集合框架的工具类----Collections

/*
 *集合框架的工具类
 *Collections
 */

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


public class CollectionsDemo {
	public static void main(String[] args) {
		sortDemo();
		System.out.println();
		binarySearshDemo();
	}
	public static void binarySearshDemo(){
		ArrayList<String> list=new ArrayList<String>();
		list.add("asdas");
		list.add("rtr");
		list.add("hh");
		list.add("hh");
		list.add("aa");
		list.add("asdadcsdfs");
		list.add("ujuku");
		Collections.sort(list);
		sop(list);
		//必须要先排序，才能使用binarySearch方法
		int index=Collections.binarySearch(list, "rtrq");
		int index1=halfSearch(list,"rtrq");
		sop("index:"+index);
		sop("index1:"+index1);
	}
	//binarySearch方法的原理
	public static int halfSearch(ArrayList<String> list,String key){
		int max,min,mid;
		max=list.size()-1;
		min=0;
		while(min<=max)
		{
			mid=(min+max)>>1; //  /2;
			String str=list.get(mid);
			int num=str.compareTo(key);
			if(num>0)
				max=mid-1;
			else if(num<0)
				min=mid+1;
			else
				return mid;
		}
		return -min-1;
	}
	//比较器原理(如果元素自身不具备比较器，就要自定义一个比较器)
	public static int halfSearch2(ArrayList<String> list,String key,Comparator<String> cmp){
		int max,min,mid;
		max=list.size()-1;
		min=0;
		while(min<=max)
		{
			mid=(min+max)>>1; //  /2;
			String str=list.get(mid);
			int num=cmp.compare(str,key);
			if(num>0)
				max=mid-1;
			else if(num<0)
				min=mid+1;
			else
				return mid;
		}
		return -min-1;
	}
	public static void sortDemo(){
		ArrayList<String> list=new ArrayList<String>();
		list.add("asdas");
		list.add("rtr");
		list.add("hh");
		list.add("hh");
		list.add("aa");
		list.add("asdadcsdfs");
		list.add("ujuku");
		sop("排序前：");
		sop(list);
		Collections.sort(list);
		sop("自然排序的结果：");
		sop(list);
		//int index=halfSearch2(list,"aa",new StrLenComparator());
		Collections.sort(list,new StrLenComparator());
		sop("按照长度排序：");
		sop(list);
		//sop(index);
		String valuemax=Collections.max(list);
		sop("valuemax:"+valuemax);
		String lenmax=Collections.max(list,new StrLenComparator());
		sop("Lenmax:"+lenmax);
	}
	public static void sop(Object obj){
		System.out.println(obj);
	}
}
class StrLenComparator implements Comparator<String>{
	@Override
	public int compare(String s1, String s2) {
		// TODO 自动生成的方法存根
		if(s1.length()>s2.length())
			return 1;
		if(s1.length()<s2.length())
			return -1;
		return s1.compareTo(s2);
	}	
}

结果图：