2.7 String Methods

Frequently Asked Questions (FAQs) About String Methods

1. What are string methods in programming?

   String methods are built-in functions in programming languages that operate on strings to perform specific tasks like modifying, searching, or analyzing string data. Examples include substring(), length(), and toUpperCase().

2. How do you find the length of a string?

   Use the length() method:

   String text = "hello";
   int len = text.length();

3. What is the purpose of the charAt() method?

   The charAt() method retrieves a character at a specific index in a string.

   String text = "hello";
   char c = text.charAt(1); // 'e'

4. How do you check if a string is empty?

   Use the isEmpty() method:

   String text = "";
   boolean result = text.isEmpty(); // true

5. What is the difference between equals() and equalsIgnoreCase()?

   • equals(): Checks for exact case-sensitive equality.

   • equalsIgnoreCase(): Checks equality ignoring case differences.

6. How do you concatenate strings?

   Use the concat() method or the + operator:

   String text = "Hello".concat(" World");

7. What does the substring() method do?

   The substring() method extracts a part of a string:

   String text = "hello";
   String sub = text.substring(1, 4); // "ell"

8. How do you replace characters in a string?

   Use the replace() method:

   String text = "hello";
   String replaced = text.replace('l', 'p'); // "heppo"

9. What is the toUpperCase() method?

   Converts all characters in a string to uppercase:

   String text = "hello";
   String upper = text.toUpperCase(); // "HELLO"

10. What is the toLowerCase() method?

    Converts all characters in a string to lowercase:

    String text = "HELLO";
    String lower = text.toLowerCase(); // "hello"

11. How do you split a string?

    Use the split() method to divide a string into substrings based on a delimiter:

    String text = "apple,banana,grape";
    String[] fruits = text.split(",");

12. What does the trim() method do?

    Removes leading and trailing whitespace from a string:

    String text = " hello ";
    String trimmed = text.trim(); // "hello"

13. How do you check if a string starts with a specific prefix?

    Use the startsWith() method:

    String text = "hello";
    boolean result = text.startsWith("he"); // true

14. How do you check if a string ends with a specific suffix?

    Use the endsWith() method:

    String text = "hello";
    boolean result = text.endsWith("lo"); // true

15. What is the contains() method?

    Checks if a string contains a specific sequence:

    String text = "hello";
    boolean result = text.contains("ell"); // true

16. How do you find the index of a character or substring?

    Use the indexOf() method:

    String text = "hello";
    int index = text.indexOf('e'); // 1

17. What is the lastIndexOf() method?

    Finds the last occurrence of a character or substring:

    String text = "hello hello";
    int index = text.lastIndexOf("hello"); // 6

18. How do you check if two strings are equal?

    Use the equals() method:

    String text1 = "hello";
    String text2 = "hello";
    boolean result = text1.equals(text2); // true

19. Can you reverse a string using a method?

    Java doesn’t have a built-in reverse() method for strings, but you can use StringBuilder:

    String text = "hello";
    String reversed = new StringBuilder(text).reverse().toString();

20. What is the valueOf() method?

    Converts data types into strings:

    int num = 123;
    String text = String.valueOf(num); // "123"

21. What does the matches() method do?

    Checks if a string matches a regular expression:

    String text = "hello123";
    boolean result = text.matches(".*\d+"); // true

22. How do you join multiple strings?

    Use String.join():

    String joined = String.join(", ", "apple", "banana", "grape");

23. What is the format() method?

    Formats strings using placeholders:

    String result = String.format("%s is %d years old", "John", 25);

24. How do you check if a string is blank?

    Use the isBlank() method (Java 11+):

    String text = "  ";
    boolean result = text.isBlank(); // true

25. What is the difference between isEmpty() and isBlank()?

    • isEmpty(): Checks if the string is empty (length = 0).

    • isBlank(): Checks if the string contains only whitespace or is empty.

26. How do you convert a string to a character array?

    Use toCharArray():

    char[] chars = "hello".toCharArray();

27. What does the intern() method do?

    Ensures a string is stored in the string pool:

    String text = new String("hello").intern();

28. How do you repeat a string multiple times?

    Use the repeat() method (Java 11+):

    String text = "hello".repeat(3); // "hellohellohello"

29. What is the strip() method?

    Removes leading and trailing whitespace, including Unicode spaces (Java 11+):

    String text = " hello ";
    String stripped = text.strip(); // "hello"

30. What is the difference between trim() and strip()?

    • trim(): Removes ASCII spaces only.

    • strip(): Removes all types of whitespace, including Unicode.

31. How do you replace all occurrences of a substring?

    Use replaceAll():

    String text = "hello world";
    String result = text.replaceAll("o", "0"); // "hell0 w0rld"

32. What is the replaceFirst() method?

    Replaces the first occurrence of a substring:

    String text = "hello hello";
    String result = text.replaceFirst("hello", "hi"); // "hi hello"

33. How do you convert a string to an integer?

    Use Integer.parseInt():

    int num = Integer.parseInt("123");

34. What does the compareTo() method do?

    Compares two strings lexicographically:

    String a = "apple";
    String b = "banana";
    int result = a.compareTo(b); // Negative value

35. What is compareToIgnoreCase()?

    Compares strings lexicographically, ignoring case differences.

36. How do you convert a string to a double?

    Use Double.parseDouble():

    double num = Double.parseDouble("123.45");

37. What is the regionMatches() method?

    Compares specific regions of two strings:

    String text1 = "hello";
    String text2 = "yellow";
    boolean result = text1.regionMatches(1, text2, 1, 3); // true

38. How do you convert a string to a boolean?

    Use Boolean.parseBoolean():

    boolean flag = Boolean.parseBoolean("true");

39. How do you find if a string matches a prefix using an offset?

    Use startsWith() with an offset:

    String text = "hello world";
    boolean result = text.startsWith("world", 6); // true

40. What is the subSequence() method?

    Extracts a subsequence of characters:

    CharSequence seq = "hello".subSequence(1, 4); // "ell"

41. How do you sort a list of strings?

    Use Collections.sort():

    Collections.sort(stringList);

42. Can you use strings in switch cases?

    Yes, Java 7+ allows strings in switch cases.

43. What is the join() method?

    Concatenates multiple strings with a delimiter:

    String result = String.join(", ", "apple", "banana");

44. How do you convert a string to a long?

    Use Long.parseLong():

    long num = Long.parseLong("123456789");

45. How do you convert a string to a float?

    Use Float.parseFloat():

    float num = Float.parseFloat("123.45");

46. What is string interning?

    String interning ensures that identical strings share the same memory location to save space.

47. How do you escape special characters in a string?

    Use escape sequences like \n for newlines or \t for tabs.

48. What is the codePointAt() method?

    Returns the Unicode code point at a specific index:

    int codePoint = "hello".codePointAt(1); // 101

49. What is the compare() method?

    Compares two strings using a comparator.

50. How do you use String.format() for localization?

    Combine String.format() with Locale:

    String result = String.format(Locale.FRANCE, "%.2f", 1234.56);