原文鏈接:https://www.cnblogs.com/baby123/p/12619872.html
Arrays.asList與Arrays.stream
java Arrays.asList與Arrays.stream
（1）Arrays.asList
將數組轉化為list
Arrays.asList("a","ab","abc").stream() .filter(s->s.contains("ab")) .map(s->s.toUpperCase()) .forEach(System.out::println);
注：
一旦初始化元素后，集合的size就是不可變的
所以下面的代碼會報錯 java.lang.UnsupportedOperationException
List list = Arrays.asList("a","ab","abc"); list.clear(); list.remove("a"); list.add("g");
Arrays.asList源碼
@SafeVarargs @SuppressWarnings("varargs") public static <T> List<T> asList(T... a) { return new ArrayList<>(a); }
ArrayList
private static class ArrayList<E> extends AbstractList<E>
implements RandomAccess, java.io.Serializable
{
private static final long serialVersionUID = -2764017481108945198L;
private final E[] a;
ArrayList(E[] array) {
a = Objects.requireNonNull(array);
}
@Override
public int size() {
return a.length;
}
@Override
public Object[] toArray() {
return a.clone();
}
@Override
@SuppressWarnings("unchecked")
public <T> T[] toArray(T[] a) {
int size = size();
if (a.length < size)
return Arrays.copyOf(this.a, size,
(Class<? extends T[]>) a.getClass());
System.arraycopy(this.a, 0, a, 0, size);
if (a.length > size)
a[size] = null;
return a;
}
@Override
public E get(int index) {
return a[index];
}
@Override
public E set(int index, E element) {
E oldValue = a[index];
a[index] = element;
return oldValue;
}
@Override
public int indexOf(Object o) {
E[] a = this.a;
if (o == null) {
for (int i = 0; i < a.length; i++)
if (a[i] == null)
return i;
} else {
for (int i = 0; i < a.length; i++)
if (o.equals(a[i]))
return i;
}
return -1;
}
@Override
public boolean contains(Object o) {
return indexOf(o) != -1;
}
@Override
public Spliterator<E> spliterator() {
return Spliterators.spliterator(a, Spliterator.ORDERED);
}
@Override
public void forEach(Consumer<? super E> action) {
Objects.requireNonNull(action);
for (E e : a) {
action.accept(e);
}
}
@Override
public void replaceAll(UnaryOperator<E> operator) {
Objects.requireNonNull(operator);
E[] a = this.a;
for (int i = 0; i < a.length; i++) {
a[i] = operator.apply(a[i]);
}
}
@Override
public void sort(Comparator<? super E> c) {
Arrays.sort(a, c);
}
}
這個內部類沒有add,clear,remove方法
繼續找AbstractList，報錯來自這
public void add(int index, E element) { throw new UnsupportedOperationException(); }public E remove(int index) {
throw new UnsupportedOperationException();
}
可以在外面這樣包一層ArrayList，這樣就可以對數組操作了
List<String> list = new ArrayList<>(Arrays.asList("a", "b", "c")); list.remove("a"); list.add("g"); list.forEach(System.out::println);
（2）Arrays.stream
將數組轉換成流
Arrays.Stream 或 Stream.of 都可以將 Array 轉換為 Stream
Arrays.stream(new String[]{"a","ab","abc"}) .map(s->Arrays.asList(s)) .flatMap(l->l.stream()) .forEach(System.out::println);
Stream.of的源碼
public static<T> Stream<T> of(T... values) { return Arrays.stream(values); }
注：
調用了Arrays.Stream
Arrays.Stream的源碼
public static <T> Stream<T> stream(T[] array) { return stream(array, 0, array.length); }
原始數組
Arrays.Stream
int [] s= new int[]{1, 2, 3}; IntStream s1 = Arrays.stream(s); s1.forEach(System.out::println);
Stream.of
Stream<int[]> s2 = Stream.of(s); IntStream s3 = s2.flatMapToInt(Arrays::stream); s3.forEach(System.out::println);
對於對象數組，都會調用Arrays.stream
對於原始數組，Arrays.stream更方便，它可以直接返回固定大小的IntStream