java, how to determine if a string contains a sub string in a particular order

Try this:

String regex = st2.chars()
                  .mapToObj(i -> String.valueOf((char) i))
                  .map(str -> ".*+?^${}()|[]\\".contains(str) ? "\\" + str : str)
                  .collect(Collectors.joining(".*", ".*", ".*"));

boolean contains = st1.matches(regex);

Here's a rundown:

• Get a regex string of the shorter string (st2 in our case - hardcoded - you can automate this of-course), adding .* in front and back, and between each character. (.* matches 0 or more of any character).

• String.chars() returns an IntStream, convert it to String with type cast

• As @Robert suggested, escape special characters with a backslash.

• Check of the longer string matches, which effectivelly means it contains all characters of the short string, and maybe more.

What you are looking for is a subsequence, not a substring.

Here's a working solution I found on geeksforgeeks:

// Recursive Java program to check if a string
// is subsequence of another string
import java.io.*;

class SubSequence
{
    // Returns true if str1[] is a subsequence of str2[]
    // m is length of str1 and n is length of str2
    static boolean isSubSequence(String str1, String str2, int m, int n)
    {
        // Base Cases
        if (m == 0) 
            return true;
        if (n == 0) 
            return false;

        // If last characters of two strings are matching
        if (str1.charAt(m-1) == str2.charAt(n-1))
            return isSubSequence(str1, str2, m-1, n-1);

        // If last characters are not matching
        return isSubSequence(str1, str2, m, n-1);
    }

    // Driver program
    public static void main (String[] args) 
    {
        String str1 = "database2.0version25";
        String str2 = "database2.0/version\"2-00\"";
        int m = str1.length();
        int n = str2.length();
        boolean res = isSubSequence(str1, str2, m, n);
        if(res)
            System.out.println("Yes");
        else
            System.out.println("No");
    }
}

// Contributed by Pramod Kumar

You can find the subsequence needle in the string haystack by looking for needle's characters in order, starting from an index searchFrom that you update as you find each successive character.

In the following code, note that haystack.indexOf(needleChar, searchFrom) returns the index of the first occurrence of needleChar starting from index searchFrom in haystack.

boolean contains(String haystack, String needle) {
    int searchFrom = 0;
    for (char needleChar : needle.toCharArray()) {
        searchFrom = haystack.indexOf(needleChar, searchFrom);
        if (searchFrom == -1) {
            return false;
        }
    }
    return true;
}