Extracting a pattern from a string in Java

Question

I have a String variable as follows in Java.

String s = "hello\nthis is java programme\n.class file will be generated after executing it\n";

Now I need to exctract the .class part from the above string variable. How to do that?

If you just need the `.class`, then just use `".class"`. I assume you wanted something else? Can you define it more precisely? Show what your output string should be? — RealSkeptic, Jan 16 '17 at 16:45
I'd suggest regex but I don't get your requirements. What would the `.class` part be? If it's just the literal then what do you mean by "extract"? — Thomas, Jan 16 '17 at 16:45
It is just a pattern I am trying to extract from the string. — Alla Sasikanth, Jan 16 '17 at 16:46
do you want everything up to the .class? after the .class? what? — RAZ_Muh_Taz, Jan 16 '17 at 16:47
Please provide more and better examples of that pattern. Would the string be something like `"yadda yadda ...\nWhatever.class file will be generated..."` and you want to extract `Whatever`? — Thomas, Jan 16 '17 at 16:48
Then you don't need the original string and you don't need to "extract" anything. If you want `.class`, use `System.out.println(".class")`. Otherwise, explain what you want in your output that has anything to do with your input. — RealSkeptic, Jan 16 '17 at 16:49
How about `String output = ".class";`? I know that sounds silly and is probably not what you are looking for _but we really don't know what it is that you want_. — Thomas, Jan 16 '17 at 16:49
If output should be `.class`, then write `String output = ".class";` and you're done. — Andreas, Jan 16 '17 at 16:50
@SasiKanth As you can see from previous comments, your description of what you want is extremely badly worded. Perhaps you should read: [How do I ask a good question?](http://stackoverflow.com/help/how-to-ask) — Andreas, Jan 16 '17 at 16:51

score 0 · Answer 1 · answered Jan 16 '17 at 17:12

I really only see one way for you to not simply just output ".class" which is to first see if the string contains ".class" before printing it. Here is a function to do so. Pass a string to look for and a string to search for it.

//Returns the string if found, else returns an empty string
public String FindString(String whatToFind, String whereToFind)
{
    return whereToFind.contains(whatToFind) ? whatToFind : "";
}

Output

String s = "hello\nthis is java programme\n.class file will be generated after executing it\n";
System.out.println(FindString(".class", s)); // prints .class

Poorya Hosseini · Answer 2 · 2017-01-23T12:58:24.850

if you just want to check if the string has ".class" pattern inside you can easily just check it like:

s.contains(".class");

Or if you want check that the pattern like .class inside your string that contains \n using regex:

Pattern p = Pattern.compile(".*\\.class.*", Pattern.DOTALL);
Matcher m = p.matcher(s);
boolean b = m.matches();

DOTALL enables \n also considered as a character.

s is the String you defined in your code.

score 0 · Answer 3 · edited May 23 '17 at 12:01

0

Use regular expressions, like in this answer

String s = "hello\nthis is java programme\n<some_class_name_here>.class file will be generated after executing it\n";
//the following pattern I think will find what you're looking for,
Pattern pattern = Pattern.compile("\n(.*\.class)");
Matcher matcher = pattern.matcher(s);
if (matcher.find())
{
    System.out.println(matcher.group(1));
}

edited May 23 '17 at 12:01

Community

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answered Jan 16 '17 at 18:29

DDoomUs

183
9

People really want to help you, but as the comments indicate, your question is not clear. I'll try to restate what I think you're asking: I have a `String` variable which has the following structure in Java. String s = "hello\nthis is java programme\n.class file will be generated after executing it\n"; Now I need to extract the `.class` part from the above string variable so that I have a variable with only the class and the .class portion of the string. How do I extract only the classname and .class bit of the String? – DDoomUs Jan 16 '17 at 18:31

Extracting a pattern from a string in Java

3 Answers3