How to know if a given string is substring from another string in Java

How to know if a given string is substring from another string in Java

In Java, you can check if a given string is a substring of another string using the contains method from the String class. Here is a straightforward example of how to achieve this:

Example

public class SubstringCheck { public static void main(String[] args) { String mainString = "Hello, welcome to the world of Java!"; String subString = "welcome"; if (mainString.contains(subString)) { System.out.println("\"" + subString + "\" is a substring of \"" + mainString + "\""); } else { System.out.println("\"" + subString + "\" is NOT a substring of \"" + mainString + "\""); } } }

Explanation

  • contains Method: The contains method is a built-in method in the String class that returns true if and only if the string contains the specified sequence of characters.
  • Case Sensitivity: The contains method is case-sensitive. If you need a case-insensitive check, you can convert both strings to the same case (e.g., using toLowerCase() or toUpperCase()) before performing the check.

Case-Insensitive Example

If you need the check to be case-insensitive:

public class SubstringCheck { public static void main(String[] args) { String mainString = "Hello, welcome to the world of Java!"; String subString = "WELCOME"; if (mainString.toLowerCase().contains(subString.toLowerCase())) { System.out.println("\"" + subString + "\" is a substring of \"" + mainString + "\" (case-insensitive)"); } else { System.out.println("\"" + subString + "\" is NOT a substring of \"" + mainString + "\" (case-insensitive)"); } } }

Alternative Methods

  1. Using indexOf:

    The indexOf method returns the index within the string of the first occurrence of the specified substring. If the substring is not found, it returns -1.

    if (mainString.indexOf(subString) != -1) { System.out.println("\"" + subString + "\" is a substring of \"" + mainString + "\""); } else { System.out.println("\"" + subString + "\" is NOT a substring of \"" + mainString + "\""); }

  2. Using Regular Expressions:

    You can use the Pattern and Matcher classes for more complex substring checks, including case-insensitive checks.

    import java.util.regex.Pattern; import java.util.regex.Matcher; public class SubstringCheck { public static void main(String[] args) { String mainString = "Hello, welcome to the world of Java!"; String subString = "WELCOME"; Pattern pattern = Pattern.compile(Pattern.quote(subString), Pattern.CASE_INSENSITIVE); Matcher matcher = pattern.matcher(mainString); if (matcher.find()) { System.out.println("\"" + subString + "\" is a substring of \"" + mainString + "\" (using regex)"); } else { System.out.println("\"" + subString + "\" is NOT a substring of \"" + mainString + "\" (using regex)"); } } }

Summary

  • contains Method: Simple and straightforward for case-sensitive checks.
  • Case-Insensitive Check: Convert both strings to the same case.
  • indexOf Method: Another simple method to find the position of a substring.
  • Regular Expressions: Useful for complex and case-insensitive substring searches.

Choose the method that best fits your needs based on the complexity and case sensitivity of your substring search.

Examples

  1. Java check if string contains substring

    • Description: Users want to check if a string contains another substring in Java and perform an action based on the result.
    • Code:
      String mainString = "This is the main string"; String subString = "main"; boolean containsSubstring = mainString.contains(subString); if (containsSubstring) { System.out.println("Substring found!"); } else { System.out.println("Substring not found."); }
    • This code uses the contains() method of the String class to check if mainString contains subString.

  2. Java substring check case insensitive

    • Description: Users search for how to perform a case-insensitive check to determine if one string is a substring of another in Java.
    • Code:
      String mainString = "This is the Main String"; String subString = "main"; boolean containsSubstring = mainString.toLowerCase().contains(subString.toLowerCase()); if (containsSubstring) { System.out.println("Substring found!"); } else { System.out.println("Substring not found."); }
    • Convert both mainString and subString to lowercase using toLowerCase() before applying the contains() method for case-insensitive comparison.

  3. Java substring search index

    • Description: This query focuses on finding the starting index of a substring within another string in Java.
    • Code:
      String mainString = "Hello world, welcome to Java"; String subString = "world"; int index = mainString.indexOf(subString); if (index != -1) { System.out.println("Substring found at index: " + index); } else { System.out.println("Substring not found."); }
    • The indexOf() method returns the starting index of subString within mainString. If subString is not found, it returns -1.

  4. Java substring contains method

    • Description: Users want to use the contains() method effectively to check substring presence in another string in Java.
    • Code:
      String mainString = "Java programming"; String subString = "gram"; boolean containsSubstring = mainString.contains(subString); if (containsSubstring) { System.out.println("Substring found!"); } else { System.out.println("Substring not found."); }
    • Demonstrates using the contains() method directly to check if mainString contains subString.

  5. Java substring match

    • Description: This query seeks to match a substring exactly within another string in Java.
    • Code:
      String mainString = "The quick brown fox jumps over the lazy dog"; String subString = "quick brown"; boolean isSubstringMatch = mainString.matches(".*" + subString + ".*"); if (isSubstringMatch) { System.out.println("Exact substring match found!"); } else { System.out.println("Exact substring match not found."); }
    • Uses regular expressions (matches()) to check if subString exists exactly within mainString.

  6. Java substring contains ignore case

    • Description: Users are interested in performing a case-insensitive check to see if a string contains another string in Java.
    • Code:
      String mainString = "Java Programming Language"; String subString = "programming"; boolean containsSubstring = mainString.toLowerCase().contains(subString.toLowerCase()); if (containsSubstring) { System.out.println("Substring found!"); } else { System.out.println("Substring not found."); }
    • Converts both mainString and subString to lowercase using toLowerCase() to perform a case-insensitive contains() check.

  7. Java substring exists

    • Description: This query focuses on determining if a substring exists within another string without explicitly finding its index.
    • Code:
      String mainString = "Java is awesome"; String subString = "is"; boolean substringExists = mainString.contains(subString); if (substringExists) { System.out.println("Substring exists in the main string."); } else { System.out.println("Substring does not exist in the main string."); }
    • Uses contains() to check if mainString contains subString and prints the result accordingly.

  8. Java substring match case sensitive

    • Description: Users want to verify if a substring matches exactly within another string in Java in a case-sensitive manner.
    • Code:
      String mainString = "Hello world"; String subString = "hello"; boolean isSubstringMatch = mainString.contains(subString); if (isSubstringMatch) { System.out.println("Substring matches exactly (case sensitive)."); } else { System.out.println("Substring does not match exactly (case sensitive)."); }
    • Uses contains() to check if mainString contains subString exactly as specified.

  9. Java substring check performance

    • Description: This query focuses on the performance implications of checking for a substring within a string in Java.
    • Code:
      String mainString = "This is a long string with some content"; String subString = "content"; boolean containsSubstring = mainString.contains(subString); if (containsSubstring) { System.out.println("Substring found!"); } else { System.out.println("Substring not found."); }
    • Demonstrates the straightforward use of contains() for substring checks without addressing performance optimizations explicitly.

  10. Java substring contains method performance

    • Description: Users are interested in understanding the performance characteristics of the contains() method when used for substring checks in Java.
    • Code:
      String mainString = "A large string to test substring performance"; String subString = "substring"; boolean containsSubstring = mainString.contains(subString); if (containsSubstring) { System.out.println("Substring found!"); } else { System.out.println("Substring not found."); }
    • Provides a basic example of using contains() for substring checks without delving into detailed performance analysis.

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