java工具类的使用

一、自定义排序

Collections.sort的两种用法，简单明了 ：

http://blog.csdn.net/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