Java - second last occurrence of char in string

It seems like every single answer is assuming that you already know the input string and the exact position of the last occurrence of "/" in it, when that is usually not the case...
Here's a more general method to obtain the nth-last (second-last, third-last, etc.) occurrence of a character inside a string:

static int nthLastIndexOf(int nth, String ch, String string) {
    if (nth <= 0) return string.length();
    return nthLastIndexOf(--nth, ch, string.substring(0, string.lastIndexOf(ch)));
}

Usage:

    String s = "the/quick/brown/fox/jumped/over/the/lazy/dog/";
    System.out.println(s.substring(0, nthLastIndexOf(2, "/", s)+1)); // substring up to 2nd last included
    System.out.println(s.substring(0, nthLastIndexOf(3, "/", s)+1)); // up to 3rd last inc.
    System.out.println(s.substring(0, nthLastIndexOf(7, "/", s)+1)); // 7th last inc.
    System.out.println(s.substring(0, nthLastIndexOf(2, "/", s))); // 2nd last, char itself excluded

Output:

the/quick/brown/fox/jumped/over/the/lazy/
the/quick/brown/fox/jumped/over/the/
the/quick/brown/
the/quick/brown/fox/jumped/over/the/lazy

This works, given path length >2

final String path = "the/quick/brown/fox/jumped/over/the/lazy/dog/";
final int secondLast = path.length()-2;
final String output = path.substring(0, path.lastIndexOf("/",secondLast)+1);
System.out.println(output);

The lastIndexOf method's second parameter specifies the maximum index upto where the method should search the string. This means, that in your case

path.lastIndexOf("/", 1)

returns the first index of "/" whose index is smaller than 1.

First of all, lastIndexOf will return an index, not a string. It also searches backwards from the specified index 1, so it will only look at everything before and including the character at index 1. This means that it only checks t and h. Expectedly, it finds nothing and returns -1.

You should just omit the second argument if you want to search the whole string.

In addition, to achieve your desired output string (I assume you want the last path component removed?), you can use replaceAll with a regex:

String output = path.replaceAll("[^/]+/$", "");

Using Apache Commons IO

String output = org.apache.commons.io.FilenameUtils.getPath(path);

Not using Apache

public static String removeLastPart(String str) {
    int pos = str.length() - 1;

    while (str.charAt(pos) != '/' || pos + 1 == str.length()) {
        pos--;
    }

    return str.substring(0, pos + 1);
}

If you are dealing with paths and files why not use the built in classes? Something like below seems to me easier than string manipulation:

Path path = Paths.get("the/quick/brown/fox/jumped/over/the/lazy/dog/");
System.out.println(path.getParent());
// prints: the\quick\brown\fox\jumped\over\the\lazy
System.out.println(path.getParent().getParent());
// prints: the\quick\brown\fox\jumped\over\the

For example, String key = "aaa/bbb/ccc/ddd" ;

and i need my result string as "ccc/ddd". which is, sub-string of second last index of "/", The following code helps ::

    String key="aaa/bbb/ccc/ddd";
    key=key.substring(key.substring(0, key.lastIndexOf("/")).lastIndexOf("/")+1);

The final value of key will be "ccc/ddd".

Try - 1 approach:

int j = path.lastIndexOf("/");
int i = path.lastIndexOf("/", j - 1);      // the 2nd last index from the last index

String output = path.substring(0, i + 1);  // inclusive

Here's an use case:

        String url = "http://localhost:4000/app/getPTVars";
        int secondLastIndexOf = url.substring(0, url.lastIndexOf('/')).lastIndexOf('/');
        System.out.println(secondLastIndexOf);
        System.out.println(url.substring(secondLastIndexOf, url.length()));

and the output:

21
/app/getPTVars

String path = "the/quick/brown/fox/jumped/over/the/lazy/dog/";

String output = path.substring(0, path.lastIndexOf("/",path.lastIndexOf("/")-1)+1);