How to extract numbers from a string

Question

String a = \"sin(23)+cos(4)+2!+3!+44!\";
a.replaceAll(\"\\D\"); //Not working it is only extracting Digits 

I want to extract the numbers which are wit

Answer 1

Use regular expression to find what you want:

String a = "sin(23)+cos(4)+2!+3!+44!";

Pattern pattern = Pattern.compile("\\d+!"); //import java.util.regex.Pattern
Matcher matcher = pattern.matcher(a);       //import java.util.regex.Matcher
while (matcher.find()) {
    System.out.print("Start index: " + matcher.start());
    System.out.print(" End index: " + matcher.end() + " -> ");
    System.out.println(matcher.group());
}

Output:

Start index: 15 End index: 17 -> 2!
Start index: 18 End index: 20 -> 3!
Start index: 21 End index: 24 -> 44!

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Further improvement:

With the following, you can cast the matcher.group(1) return value directly using Integer.parseInt():

Pattern pattern = Pattern.compile("(\\d+)!");
...
    System.out.println(matcher.group(1));

Output:

Start index: 15 End index: 17 -> 2
Start index: 18 End index: 20 -> 3
Start index: 21 End index: 24 -> 44

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Can you figure out the rest? You could use the index values to replace the matches in the original string, but be sure to start from the last one.