java工具类的使用

2019独角兽企业重金招聘Python工程师标准>>>

一、自定义排序

Collections.sort的两种用法，简单明了 ：

http://blog.youkuaiyun.com/janronehoo/article/details/8746447

http://www.cnblogs.com/liuyuanyuanGOGO/p/java_collections.html

Collections.sort(station,(a,b)->{
                return a.getStationNo() - b.getStationNo();
            });

Collections.sort(names, (String a, String b) -> {

    return b.compareTo(a);

});

Java8：Lambda表达式增强版Comparator和排序:

http://www.importnew.com/15259.html

1、数组排序：

		String[] players = {"d","a","c","b"};
		
		System.out.print("排序前: ");
		for(String s : players){
			System.out.print(s.concat(" "));//排序前，players: d a c b
		}
		
//		Arrays.sort(players, new Comparator<String>() {  
//		    @Override  
//		    public int compare(String s1, String s2) {  
//		        return (s1.compareTo(s2));  
//		    }  
//		}); 
		
		Arrays.sort(players, (String s1, String s2) -> (s1.compareTo(s2)));//jdk1.8
		
		System.out.println();
		System.out.print("排序后: ");
		
		for(String s : players){
			System.out.print(s.concat(" "));//排序后，players: a b c d
		}

2、集合排序：

		List<String> players = new ArrayList<>();
		players.add("d");
		players.add("c");
		players.add("a");
		players.add("b");
		
		System.out.println("排序前: " + players);//排序前，players: d c a b
		
//		Collections.sort(players, new Comparator<String>() {  
//		    @Override  
//		    public int compare(String s1, String s2) {  
//		        return (s1.compareTo(s2));  
//		    }  
//		}); 
		
		Collections.sort(players, (String s1, String s2) -> (s1.compareTo(s2)));//jdk1.8
		
		System.out.println("排序后: " + players);//排序后，players: a b c d

		List<String> players = new ArrayList<>();
		players.add("4");
		players.add("3");
		players.add("1");
		players.add("2");
		
		System.out.println("排序前: " + players);//排序前，players: d c a b
		
		//Collections.sort(players, new Comparator<String>() {  
		    //@Override  
		   // public int compare(String s1, String s2) {  
		     //   return (s1.compareTo(s2));  
		    //}  
		//}); 
		
		//Collections.sort(players, (String s1, String s2) -> (s1.compareTo(s2)));//jdk1.8
		
		//Collections.sort(players, (String s1, String s2) -> ( Integer.valueOf(s2) - Integer.valueOf(s1)));//jdk1.8
		
		players.sort((String s1, String s2) -> ( Integer.valueOf(s2) - Integer.valueOf(s1)));//jdk1.8
		
		System.out.println("排序后: " + players);//排序后，players: a b c d

二、数组与List相互转换

1、List转数组：

        List<String> players = new ArrayList<>();
		players.add("d");
		players.add("c");
		players.add("a");
		players.add("b");
		
		//String[] ss = (String[])players.toArray(new String[0]);
		String[] ss = players.toArray(new String[players.size()]);
		
		System.out.print("转换后: ");
		for(String s : ss){
			System.out.print(s.concat(" "));//转换后，ss: d c a b
		}

2、数组转List：

        String[] ss = {"d","c","a","b"};
		
		System.out.print("转换前: ");
		for(String s : ss){
			System.out.print(s.concat(" "));//转换前，ss: d c a b
		}
		
		System.out.println();
		
		List<String> players = Arrays.asList(ss);
		System.out.println("转换后: " + players);//转换后，players: d c a b

 

转载于:https://my.oschina.net/Howard2016/blog/813730