java Java数组创建

Java array creation

提问by Matthieu Napoli

This is just a simple question, and I can't find the answer in the documentation !

这只是一个简单的问题，我在文档中找不到答案！

String args[] = new String[0];
args[0] = "test";

Is that correct ? Does this creates an array with 1 element or 0 elements ?

那是对的吗 ？这是否会创建一个包含 1 个元素或 0 个元素的数组？

Thank you, I know, stupid question, but I couldn't find the answer in the Java doc.

谢谢，我知道，愚蠢的问题，但我在 Java 文档中找不到答案。

回答by Gadolin

String[] arr = new String[]{"test"}

String[] arr = new String[]{"test"}

回答by Thirler

This creates an array with length 0. The second line will give an ArrayIndexOutOfBoundsExpection.

这将创建一个长度为 0 的数组。第二行将给出一个ArrayIndexOutOfBoundsExpection.

回答by nanda

Your code is wrong. The first number states the length of the array, so it should be 1

String args[] = new String[1];

你的代码是错误的。第一个数字表示数组的长度，所以它应该是 1

String args[] = new String[1];

The first element in an array is labeled as myArray[0]

数组中的第一个元素标记为 myArray[0]

回答by Matthijs Bierman

If you're trying to do the PHP-like equivalent of args[] = "new entry" then take a look at

如果您正在尝试执行类似 PHP 的 args[] = "new entry" 等效项，请查看

List<String> args = new ArrayList<String>();
args.add("test");
args.add("and some more");
args.add("and even more");

This works fine, and will expand your List automatically. When you need to convert it to an array, you can use:

这很好用，并且会自动扩展您的列表。当需要将其转换为数组时，可以使用：

String[] argArray = args.toArray(new String[args.size()]);

回答by BigMac66

Yep it does seem a little odd - when you create the array you are declaring how many elements the array will have so 0 means no elements. Yet when you traverse an array the first element is the 0th element not the 1st element... Just remember that size/length are not the same as index.

是的，它看起来确实有点奇怪——当你创建数组时，你是在声明数组将有多少个元素，所以 0 意味着没有元素。然而，当你遍历一个数组时，第一个元素是第 0 个元素而不是第一个元素......请记住，大小/长度与索引不同。

回答by sje397

An array of length 5 is created with:

创建长度为 5 的数组：

String myArray[] = new String[5];

The items in this array are indexed using 0, 1, 2, 3, 4 - note that they start at index 0, not index 1, and so go up to (array length - 1).

此数组中的项目使用 0、1、2、3、4 进行索引 - 请注意，它们从索引 0 开始，而不是从索引 1 开始，因此一直到（数组长度 - 1）。

So

所以

new String[0]

creates an array of length 0. Assigning to index 0 will cause an error - there are no positions in the array to assign to.

创建一个长度为 0 的数组。分配给索引 0 将导致错误 - 数组中没有要分配的位置。

new String[1]

would create an array of length 1, with a single position at index 0, so you could then legally do:

将创建一个长度为 1 的数组，在索引 0 处有一个位置，因此您可以合法地执行以下操作：

myArray[0] = "happy days";

回答by Bert F

String args[] = new String[0];

This creates an array with no elements. Accessing any element, even args[0], would cause an ArrayIndexOutOfBoundsException. The number of components of the array is available in args.length.

这将创建一个没有元素的数组。访问任何元素，甚至args[0]，都会导致ArrayIndexOutOfBoundsException. 数组的组件数量在args.length.

String args[] = new String[1];

This creates an array with 1 element. The element is accessed as args[0]. The first element is always at index 0. Accessing any other element would cause an ArrayIndexOutOfBoundsException.

这将创建一个包含 1 个元素的数组。该元素作为 访问args[0]。第一个元素总是在索引 0 处。访问任何其他元素都会导致ArrayIndexOutOfBoundsException.

String args[] = new String[10];

This creates an array with 10 elements. First element is args[0]and the last element is args[9]. The last position is always one less than the size of the array.

这将创建一个包含 10 个元素的数组。第一个元素是args[0]，最后一个元素是args[9]。最后一个位置总是比数组的大小小一个。

References:

参考：

• Java tutorial on arrays: http://download.oracle.com/javase/tutorial/java/nutsandbolts/arrays.html

• Spec: http://java.sun.com/docs/books/jls/second_edition/html/arrays.doc.html

  An array object contains a number of variables. The number of variables may be zero, in which case the array is said to be empty. The variables contained in an array have no names; instead they are referenced by array access expressions that use nonnegative integer index values. These variables are called the components of the array. If an array has n components, we say n is the length of the array; the components of the array are referenced using integer indices from 0 to n - 1, inclusive.

• 关于数组的 Java 教程：http: //download.oracle.com/javase/tutorial/java/nutsandbolts/arrays.html

• 规范：http: //java.sun.com/docs/books/jls/second_edition/html/arrays.doc.html

  一个数组对象包含许多变量。变量的数量可能为零，在这种情况下，数组被称为空。数组中包含的变量没有名称；相反，它们由使用非负整数索引值的数组访问表达式引用。这些变量称为数组的组件。如果一个数组有 n 个分量，我们说 n 是数组的长度；使用从 0 到 n - 1（含）的整数索引来引用数组的组件。

回答by foo

new String[x]will create an empty array of Strings with size x. With x=0, your Array will have noentries, so any attempt to access its elements will result in an exception. If you want it to have oneelement, you should specify you want oneelement: new String[1]will create an Array of Strings with 1 entry.

new String[x]将创建一个大小为 x 的空字符串数组。x=0 时，您的 Array 将没有条目，因此任何访问其元素的尝试都将导致异常。如果你希望它有一个元素，你应该指定你想要一个元素：new String[1]将创建一个包含 1 个条目的字符串数组。

While the above parameter specifies the sizeof the array, the one you use later is the index. In many languages, [] are used for both index (in regular use) and size (when creating arrays), which may be confusing.

虽然上述参数指定了数组的大小，但稍后使用的是index。在许多语言中，[] 用于索引（经常使用）和大小（创建数组时），这可能会造成混淆。

Simple rule: a valid index will always be >= 0, and < size of the array.

简单规则：有效索引总是 >= 0，并且 < 数组的大小。

0 <= index < size

0 <= index < size

An index, also called offset, is how far from the start you go - how many elements into the array you step.

索引，也称为偏移量，是指距您开始的位置有多远 - 您步进的数组中有多少元素。

回答by codaddict

String args[] = new String[0];

String args[] = new String[0];

Creates an array of size 0also called as an emptyarray. Since the array contains no elements, no index can be used on it including 0. Usage of anyindex on it leads to java.lang.ArrayIndexOutOfBoundsException.

创建一个大小的数组，0也称为空数组。由于数组不包含任何元素，因此不能对其使用任何索引，包括0. 在其上使用任何索引都会导致java.lang.ArrayIndexOutOfBoundsException.

回答by easoncxz

here's a simple & official example.

这是一个简单的官方示例。