是否有一个实用方法来创建具有指定大小和内容的列表？

发布于 2024-11-10 02:19:52 字数 510 浏览 6 评论 0原文

public static <T> List<T> repeat(T contents, int length) {
    List<T> list = new ArrayList<T>();
    for (int i = 0; i < length; i++) {
        list.add(contents);
    }
    return list;
}

这是我们专有的公共库中的实用方法。它对于创建列表很有用。例如，我可能需要一个包含 68 个问号的列表来生成大型 SQL 查询。这使您可以通过一行代码而不是四行代码来完成此操作。

java/apache-commons 中是否有一个实用程序类已经执行此操作？我浏览了 ListUtils、CollectionUtils、Arrays、Collections，几乎所有我能想到的东西，但我在任何地方都找不到它。如果可能的话，我不喜欢在代码中保留通用实用方法，因为它们对于 apache 库来说通常是多余的。

原文

public static <T> List<T> repeat(T contents, int length) {
    List<T> list = new ArrayList<T>();
    for (int i = 0; i < length; i++) {
        list.add(contents);
    }
    return list;
}

This is a utility method in our proprietary commons libraries. It's useful for creating lists. For example, I might want a list of 68 question marks for generating a large SQL query. This lets you do that in one line of code, instead of four lines of code.

Is there a utility class somewhere in java/apache-commons which already does this? I browsed ListUtils, CollectionUtils, Arrays, Collections, pretty much everything I could think of but I can't find it anywhere. I don't like keeping generic utility methods in my code, if possible, since they're usually redundant with apache libraries.

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攀登最高峰 2024-11-17 02:19:52

Collections 实用程序类将为您提供帮助：

list = Collections.nCopies(length,contents);

或者如果您想要一个可变列表：

list = new ArrayList<T>(Collections.nCopies(length,contents));
           // or whatever List implementation you want.

The Collections utility class will help you:

list = Collections.nCopies(length,contents);

or if you want a mutable list:

list = new ArrayList<T>(Collections.nCopies(length,contents));
           // or whatever List implementation you want.

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奶茶白久 2024-11-17 02:19:52

Google Guava 有以下功能：

newArrayListWithExpectedSize(int estimatedSize)

和：

newArrayList(E... elements)

但你不能两者兼而有之，如果有用的话，也许可以提交一个补丁。更多信息请参见：

http://guava -libraries.googlecode.com/svn/trunk/javadoc/com/google/common/collect/Lists.html

Google Guava has the following:

newArrayListWithExpectedSize(int estimatedSize)

and:

newArrayList(E... elements)

but you can't do both, maybe submit a patch if it's going to be useful. More info here:

http://guava-libraries.googlecode.com/svn/trunk/javadoc/com/google/common/collect/Lists.html

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云之铃。 2024-11-17 02:19:52

怎么样 java.util.Arrays.asList ？

您可以将内容作为 var-arg< 传递/a>：

List<String> planets = Arrays.asList( "Mercury", "Venus", "Earth", "Mars" );

请注意，您也可以传入一个数组：

String[] ps = new String[]{ "Mercury", "Venus", "Earth", "Mars" };
List<String> planets = Arrays.asList( ps );

但它是由数组“支持”的，因为更改数组的内容将反映在列表中：

String[] ps = new String[]{ "Mercury", "Venus", "Earth", "Mars" };
List<String> planets = Arrays.asList( ps );
ps[3] = "Terra";
assert planets.get(3).equals( "Terra" );

How about java.util.Arrays.asList ?

You can just pass in the contents as a var-arg:

List<String> planets = Arrays.asList( "Mercury", "Venus", "Earth", "Mars" );

Mind you, you can pass in an array as well:

String[] ps = new String[]{ "Mercury", "Venus", "Earth", "Mars" };
List<String> planets = Arrays.asList( ps );

but it is "backed" by the array in that changing the contents of the array will be reflected in the list:

String[] ps = new String[]{ "Mercury", "Venus", "Earth", "Mars" };
List<String> planets = Arrays.asList( ps );
ps[3] = "Terra";
assert planets.get(3).equals( "Terra" );

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