作_操_合_集

//Collections
List<String> list = new ArrayList<String>();
List lista = Collections.EMPTY_LIST;
Map map = Collections.EMPTY_MAP;
Set set = Collections.EMPTY_SET;
Collections.sort(list);
Arrays.sort(new int[]{1,6,9,2,8,7});
Collections.copy(new ArrayList(), list);
list = Arrays.asList(new String[] {"a", "b"});
list.toArray(new String[list.size()]);

//迭代Map
Map<String,Object> map = new HashMap<String,Object>();
for (Map.Entry<String, Object> entry : map.entrySet())
{
System.out.println(entry.getKey(),entry.getValue());
}

//List去重复
Set set = new HashSet(new ArrayList());
list1.clear();
list1.addAll(set);

//返回交集到list1中,以左边集合为标准
List<String> list1 = new ArrayList<String>();
List<String> list2 = new ArrayList<String>();
list1.retainAll(list2);

//差集--以左边集合为标准，返回右边集合中没有的元素
List<String> list1 = new ArrayList<String>();
List<String> list2 = new ArrayList<String>();
list1.removeAll(list2)；

//并集 -- 将两个集合中的所有元素保存到第一个集合中
List<String> list1 = new ArrayList<String>();
List<String> list2 = new ArrayList<String>();
list1.addAll(list2);
list1.addAll(list2)

=======================================================
    /**
     * 冒泡排序
     * 前后两个元素比较大小
     * @param index
     */
    public static void maoPao(int[] index)
    {
        int center = 0;
        for (int i = 0; i < index.length; i++)
        {
            for (int j = 0; j < index.length - i - 1; j++)
            {
                //降序 “<”  ,  升序  “>”
                if (index[j] < index[j + 1])
                {
                    center = index[j];
                    index[j] = index[j + 1];
                    index[j + 1] = center;
                }
            }
        }
    }
   
    /**
     * 选择排序
     * 每一次循环取出最大值，赋给最后一位
     * @param index
     */
    public static void xuanZe(int[] index)
    {
        int a;
        for (int i = 1; i < index.length; i++)
        {
            a = 0;
            for (int j = 1; j <= index.length - i; j++)
            {
                //升序  “>” ,  降序 “<”
                if (index[j] > index[a])
                {
                    a = j;
                }
            }
            int temp = index[index.length - i];
            index[index.length - i] = index[a];
            index[a] = temp;
        }
    }

/**
     * 插入排序
     * 多个比较一个
     * @param index
     */
    public static void insertIndex(int[] index)
    {
        for (int i = 1; i < index.length; i++)
        {
            for (int j = 0; j < i; j++)
            {
                //升序  “>” ,  降序 “<”
                if (index[j] > index[i])
                {
                    int temp = index[i];
                    index[i] = index[j];
                    index[j] = temp;
                }
            }
        }
    }