freezablelist.java

java1.6众多例子参考

/*
 * @(#)FreezableList.java	1.14 05/11/17
 *
 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package com.sun.corba.se.impl.ior ;

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

import com.sun.corba.se.spi.ior.MakeImmutable ;

/** Simple class that delegates all List operations to 
* another list.  It also can be frozen, which means that
* a number of operations can be performed on the list,
* and then the list can be made immutable, so that no
* further changes are possible.  A FreezableList is frozen
* using the makeImmutable method.
*/
public class FreezableList extends AbstractList {
    private List delegate = null ;
    private boolean immutable = false ;

    public boolean equals( Object obj )
    {
	if (obj == null)
	    return false ;

	if (!(obj instanceof FreezableList))
	    return false ;

	FreezableList other = (FreezableList)obj ;

	return delegate.equals( other.delegate ) &&
	    (immutable == other.immutable) ;
    }

    public int hashCode()
    {
	return delegate.hashCode() ;
    }

    public FreezableList( List delegate, boolean immutable  )
    {
	this.delegate = delegate ;
	this.immutable = immutable ;
    }

    public FreezableList( List delegate )
    {
	this( delegate, false ) ;
    }

    public void makeImmutable()
    {
	immutable = true ;
    }

    public boolean isImmutable()
    {
	return immutable ;
    }

    public void makeElementsImmutable()
    {
	Iterator iter = iterator() ;
	while (iter.hasNext()) {
	    Object obj = iter.next() ;
	    if (obj instanceof MakeImmutable) {
		MakeImmutable element = (MakeImmutable)obj ;
		element.makeImmutable() ;
	    }
	}
    }

    // Methods overridden from AbstractList

    public int size()
    {
	return delegate.size() ;
    }

    public Object get(int index)
    {
	return delegate.get(index) ;
    }

    public Object set(int index, Object element)
    {
	if (immutable)
	    throw new UnsupportedOperationException() ;

	return delegate.set(index, element) ;
    }

    public void add(int index, Object element)
    {
	if (immutable)
	    throw new UnsupportedOperationException() ;

	delegate.add(index, element) ;
    }

    public Object remove(int index)
    {
	if (immutable)
	    throw new UnsupportedOperationException() ;

	return delegate.remove(index) ;
    }

    // We also override subList so that the result is a FreezableList.
    public List subList(int fromIndex, int toIndex)
    {
	List list = delegate.subList(fromIndex, toIndex) ;
	List result = new FreezableList( list, immutable ) ;
	return result ;
    }
}