Java：遍历列表列表？
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Java: iterating through list of lists?
提问by hhh
The question but in C#.So does Java have C#'s command? I need it for Matches-SearchTerm-Files-relationship.
问题，但在 C# 中。那么Java有C#的命令吗？我需要它来匹配匹配-搜索词-文件-关系。
foreach(var i in BunchOfItems.SelectMany(k => k.Items)) {}
[Why not for-loops?]I have done such structures in nested for loops but they soon become bloated. So I prefer something more succint like the above.
[为什么不用 for 循环？]我在嵌套的 for 循环中做过这样的结构，但它们很快就会变得臃肿。所以我更喜欢像上面那样更简洁的东西。
public static Stack<Integer[]> getPrintPoss(String s,File f,Integer maxViewPerF)
{
Stack<File> possPrint = new Stack<File>();
Integer[] poss = new Integer[4]();
int u,size;
for(File f:files)
{
size = f2S(f).length();
u = Math.min(maxViewsPerF,size);
for(int i=0; i<u;i++)
{
// Do something --- bloated, and soon out of control
// wants more succintly
}
}
return possPrint;
}
采纳答案by BalusC
回答by someguy
for (List<Object> lo : list) {
for (Object o : lo) {
// etc etc
}
}
I don't think there's a simpler solution.
我认为没有更简单的解决方案。
回答by bruno conde
I have my own version. Waiting desperately for Closuresin Java :
我有我自己的版本。拼命等待Java 中的闭包：
public static <T, E> Iterable<T> transformMany(Iterable<E> iterable, Func<E, Iterable<T>> f) {
if (null == iterable)
throw new IllegalArgumentException("null iterable");
if (null == f)
throw new IllegalArgumentException("null f");
return new TransformManyIterable<E, T>(iterable, f);
}
public interface Func<E, T> {
T execute(E e);
}
public class TransformManyIterable<TOriginal, TResult> implements Iterable<TResult> {
private Iterable<TOriginal> iterable;
private Func<TOriginal, Iterable<TResult>> func;
public TransformManyIterable(Iterable<TOriginal> iterable,
Func<TOriginal, Iterable<TResult>> func) {
super();
this.iterable = iterable;
this.func = func;
}
class TransformIterator implements Iterator<TResult> {
private Iterator<TOriginal> iterator;
private Iterator<TResult> currentIterator;
public TransformIterator() {
iterator = iterable.iterator();
}
@Override
public boolean hasNext() {
if (currentIterator != null && currentIterator.hasNext())
return true;
else {
while (iterator.hasNext()) {
Iterable<TResult> iterable = func.execute(iterator.next());
if (iterable == null)
continue;
currentIterator = iterable.iterator();
if (currentIterator.hasNext())
return true;
}
}
return false;
}
@Override
public TResult next() {
if (currentIterator != null && currentIterator.hasNext())
return currentIterator.next();
else {
while (iterator.hasNext()) {
Iterable<TResult> iterable = func.execute(iterator.next());
if (iterable == null)
continue;
currentIterator = iterable.iterator();
if (currentIterator.hasNext())
return currentIterator.next();
}
}
throw new NoSuchElementException();
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
}
@Override
public Iterator<TResult> iterator() {
return new TransformIterator();
}
}
Usage:
用法：
Iterable<SomeType> result = transformMany(input, new Func<InputType, Iterable<SomeType>>() {
@Override
public Iterable<SomeType> execute(InputType e) {
return new ArrayList<SomeType>();
}
});
回答by Robin
The SelectMany method is part of LINQ which is .Net-specific. This questionasks about a LINQ equilvalent for java. Unfortunately, it doesn't look like there is a direct equivalent.
SelectMany 方法是特定于 .Net 的 LINQ 的一部分。这个问题询问了 java 的 LINQ 等价物。不幸的是，看起来没有直接的等价物。
回答by Kevin Bourrillion
If you can get the data into an Iterable<Iterable<T>>, then you can get from that to a flattened Iterable<T>using Guava's Iterables.concatmethod. If what you have is really an Iterable<S>, with some way to get from an Sto an Iterable<T>, well, then you have to first use Iterables.transformto view that as the Iterable<Iterable<T>>needed by concat.
如果您可以将数据放入 . Iterable<Iterable<T>>，那么您可以Iterable<T>使用 Guava 的Iterables.concat方法从该数据中获得扁平化。如果你有什么是真正的Iterable<S>，以某种方式从获取S到的Iterable<T>，好了，那么你必须先用Iterables.transform要查看的Iterable<Iterable<T>>需要的concat。
All this will look a lot nicer if and when Java has something resembling closures, but at least today it's possible.
如果 Java 有类似闭包的东西，所有这些看起来都会好很多，但至少在今天这是可能的。
回答by Kyle Krull
With Java 8, you can say
使用 Java 8，你可以说
Collection bunchOfItems = ...;
bunchOfItems.stream().flatMap(k::getItems).forEach(i -> /* operate on i */);
or
或者
Item[] bunchOfItems = ...;
Stream.of(bunchOfItems).flatMap(k::getItems).forEach(i -> /* operate on i */);
depending upon whether you have a Collectionor an Array.
这取决于你是否有一个Collection或一个Array。
