does text contains substring

Question

How to check if some String contains a specific String like "ABC72961". So we search for String which starts with "ABC" following by 5 digits. I've implemented a algorithm but I want it with "matches" or somehow else and then check the speed of these two solutions.

Answer 1

You may want to use regex for this

^ABC[0-9]{5}$

• ^ : Beginning of the string
• ABC : Matches ABC literally (case-sensitive)
• [0-9]{5} : Matches 5x numbers from 0 to 9
• $ : End of the string

And use String#matches to test it

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Regex101

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Example

String regex = "^ABC[0-9]{5}$";
String one = "ABC72961";
String two = "ABC2345";
String three = "AB12345";
String four = "ABABABAB";

System.out.println(one.matches(regex));      // true
System.out.println(two.matches(regex));      // false
System.out.println(three.matches(regex));    // false
System.out.println(four.matches(regex));     // false

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EDIT

Seeing your comment, you want it to work for String one = "textABC72961text" also. For that to be possible, you should just erase ^ and $ that limit the String.

.*ABC[0-9]{5}.*

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EDIT 2

Here is if you want to extract it

if (s.matches(".*ABC[0-9]{5}.*")) {
    Matcher m = Pattern.compile("ABC[0-9]{5}").matcher(s);
    m.find();
    result = m.group();
}

Answer 2

You can use the String indexOf command like this:

int result = someString.indexOf("ABC72961")

result will be -1 if there are no matches.

If there is a match, the result will be the index where the match starts.

Answer 3

str.contains("ABC72961");

Returns true if str contains the string. False if not.

Answer 4

I think what you want to use is java.util.regex.Pattern.

Pattern p = Pattern.compile("ABC(\d*)"); 
Matcher m = p.matcher("ABC72961"); 
boolean b = m.matches();

or if it shall be exactly 5 digits after "ABC", you can use the regex ABC(\d{5})

https://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html#compile(java.lang.String)

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Another solution would be:

String stringToTest = "ABC72961"
boolean b = stringToTest.contains("ABC");

http://www.tutorialspoint.com/java/lang/string_contains.htm

Answer 5

public String getString() {
        String str = extractString();
        return str;
    }

    public boolean exists() {
        return !getString().trim().equals("") ? false : true;
    }

    private List<Integer> getPositionsOfABC() {
        List<Integer> positions = new ArrayList<>();
        int index = text.indexOf("ABC");
        while (index > 0) {
            positions.add(index);
            index = text.indexOf("ABC", index + 1);
        }
        return positions;
    }

    private static boolean isInteger(String str) {
        boolean isValidInteger = false;
        try {
            Integer.parseInteger(str);
            isValidInteger = true;
        } catch (NumberFormatException ex) {
            return isValidInteger;
        }
        return isValidInteger;
    }

    private String extractString() {
        List<Integer> positions = getPositionsOfABC();
        for (Integer position : positions) {
            int index = position.intValue();
            String substring = text.substring(index, index + LENGTH_OF_DIGITS);
            String lastDigits = substring.substring(3, substring.length());
            if (isInteger(lastDigits)) {
                return substring;
            }
        }
        return "";
    }

Answer 6

Here's a simple code that checks whether a substring exists in a string without using library functions, regex or other complex data structures.

class SSC {
public static void main(String[] args) {
    String main_str <-- MAIN STRING
    String sub_str <-- SUBSTRING
    String w; int flag=0;
    for(int i=0;i<=main_str.length()-sub_str.length();i++){
        w="";
        for(int j=0;j<sub_str.length();j++){
            w+=main_str.charAt(i+j);
        }
        if(w.equals(sub_str))
        flag++;
    }
    if(flag>0)
    System.out.print("exists "+flag+" times");
    else
    System.out.print("doesn't exist");  
  }
}

Hope this helps.