What I want to do is when I have a list of strings " insert "," create "," drop "`` `, I want to sort them in my favorite order instead of the natural order. Specifically, I want to sort in the order " drop "," create "," insert "` ``.

In this case, since the elements of the set are limited, in SQL it is sufficient to sort by `` `case``` with the characteristic function. I want to do the same thing with java.

environment

java 1.8

code

Have a characteristic function in Map

It has a characteristic function equivalent in Map. key is an element of the set and value is an integer in the sort order.

Map<String, Integer> map = new HashMap<>();
map.put("drop", 1);
map.put("create", 2);
map.put("insert", 3);

List<String> list = Arrays.asList("insert", "create", "drop");
list.stream()
	.sorted((s1, s2) -> map.get(s1).compareTo(map.get(s2)))
	.forEach(System.out::println);

Output result.

drop
create
insert

Sort file names in any order

The situation where this was needed was that I wanted to sort the files in a particular order. For example, suppose you have a group of files like this.

0001_create.sql
0001_drop.sql
0001_insert.sql
0002_create.sql
0002_drop.sql
0002_insert.sql

I wanted to get the file list in the order of prefix + suffix in the above-mentioned [drop-> create-> insert].

So the source code.

Map<String, Integer> map = new HashMap<>();
map.put("drop.sql", 1);
map.put("create.sql", 2);
map.put("insert.sql", 3);

Files.walk(Paths.get("files"))
	.filter(Files::isRegularFile)
	.sorted((p1, p2) -> {
		String[] sp1 = p1.getFileName().toString().split("_");
		String[] sp2 = p2.getFileName().toString().split("_");

		String pp1 = sp1[0] + map.get(sp1[1]);
		String pp2 = sp2[0] + map.get(sp2[1]);
		return pp1.compareTo(pp2);})
	.forEach(System.out::println);

Output result.

files\0001_drop.sql
files\0001_create.sql
files\0001_insert.sql
files\0002_drop.sql
files\0002_create.sql
files\0002_insert.sql

That doesn't change what you do. Separate the file names with a separator and convert the suffix part to an integer in the sort order with a characteristic function map. If you attach them in the order of prefix, you will get the strings `" 00013 "," 00012 "," 00011 "```, so all you have to do is `compareTo```.

Sort strings functionally with java

environment

code

Have a characteristic function in Map

Sort file names in any order