Collections工具类:提供了关于集合的常用操作

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class CollectionsTest {

/**
* Collections工具类:提供了关于集合的常用操作
*/
public static void main(String[] args) {
ArrayList<String> al = new ArrayList<String>();
al.add("ab");
al.add("aadc");
al.add("aaa");
al.add("hgdfakjg");
al.add("xhyns");
al.add("yyiouop");
al.add("qq");
al.add("zdff");

Collections.sort(al, new StringComparator());

//int pos = Collections.binarySearch(al, "xhyns", new StringComparator());
int pos = MyCollections.binarySearch(al, "zz", new StringComparator());

for(String s : al)
System.out.println(s);

System.out.println("位置:" + pos);
}

}

class StringComparator implements Comparator<String> {
public int compare(String s1, String s2) {
int num = s1.length() - s2.length();
if(num!=0)
return num;
return s1.compareTo(s2);
}
}

class MyCollections {
private MyCollections(){}
public static <T> int binarySearch(List<T> l, T key, Comparator<T> com) {
int min = 0;
int max = l.size()-1;
int mid = 0;
while(max>=min) {
mid = (min+max)/2;
if(com.compare(key,l.get(mid))>0)
min = mid + 1;
else if(com.compare(key,l.get(mid))<0)
max = mid - 1;
else
return mid;
}
//判断mid位置的元素和key的大小
if(com.compare(key, l.get(mid))>0)
return -mid-2;
return -mid-1;
}
}