Java 创建具有重复元素的列表
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Creating a list with repeating element
提问by laurt
Is there an utility method in Java that generates a list or array of a specified length with all elements equal to a specified value (e.g ["foo", "foo", "foo", "foo", "foo"])?
Java 中是否有实用方法可以生成指定长度的列表或数组，其中所有元素都等于指定值（例如 ["foo", "foo", "foo", "foo", "foo"]）？
采纳答案by arshajii
You can use Collections.nCopies. Note that this copies the referenceto the given object, not the object itself. If you're working with strings, it won't matter because they're immutable anyway.
您可以使用Collections.nCopies. 请注意，这会复制对给定对象的引用，而不是对象本身。如果您正在处理字符串，那没关系，因为它们无论如何都是不可变的。
List<String> list = Collections.nCopies(5, "foo");
System.out.println(list);
[foo, foo, foo, foo, foo]
回答by René Link
For an array you can use Arrays.fill(Object[] a, Object val)
对于数组，您可以使用Arrays.fill(Object[] a, Object val)
String[] strArray = new String[10];
Arrays.fill(strArray, "foo");
and if you need a list, just use
如果你需要一个列表，只需使用
List<String> asList = Arrays.asList(strArray);
Then I have to use two lines: String[] strArray = new String[5]; Arrays.fill(strArray, "foo");. Is there a one-line solution?
然后我必须使用两行： String[] strArray = new String[5]; Arrays.fill(strArray, "foo");。有单线解决方案吗？
You can use Collections.nCopies(5, "foo")as a one-line solution to get a list :
您可以使用Collections.nCopies(5, "foo")作为单行解决方案来获取列表：
List<String> strArray = Collections.nCopies(5, "foo");
or combine it with toArrayto get an array.
或者将它与它结合起来toArray得到一个数组。
String[] strArray = Collections.nCopies(5, "foo").toArray(new String[5]);
回答by maxpovver
Version you can use for primitive arrays(Java 8):
可用于原始数组的版本（Java 8）：
DoubleStream.generate(() -> 123.42).limit(777).toArray(); // returns array of 777 123.42 double vals
Note that it returns double[], not Double[]
请注意，它返回double[]，而不是Double[]
Works for IntegerStream, DoubleStream, LongStream
适用于 IntegerStream、DoubleStream、LongStream
