make ArrayList只读

Question

在Java中,如何ArrayList在初始化之后创建只读(以便没有人可以添加元素,编辑或删除元素)？

Answer 1

通行证ArrayList进入Collections.unmodifiableList().它返回指定列表的不可修改视图.只使用此返回List,而不是原始ArrayList.

Answer 2

将列表对象传递给Collections.unmodifiableList(). 请参阅下面的示例。

import java.util.*;

public class CollDemo
{
    public static void main(String[] argv) throws Exception
    {
        List stuff = Arrays.asList(new String[] { "a", "b" });
        List list = new ArrayList(stuff);
        list = Collections.unmodifiableList(list);
        Set set = new HashSet(stuff);
        set = Collections.unmodifiableSet(set);
        Map map = new HashMap();
        map = Collections.unmodifiableMap(map);
        System.out.println("Collection is read-only now.");
    }
}