regex - Find all occurrences of substring in string in Java -

i'm trying find occurrences of substring in string in java.

for example: searching "ababsdfasdfhelloasdf" "asdf" return [8,17] since there 2 "asdf"'s, 1 @ position 8 , 1 @ 17. searching "aaaaaa" "aa" return [0,1,2,3,4] because there "aa" @ positions 0,1,2,3, , 4.

i tried this:

public list<integer> findsubstrings(string inwords, string inword) {     string copyofwords = inwords;     list<integer> indicesofword = new arraylist<integer>();     int currentstartindex = niwords.indexof(inword);     int indexat = 0;     system.out.println(currentstartindex);     while (cthing1 > 0) {         indicesofword.add(currentstartindex+indexat);         system.out.println(currentstartindex);         system.out.println(indicesofword);         indexat += cthing1;         copyofwords = copyofwords.substring(cthing1);         system.out.println(copyofwords);         cthing1 = copyofwords.indexof(inword);     } 

this problem can solved in python follows:

indices = [m.start() m in re.finditer(word, a.lower())] 

where "word" word i'm looking , "a" string i'm searching through.

how can achieve in java?

you can use capturing inside positive look-ahead overlapping matches , use matcher#start indices of captured substrings.

as the regex, like

(?=(aa)) 

in java code:

string s = "aaaaaa"; matcher m = pattern.compile("(?=(aa))").matcher(s); list<integer> pos = new arraylist<integer>(); while (m.find()) {     pos.add(m.start()); } system.out.println(pos); 

result:

[0, 1, 2, 3, 4] 

see ideone demo