TreeMap 排序

最新推荐文章于 2022-08-11 16:57:08 发布

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比较函数类TComp比较两个包含姓和名的字符串。它首先比较姓，具体是这样做的，首先寻找每一个字符串中最后一个空格的下标，然后比较从这个位置开始的每一个元素的子字符串。当两个字符串中姓完全相等时，再比较两个名。这样就形成了先按姓排序，在姓相同的情况下再按名字进行排序的树型映射。

//Use a comparator to sort accounts by last name.
import java.util.*;
//Compare last whole words in two strings.
class TComp implements Comparator{
public int compare(Object a,Object b){
int i,j,k;
String strA,strB;

strA = (String)a;
strB = (String)b;

  //find index of beginning of last name
  i = strA.lastIndexOf(' ');
  j = strB.lastIndexOf(' ');
  k = strA.substring(i).compareTo(strB.substring(j));
  if(k==0) //last name match,check entire name
   return strA.compareTo(strB);
  else
   return k;
}
//no need to override equals
}
public class TreeMapDemo2{
public static void main(String[] args)
{
  //Create a tree map.
  TreeMap tm = new TreeMap(new TComp());

  //Put elements to the map.
  tm.put("Sue Yuan",new Double(17.15));
  tm.put("Jiahui Sheng",new Double(78777));
  tm.put("Huajiang Chen",new Double(12345.77));
  tm.put("Magic Ya",new Double(-99.10));
  tm.put("Quanbing Chen",new Double(100.00));

//Get a set of the entries.
Set set = tm.entrySet();

//Get an iterator.
Iterator i = set.iterator();

  //Display elements.
  while(i.hasNext()){
   Map.Entry me = (Map.Entry)i.next();
   System.out.println(me.getKey() + ": ");
   System.out.println(me.getValue());
  }
  System.out.println();

  //Deposit 1000 into Jiahui Sheng's account
  double balance = ((Double)tm.get("Jiahui Sheng")).doubleValue();
  tm.put("Jiahui Sheng",new Double(balance + 1000));
  System.out.println("Jiahui Sheng's new balance : " + tm.get("Jiahui Sheng"));
}
}