java:List包装器,其中允许使用get()/ set()但不添加/删除

Question

我需要List<T>用一些允许调用set/get但不允许添加/删除调用的类来包装,以便列表保持"固定"长度.我认为我有一个薄的包装类(下面)可以工作,但我不是100%正面.

我错过了什么明显的事吗？

import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;

class RestrictedListWrapper<T> implements List<T>
{
    static <T> T fail() throws UnsupportedOperationException
    {
        throw new UnsupportedOperationException();
    }   

    static private class IteratorWrapper<T> implements ListIterator<T>
    {
        final private ListIterator<T> iter;

        private IteratorWrapper(ListIterator<T> iter) { this.iter = iter; }
        static public <T> RestrictedListWrapper.IteratorWrapper<T> wrap(ListIterator<T> target) { 
            return new RestrictedListWrapper.IteratorWrapper<T>(target); 
        }
        @Override public void add(T e) { fail(); }
        @Override public boolean hasNext() { return this.iter.hasNext(); }
        @Override public boolean hasPrevious() { return this.iter.hasPrevious(); }
        @Override public T next() { return this.iter.next(); }
        @Override public int nextIndex() { return this.iter.nextIndex(); }
        @Override public T previous() { return this.iter.previous(); }
        @Override public int previousIndex() { return this.iter.previousIndex(); }
        @Override public void remove() { fail(); }
        @Override public void set(T e) { this.iter.set(e); }
    }       

    final private List<T> list;

    private RestrictedListWrapper(List<T> list) {
        this.list = list;
    }
    static public <T> RestrictedListWrapper<T> wrap(List<T> target) {
        return new RestrictedListWrapper<T>(target);
    }
    @Override public boolean add(T arg0) { return fail();  } 
    @Override public void add(int index, T element) { fail(); }
    @Override public boolean addAll(Collection<? extends T> arg0) {
        return fail(); 
    }
    @Override public boolean addAll(int arg0, Collection<? extends T> arg1) {
        return fail();
    }

    /**
     * clear() allows setting all members of the list to null
     */
    @Override public void clear() {
        ListIterator<T> it = this.list.listIterator();

        while (it.hasNext())
        {
            it.set(null);
            it.next();
        }
    }
    @Override public boolean contains(Object o) {
        return this.list.contains(o);
    }
    @Override public boolean containsAll(Collection<?> c) {
        return this.list.containsAll(c);
    }
    @Override public T get(int index) { return this.list.get(index); }
    @Override public int indexOf(Object o) { return this.list.indexOf(o); }
    @Override public boolean isEmpty() { return false; }
    @Override public Iterator<T> iterator() { 
        return listIterator();
    }
    @Override public int lastIndexOf(Object o) { return this.list.lastIndexOf(o); }
    @Override public ListIterator<T> listIterator() {
        return IteratorWrapper.wrap(this.list.listIterator());
    }
    @Override public ListIterator<T> listIterator(int index) {
        return IteratorWrapper.wrap(this.list.listIterator(index));
    }
    @Override public boolean remove(Object o) { return fail(); }
    @Override public T remove(int index) { fail(); return fail(); }
    @Override public boolean removeAll(Collection<?> c) { return fail(); }
    @Override public boolean retainAll(Collection<?> c) { return fail(); }

    @Override public T set(int index, T element) { return this.list.set(index, element); }
    @Override public int size() { return this.list.size(); }
    @Override public List<T> subList(int fromIndex, int toIndex) {
        return new RestrictedListWrapper<T>(this.list.subList(fromIndex, toIndex));
    }
    @Override public Object[] toArray() { return this.list.toArray(); }
    @Override public <T> T[] toArray(T[] a) { return this.list.toArray(a); }
}

Answer 1

Apache Commons Collections有一个FixedSizedList类就是这样做的.

装饰另一个List以修复阻止添加/删除的大小.

不支持添加,删除,清除和保留操作.允许使用set方法(因为它不会更改列表大小).

LarvaLabs提供了java5-generics友好版本.