java集合

1、map排序

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.TreeMap;
/**
 * 
 * @Description: map排序
 *
 * @author thrillerzw
 * @create time 2014-4-17
 */
public class MapTest {

	public static void main(String[] args) {
		hashMapSort();
	}
	
	/**
	 * 
	 * @Description: hashmap根据值得长度降序排列
	 * 思路：将hashmap转为list，用Collections.sort 配合 比较器对list排序
	 * @author thrillerzw
	 * @create time 2014-4-17
	 */
	static void hashMapSort() {
		Map<String, String> map = new HashMap<String, String>();
		map.put("a", "11");
		map.put("c", "1");
		map.put("b", "111");
		//通过ArrayList构造函数把map.entrySet()转换成list 
		Set<Map.Entry<String, String>> set = map.entrySet();
		List<Map.Entry<String, String>> list = new ArrayList<Map.Entry<String, String>>(set);
		Collections.sort(list, new Comparator<Map.Entry<String, String>>() {
			public int compare(Map.Entry<String, String> o1, Map.Entry<String, String> o2) {
				if (o1.getValue().length() >= o2.getValue().length()) {
					return -1;
				} else {
					return 1;
				}
				//按key排序,字符串compareTo比较   res=1 或者-1  return -res;
				/*int res=o1.getKey().compareTo(o2.getKey());
				return res; */
			}
		});
		//排序后，使用排好序的list
		System.out.println(list);
	}
	/**
	 * 
	 * @Description: TreeMap按照key 降序排列。
	 * @author thrillerzw 
	 * @create time 2014-4-17 上午11:26:47
	 */
	static void treemapKeySort() {
		Map<String, String> map = new TreeMap<String, String>(new Comparator<String>() {
			public int compare(String obj1, String obj2) {
				//降序排序 
				return obj2.compareTo(obj1);
			}
		});
		map.put("b", "h");
		map.put("a", "i");
		map.put("c", "j");
		//输出：map={c=j, b=h, a=i}
		System.out.println("map="+map);
	}
	/**
	 * @Description: treemap按value升序排列
	 * @author thrillerzw 
	 * @create time 2014-4-17
	 */
	static void treemapValsort() {
		List<Map.Entry<String, String>> mappingList = null;
		Map<String, String> map = new TreeMap<String, String>();
		map.put("b", "h");
		map.put("a", "i");
		map.put("c", "j");
		//默认按key升序排序    输出：map={a=bread, b=month, c=attack}
		System.out.println("map="+map);
		//通过ArrayList构造函数把map.entrySet()转换成list 
		mappingList = new ArrayList<Map.Entry<String, String>>(map.entrySet());
		//通过比较器实现比较排序 
		Collections.sort(mappingList, new Comparator<Map.Entry<String, String>>() {
			public int compare(Map.Entry<String, String> mapping1, Map.Entry<String, String> mapping2) {
				return mapping1.getValue().compareTo(mapping2.getValue());
			}
		});
        // 输出：mappingList=[b=h, a=i, c=j]
		System.out.println("mappingList="+mappingList);
	}
	
}

 

2、集合转换

    

//数组转为List
List<String> dataList = Arrays.asList(valArr);
//list转为set
Set<String> tryServers = new HashSet<String>(Arrays.asList(servers));