Collections则是集合类的一个工具类/帮助类,其中提供了一系列静态方法,用于对集合中元素进行排序、搜索以及线程安全等各种操作。

1、    sort(Collection)方法的使用(含义:对集合进行排序)。
       例:对已知集合c进行排序?

            public class Practice {
                   public static void main(String[] args){
                                List c = new ArrayList();
                                c.add("l");
                                c.add("o");
                                c.add("v");
                                c.add("e");
                                System.out.println(c);
                                Collections.sort(c);
                                System.out.println(c);
                   }
            }

        运行结果为:[l, o, v, e]
                  [e, l, o, v]
2、   shuffle(Collection)方法的使用(含义:对集合进行随机排序)。
      例:shuffle(Collection)的简单示例?

           public class Practice {
                     public static void main(String[] args){
                             List c = new ArrayList();
                             c.add("l");
                             c.add("o");
                             c.add("v");
                             c.add("e");
                             System.out.println(c);
                             Collections.shuffle(c);
                             System.out.println(c);
                             Collections.shuffle(c);
                             System.out.println(c);
                        }
             }

            运行结果为:[l, o, v, e]
                      [l, v, e, o]
                      [o, v, e, l]
3、 binarySearch(Collection,Object)方法的使用(含义:查找指定集合中的元素,返回所查找元素的索引)。
    例:binarySearch(Collection,Object)的简单示例?
         public class Practice {
                  public static void main(String[] args){
                          List c = new ArrayList();
                          c.add("l");
                          c.add("o");
                          c.add("v");
                          c.add("e");
                          System.out.println(c);
                          int m = Collections.binarySearch(c, "o");
                          System.out.println(m);
                         
                    }
          }

    运行结果为:[l, o, v, e]
               1
4、  replaceAll(List list,Object old,Object new)     方法的使用(含义:替换批定元素为某元素,若要替换的值存在刚返回true,反之返回false)。
     例:
       public class Practice {
                   public static void main(String[] args){
                          List list = Arrays.asList("one two three four five six siven".split(" "));
                          System.out.println(list);
                          List subList = Arrays.asList("three four five six".split(" "));
                          System.out.println(Collections.replaceAll(list, "siven", "siven eight"));
                          System.out.println(list);
                    }
          }

    运行结果为:
                [one, two, three, four, five, six, siven]
                true
                [one, two, three, four, five, six, siven eight]
5、   reverse()方法的使用(含义:反转集合中元素的顺序)。
      例:
         public class Practice {
             public static void main(String[] args){
                    List list = Arrays.asList("one two three four five six siven".split(" "));
                    System.out.println(list);
                    Collections.reverse(list);
                    System.out.println(list);
              }
          }

   运行结果为:
             [one, two, three, four, five, six, siven]
             [siven, six, five, four, three, two, one]
6、    rotate(List list,int m)方法的使用(含义:集合中的元素向后移m个位置,在后面被遮盖的元素循环到前面来)。
       例:
          public class Practice {
                   public static void main(String[] args){
                            List list = Arrays.asList("one two three four five six siven".split(" "));
                            System.out.println(list);
                            Collections.rotate(list, 1);
                            System.out.println(list);
                      }
            }
    运行结果为:
              [one, two, three, four, five, six, siven]
              [siven, one, two, three, four, five, six]
7、    copy(List m,List n)方法的使用(含义:将集合n中的元素全部复制到m中,并且覆盖相应索引的元素)。
       例:
            public class Practice {
                    public static void main(String[] args){
                            List m = Arrays.asList("one two three four five six siven".split(" "));
                            System.out.println(m);
                            List n = Arrays.asList("我 是 复制过来的哈".split(" "));
                            System.out.println(n);
                            Collections.copy(m,n);
                            System.out.println(m);
                      }
             }
   运行结果为:[one, two, three, four, five, six, siven]
             [我, 是, 复制过来的哈]
             [我, 是, 复制过来的哈, four, five, six, siven]
8、     swap(List list,int i,int j)方法的使用(含义:交换集合中指定元素索引的位置)。
        例:
            public class Practice {
                      public static void main(String[] args){
                             List m = Arrays.asList("one two three four five six siven".split(" "));
                             System.out.println(m);
                             Collections.swap(m, 2, 3);
                             System.out.println(m);
                        }
             }

    运行结果为:
           [one, two, three, four, five, six, siven]
           [one, two, four, three, five, six, siven]
9、 fill(List list,Object o)方法的使用(含义:用对象o替换集合list中的所有元素)。
    例:
       public class Practice {
                 public static void main(String[] args){
                            List m = Arrays.asList("one two three four five six siven".split(" "));
                         System.out.println(m);
                          Collections.fill(m, "啊啊啊");
                         System.out.println(m);
                  }
       }
     运行结果为:
              [one, two, three, four, five, six, siven]
              [啊啊啊, 啊啊啊, 啊啊啊,啊啊啊, 啊啊啊, 啊啊啊, 啊啊啊]
10、 nCopies(int n,Object o)方法的使用(含义:返回大小为n的List,List不可改变,其中的所有引用都指向o)。
     例:
       public class Practice {
                public static void main(String[] args){
                          System.out.println(Collections.nCopies(5, "嘿嘿"));
                   }
        }
    运行结果为:
            [嘿嘿, 嘿嘿, 嘿嘿, 嘿嘿, 嘿嘿]
11、addAll(Collection,T)方法的使用(含义:将所有指定元素添加到指定 collection 中。)
        例:
            public class Practice{
                            public static void main (String[] args){
                                            ArrayList<String> a = new ArrayList();
                                            Collections.addAll(a, "小白","小王","小黑","张三");
                                            System.out.println(a);
                            }
            }
        运行结果为:
                                    [小白, 小王, 小黑, 张三]