1.Collections 是一个操作 Set、List 和 Map 等集合的工具类;
2.Method:
reverse(List):反转 List 中元素的顺序
shuffle(List):对 List 集合元素进行随机排序
sort(List):根据元素的自然顺序对指定 List 集合元素按升序排序
sort(List,Comparator):根据指定的 Comparator 产生的顺序对 List 集合元素进行排序
swap(List,int, int):将指定 list 集合中的 i 处元素和 j 处元素进行交换
int frequency(Collection,Object):返回指定集合中指定元素的出现次数
void copy(List dest,List src):将src中的内容复制到dest中
boolean replaceAll(List list,Object oldVal,Object newVal):使用新值替换 List 对象的所有旧值
3.e.g.
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public class CollectionsClss {
@Test
public void MM(){
List lt=new ArrayList();
lt.add(23);
lt.add(24);
lt.add(168);
lt.add(188);
lt.add(996);
lt.add(580);
lt.add(574);
lt.add(23);
lt.add(23);
System.out.println(lt);
System.out.println("$$$$$$$$$$$$$$$$$$$$$$$$");
Collections.reverse(lt);
System.out.println(lt);
System.out.println("$$$$$$$$$$$$$$$$$$$$$$$$");
Collections.shuffle(lt);
System.out.println(lt);
System.out.println("$$$$$$$$$$$$$$$$$$$$$$$$");
Collections.sort(lt);
System.out.println(lt);
System.out.println("$$$$$$$$$$$$$$$$$$$$$$$$");
Collections.swap(lt, 0, 4);
System.out.println(lt);
System.out.println("$$$$$$$$$$$$$$$$$$$$$$$$");
System.out.println(Collections.max(lt));
System.out.println(Collections.min(lt));
System.out.println("$$$$$$$$$$$$$$$$$$$$$$$$");
int count=Collections.frequency(lt,23);
System.out.println(count);
System.out.println("$$$$$$$$$$$$$$$$$$$$$$$$");
List ltbb= Arrays.asList(new Object[9]);
Collections.copy(ltbb,lt);
System.out.println(ltbb);
}
}
[23, 24, 168, 188, 996, 580, 574, 23, 23]
$$$$$$$$$$$$$$$$$$$$$$$$
[23, 23, 574, 580, 996, 188, 168, 24, 23]
$$$$$$$$$$$$$$$$$$$$$$$$
[23, 996, 188, 23, 23, 168, 574, 24, 580]
$$$$$$$$$$$$$$$$$$$$$$$$
[23, 23, 23, 24, 168, 188, 574, 580, 996]
$$$$$$$$$$$$$$$$$$$$$$$$
[168, 23, 23, 24, 23, 188, 574, 580, 996]
$$$$$$$$$$$$$$$$$$$$$$$$
996
23
$$$$$$$$$$$$$$$$$$$$$$$$
3
$$$$$$$$$$$$$$$$$$$$$$$$
[168, 23, 23, 24, 23, 188, 574, 580, 996]