Java: method to get position of a match in a String?

Solution 1:

The family of methods that does this are:

int indexOf(String str)
- indexOf(String str, int fromIndex)
int lastIndexOf(String str)
- lastIndexOf(String str, int fromIndex)

Returns the index within this string of the first (or last) occurrence of the specified substring [searching forward (or backward) starting at the specified index].

String text = "0123hello9012hello8901hello7890";
String word = "hello";

System.out.println(text.indexOf(word)); // prints "4"
System.out.println(text.lastIndexOf(word)); // prints "22"

// find all occurrences forward
for (int i = -1; (i = text.indexOf(word, i + 1)) != -1; i++) {
    System.out.println(i);
} // prints "4", "13", "22"

// find all occurrences backward
for (int i = text.length(); (i = text.lastIndexOf(word, i - 1)) != -1; i++) {
    System.out.println(i);
} // prints "22", "13", "4"

Solution 2:

This works using regex.

String text = "I love you so much";
String wordToFind = "love";
Pattern word = Pattern.compile(wordToFind);
Matcher match = word.matcher(text);

while (match.find()) {
     System.out.println("Found love at index "+ match.start() +" - "+ (match.end()-1));
}

Output :

Found 'love' at index 2 - 5

General Rule :

Regex search left to right, and once the match characters has been used, it cannot be reused.

Solution 3:

text.indexOf(match);

See the String javadoc

Solution 4:

Finding a single index

As others have said, use text.indexOf(match) to find a single match.

String text = "0123456789hello0123456789";
String match = "hello";
int position = text.indexOf(match); // position = 10

Finding multiple indexes

Because of @StephenC's comment about code maintainability and my own difficulty in understanding @polygenelubricants' answer, I wanted to find another way to get all the indexes of a match in a text string. The following code (which is modified from this answer) does so:

String text = "0123hello9012hello8901hello7890";
String match = "hello";

int index = text.indexOf(match);
int matchLength = match.length();
while (index >= 0) {  // indexOf returns -1 if no match found
    System.out.println(index);
    index = text.indexOf(match, index + matchLength);
}

Solution 5:

You can get all matches in a file simply by assigning inside while-loop, cool:

$ javac MatchTest.java 
$ java MatchTest 
1
16
31
46
$ cat MatchTest.java 
import java.util.*;
import java.io.*;

public class MatchTest {
    public static void main(String[] args){
        String match = "hello";
        String text = "hello0123456789hello0123456789hello1234567890hello3423243423232";
        int i =0;
        while((i=(text.indexOf(match,i)+1))>0)
            System.out.println(i);
    }
}