Collections類常用方法總結

Collections則是集合類的一個工具類/幫助類，其中提供了一系列靜態方法，用於對集合中元素進行排序、搜索以及線程安全等各種操作。

 

1、    sort(Collection)方法的使用(含義：對集合進行排序)。
       例：對已知集合c進行排序？

            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);
                   }
            }

        運行結果為：[l, o, v, e]
                  [e, l, o, v]         

 

2、   shuffle(Collection)方法的使用(含義：對集合進行隨機排序)。
      例：shuffle(Collection)的簡單示例？

           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);
                        }
             }

            運行結果為：[l, o, v, e]
                      [l, v, e, o]
                      [o, v, e, l]

 

3、 binarySearch(Collection,Object)方法的使用(含義：查找指定集合中的元素，返回所查找元素的索引)。
    例:binarySearch(Collection,Object)的簡單示例？

         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);
                         
                    }
          }

    運行結果為：[l, o, v, e]
               1

 

4、  replaceAll(List list,Object old,Object new)
     方法的使用(含義：替換批定元素為某元素,若要替換的值存在剛返回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);
                    }
          }

    運行結果為：
                [one, two, three, four, five, six, siven]
                true
                [one, two, three, four, five, six, siven eight]

 

5、   reverse()方法的使用(含義：反轉集合中元素的順序)。
      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);
              }
          }

   運行結果為：
             [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(含義：集合中的元素向后移m個位置，在后面被遮蓋的元素循環到前面來)。
       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);
                      }
            }

    運行結果為：
              [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(含義：將集合n中的元素全部復制到m中,並且覆蓋相應索引的元素)。
       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 復制過來的哈".split(" "));
                            System.out.println(n);
                            Collections.copy(m,n);
                            System.out.println(m);
                      }
             }

   運行結果為：[one, two, three, four, five, six, siven]
             [我, 是, 復制過來的哈]
             [我, 是, 復制過來的哈, four, five, six, siven]  

 

8、     swap(List list,int i,int j)方法的使用(含義：交換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);
                        }
             }

    運行結果為：
           [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(含義：用對象o替換集合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);
                  }
       }

     運行結果為：
              [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(含義：返回大小為n的List，List不可改變,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"));
                   }
        }

    運行結果為：
        　　  [嘿嘿, 嘿嘿, 嘿嘿, 嘿嘿, 嘿嘿]