Arrays.asList(T... a)---的限制

import java.util.Arrays;
import java.util.List;

public class TT {

    public static void main(String[] args) {
        List list = Arrays.asList(12, 13, 14);
        list.add(15);
    }
}

------------

Exception in thread "main" java.lang.UnsupportedOperationException
    at java.util.AbstractList.add(AbstractList.java:148)
    at java.util.AbstractList.add(AbstractList.java:108)
    at TT.main(TT.java:8)

---------------------

Arrays.asList方法返回的List是一个大小固定的数组表示的。

不能add,delete操作。

/**
     * Returns a fixed-size list backed by the specified array.  (Changes to
     * the returned list "write through" to the array.)  This method acts
     * as bridge between array-based and collection-based APIs, in
     * combination with {@link Collection#toArray}.  The returned list is
     * serializable and implements {@link RandomAccess}.
     *
     * <p>This method also provides a convenient way to create a fixed-size
     * list initialized to contain several elements:
     * <pre>
     *     List&lt;String&gt; stooges = Arrays.asList("Larry", "Moe", "Curly");
     * </pre>
     *
     * @param a the array by which the list will be backed
     * @return a list view of the specified array
     */
    public static <T> List<T> asList(T... a) {
    return new ArrayList<T>(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;
        }
    }

---------这个实现中，并没有add,delete方法。

还有一个限制：

import java.util.*;

class Snow {}
class Powder extends Snow {}
class Light extends Powder {}
class Heavy extends Powder {}
class Crusty extends Snow {}
class Slush extends Snow {}

public class AsListInference {
  public static void main(String[] args) {
    List<Snow> snow1 = Arrays.asList(
      new Crusty(), new Slush(), new Powder());

    // Won't compile:
     List<Snow> snow2 = Arrays.asList(
       new Light(), new Heavy());
    // Compiler says:
    // found   : java.util.List<Powder>
    // required: java.util.List<Snow>

    // Collections.addAll() doesn't get confused:
    List<Snow> snow3 = new ArrayList<Snow>();
    Collections.addAll(snow3, new Light(), new Heavy());

    // Give a hint using an
    // explicit type argument specification:
    List<Snow> snow4 = Arrays.<Snow>asList(
       new Light(), new Heavy());
  }
} ///:~