java-Collections的应用

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Collection和Collections的区别：

Collection是JAVA集合框架中的顶层接口.常用的两个子接口为：Set和List.

Collections是Java集合框架中操作集合的工具类，所有的方法都是静态的.提供了对List进行排序的功能，也提供了将线程不安全的转为线程安全的方法.

import java.util.*;
class CollectionsDemo
{
public static void main(String[] args)
{
  ArrayList<String>al = new ArrayList<String>();
  al.add("zdd");
  al.add("ad");
  al.add("qsdw");
  al.add("vwerre");
  al.add("sxsd");

  System.out.println("***按照自然顺序***");
  String max =Collections.max(al);
  String min =Collections.min(al);
  System.out.println("max="+max+";min="+min);

  System.out.println("***按照字符长度***");
  String max1 =Collections.max(al, new MyComparator());
  String min1 =Collections.min(al, new MyComparator());
  System.out.println("max="+max1+";min="+min1);

  Collections.sort(al);

System.out.println(al.toString());
toMyString(al );

int num =Collections.binarySearch(al, "qsdw");
System.out.println(num);

       Collections.sort(al, new MyComparator());
  System.out.println(al.toString());
  int num1 = myBinarySearch(al,"qsdw", new MyComparator());
  System.out.println(num1);
}
public static voidtoMyString(ArrayList<String>al)
{
  StringBuilder sb = newStringBuilder();
  sb.append("[");
  for (Iterator it =al.iterator(); it.hasNext(); )
  {
   sb.append(it.next()+ ", ");
  }
  //sb.deleteCharAt(sb.length() -2);
  sb.delete(sb.length()-2,sb.length());
  sb.append("]");
  System.out.println(sb);
}

public static int myBinarySearch(List<String> l, String key,Comparator<String> comp)
{
  int max,min,mid;
  max = l.size() - 1;
  min =0;
  while (min <=max)
  {
   mid = (max +min)/2;
   int num =comp.compare(key, l.get(mid)); //按照自定义比较器比较
   if (num> 0)
    min= mid + 1;
   else if (num< 0)
    max= mid - 1;
   else
    returnmid;
  }
  return -1;
}

}

class MyComparator implements Comparator<String>
{
public int compare(String str1, Stringstr2)
{
  if (str1.length()> str2.length())
   return1;
  else if (str1.length()< str2.length())
   return-1;
  else
   returnstr1.compareTo(str2);
}
}