集合之二

排序：Collections.sort()
（1）自然排寻(natural ordering )；
（2）实现比较器(Comparator)接口。
取最大和最小的元素：Collections.max()、Collections.min()。
在已排序的List中搜索指定的元素：Collectons.binarySearch()。

 

import  java.util. * ;
public   class   ArrayListTest1
... {
          public static void printElements(Collection c)
          ...{
                    Iterator it=c.iterator();
                                while(it.hasNext())
                                ...{
                                       System.out.println(it.next());
                                }
          }
                public static void main(String[] args)
                ...{
                                ArrayList al=new ArrayList();
                                al.add(new Student(2,"wanhhu"));
                                al.add(new Student(3,"huaihua"));
                                al.add(new Student(4,"liming"));
                                al.add(new Student(5,"zhanghu"));
                                printElements(al);
                                Collections.sort(al,new Student.StudentComparator());
                                printElements(al);
                                Collections.sort(al,Collections.reverseOrder());//new Student.StudentComparator());
                    printElements(al);
                }
}
class  Student  implements  Comparable
... {
          int num;
          String  name;
          static class StudentComparator implements Comparator
           ...{
            public int compare(Object o1,Object o2)
            ...{
                      Student s1=(Student)o1;
                              Student s2=(Student)o2;
                              int     result=s1.num > s2.num ? 1 : (s1.num==s2.num ? 0 : -1);
                              if(result==0)
                                ...{
                                          result=s1.name.compareTo(s2.name);
                                }
                                        return result;
                }
    }
          Student(int num,String name)
          ...{
                   this.num=num;
                   this.name=name;
          }
          public int compareTo(Object o)
          ...{
                   Student s=(Student)o;
                   return num>s.num ? 1  : (num==s.num ? 0 : -1);
          }
          public String toString()
          ...{
                   return "num="+num+","+"name="+name;
          }
}