The java.util.Arrays provide convenient way to create a fixed-size list initialized to contain several elements:
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; } }
List list = Arrays.asList("Larry", "Moe", "Curly");
It seems we get the the instance of ArrayList which inherits AbstractList. But it dones't override the method of add, remove..., etc. As a result, below code will throw exception
public static void main(String[] args) { List list = Arrays.asList("Larry", "Moe", "Curly"); /// list.add("Peter"); list.remove(0); }The result is:
Exception in thread "main" java.lang.UnsupportedOperationException at java.util.AbstractList.remove(AbstractList.java:144) at ArraysTest.main(ArraysTest.java:11)By looking at the source code you will find the cause