为什么在 java.util.Arrays 中有一个 ArrayList 声明 [英] Why is there an ArrayList declaration within java.util.Arrays
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问题描述
在 JDK 1.7 中,asList
使用了一个 ArrayList
声明.
In JDK 1.7, there is an ArrayList
declaration which is used by asList
.
他们为什么要创建一个新的私有静态类
而不使用java.util.ArrayList
:
Why did they make a new private static class
and not use java.util.ArrayList
:
@SafeVarargs
public static <T> List<T> asList(T... a) {
return new ArrayList<>(a);
}
/**
* @serial include
*/
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) {
if (array==null)
throw new NullPointerException();
a = array;
}
public int size() {
return a.length;
}
public Object[] toArray() {
return a.clone();
}
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;
}
public E get(int index) {
return a[index];
}
public E set(int index, E element) {
E oldValue = a[index];
a[index] = element;
return oldValue;
}
public int indexOf(Object o) {
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;
}
public boolean contains(Object o) {
return indexOf(o) != -1;
}
}
推荐答案
因为Arrays.asList()
由给定的数组支持.它包装了那个数组;对数组的更改反映在 List
中,反之亦然.
Because the List
returned by Arrays.asList()
is backed by the given array. It wraps that array; changes to the array are reflected in the List
and vice versa.
此外,因此,此处返回的 List
具有固定大小.因此,它不能是 ArrayList
,因为 ArrayList
可以增长或缩小.
Also, as a result of this, the List
returned here has a fixed size. So, it can't be an ArrayList
because ArrayList
can grow or shrink.
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