Java ArrayList 和 HashMap 动态
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/852822/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Java ArrayList and HashMap on-the-fly
提问by Steve M
Can someone please provide an example of creating a Java ArrayListand HashMapon the fly? So instead of doing an add()or put(), actually supplying the seed data for the array/hash at the class instantiation?
可有人请提供创建一个Java的例子ArrayList和HashMap上飞？因此，不是执行add()or put()，而是在类实例化时实际为数组/散列提供种子数据？
To provide an example, something similar to PHP for instance:
举个例子，例如类似于 PHP 的东西：
$array = array (3, 1, 2);
$assoc_array = array( 'key' => 'value' );
采纳答案by bruno conde
List<String> list = new ArrayList<String>() {
{
add("value1");
add("value2");
}
};
Map<String,String> map = new HashMap<String,String>() {
{
put("key1", "value1");
put("key2", "value2");
}
};
回答by Jon Skeet
You mean like this?
你的意思是这样？
public List<String> buildList(String first, String second)
{
List<String> ret = new ArrayList<String>();
ret.add(first);
ret.add(second);
return ret;
}
...
List<String> names = buildList("Jon", "Marc");
Or are you interested in the ArrayListconstructor which takes a Collection<? extends E>? For example:
或者您对ArrayList采用 a的构造函数感兴趣Collection<? extends E>吗？例如：
String[] items = new String[] { "First", "Second", "Third" };
// Here's one way of creating a List...
Collection<String> itemCollection = Arrays.asList(items);
// And here's another
ArrayList<String> itemList = new ArrayList<String>(itemCollection);
回答by Steve McLeod
A nice way of doing this is using Google Collections:
这样做的一个好方法是使用Google Collections：
List<String> list = ImmutableList.of("A", "B", "C");
Map<Integer, String> map = ImmutableMap.of(
1, "A",
2, "B",
3, "C");
回答by cgp
Arrays can be converted to Lists:
数组可以转换为Lists：
List<String> al = Arrays.asList("vote", "for", "me"); //pandering
Note that this does notreturn an ArrayListbut an arbitrary Listinstance (in this case it's an Array.ArrayList)!
请注意，这并没有返回ArrayList指任意的List情况下（在这种情况下，它是一个Array.ArrayList）！
Bruno's approach works best and could be considered on the fly for maps. I prefer the other method for lists though (seen above):
布鲁诺的方法效果最好，可以在地图上即时考虑。我更喜欢列表的其他方法（见上文）：
Map<String,String> map = new HashMap<String,String>() {
{
put("key1", "value1");
put("key2", "value2");
}
};
回答by Yuval Adam
Use a nice anonymous initializer:
使用一个不错的匿名初始化程序：
List<String> list = new ArrayList<String>() {{
add("a");
add("b");
}};
Same goes for a Map:
地图也是如此：
Map<String, String> map = new HashMap<String, String>() {{
put("a", "a");
put("b", "b");
}};
I find this the most elegant and readable.
我觉得这是最优雅和可读的。
Other methods demand creating an array first, then converting it to a List - too expensive in my taste, and less readable.
其他方法需要先创建一个数组，然后将其转换为一个 List - 在我看来太昂贵了，而且可读性较差。
回答by Andreas Petersson
for short lists:
对于短名单：
List<String> ab = Arrays.asList("a","b");
回答by R. Oosterholt
For lists you can use Arrays.asListlike this:
对于列表，您可以像这样使用Arrays.asList：
List<String> stringList = Arrays.asList("one", "two");
List<Integer> intList = Arrays.asList(1, 2);
For Maps you could use this:
对于地图，您可以使用它：
public static <K, V> Map<K, V> mapOf(Object... keyValues) {
Map<K, V> map = new HashMap<>();
K key = null;
for (int index = 0; index < keyValues.length; index++) {
if (index % 2 == 0) {
key = (K)keyValues[index];
}
else {
map.put(key, (V)keyValues[index]);
}
}
return map;
}
Map<Integer, String> map1 = mapOf(1, "value1", 2, "value2");
Map<String, String> map2 = mapOf("key1", "value1", "key2", "value2");
Note: in Java 9you can use Map.of
Note2: Double Brace Initializationfor creating HashMaps as suggested in other answers has it caveats
注意：在Java 9您可以使用Map.of
Note2：Double Brace Initialization按照其他答案中的建议创建 HashMap 时，请注意
