法:

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

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.

Java 8中的替代方案:

String[] strings = list.stream().toArray(String[]::new);

从Java 11开始:

String[] strings = list.toArray(String[]::new);

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);

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

我遇到了这个代码片段来解决这个问题。

//Creating a sample ArrayList 
List<Long> list = new ArrayList<Long>();

//Adding some long type values
list.add(100l);
list.add(200l);
list.add(300l);

//Converting the ArrayList to a Long
Long[] array = (Long[]) list.toArray(new Long[list.size()]);

//Printing the results
System.out.println(array[0] + " " + array[1] + " " + array[2]);

转换过程如下:

它创建了一个新的Long数组，其大小与原始列表相同 它将原始的ArrayList转换为使用新创建的数组 它将该数组转换为长数组(Long[])，我将其适当地命名为'array'

你可以像下面这样使用toArray() api:

ArrayList<String> stringList = new ArrayList<String>();
stringList.add("ListItem1");
stringList.add("ListItem2");
String[] stringArray = new String[stringList.size()];
stringArray = stringList.toArray(stringList);

数组中的值为:

for(String value : stringList)
{
    System.out.println(value);
}

这是可行的。种。

public static Object[] toArray(List<?> a) {
    Object[] arr = new Object[a.size()];
    for (int i = 0; i < a.size(); i++)
        arr[i] = a.get(i);
    return arr;
}

然后是主要方法。

public static void main(String[] args) {
    List<String> list = new ArrayList<String>() {{
        add("hello");
        add("world");
    }};
    Object[] arr = toArray(list);
    System.out.println(arr[0]);
}

在没有Java 8的情况下，我想到的最好的事情是:

public static <T> T[] toArray(List<T> list, Class<T> objectClass) {
    if (list == null) {
        return null;
    }

    T[] listAsArray = (T[]) Array.newInstance(objectClass, list.size());
    list.toArray(listAsArray);
    return listAsArray;
}

如果有人有更好的方法，请分享:)