Java.lang.String class in Java | Set 2

The String class in Java provides a rich set of methods for performing string manipulation, comparison, searching, formatting, and Unicode handling. Since strings are immutable, these methods return new values without modifying the original string object.

• The String class belongs to the java.lang package.
• Supports Unicode character processing.
• Provides methods for searching and comparing strings.

String Class Methods

1. codePointAt(int index): It returns the Unicode code point of the character at the specified index.

Syntax:

int codePointAt(int index)

Example:

int cp = "Java".codePointAt(1);
System.out.println(cp);

2. codePointBefore(int index): Returns the Unicode code point of the character before the specified index.

Syntax:

int codePointBefore(int index)

Example:

int cp = "Java".codePointBefore(2);
System.out.println(cp);

3. codePointCount(int beginIndex, int endIndex): Returns the number of Unicode code points in the specified range.

Syntax:

int codePointCount(int beginIndex, int endIndex)

Example:

int count = "Hello".codePointCount(0, 5);
System.out.println(count);

4.subSequence(int beginIndex, int endIndex): Returns a CharSequence that is a subsequence of the string.

Syntax:

CharSequence subSequence(int beginIndex, int endIndex)

Example:

CharSequence cs = "Programming".subSequence(0, 7);
System.out.println(cs);

5. contains(CharSequence s): Checks if the string contains the specified sequence.

Syntax:

boolean contains(CharSequence s)

Example:

boolean result = "Java Programming".contains("Program");
System.out.println(result);

6. contentEquals(CharSequence s): Checks if the given CharSequence exactly matches the string.

Syntax:

boolean contentEquals(CharSequence s)

Example:

boolean result =
"Java".contentEquals(new StringBuilder("Java"));
System.out.println(result);

7. endsWith(String suffix): Returns true if the string ends with the specified suffix.

Syntax:

boolean endsWith(String suffix)

Example:

boolean result = "file.txt".endsWith(".txt");
System.out.println(result);

8. startsWith(String prefix): Returns true if the string starts with the specified prefix.

Syntax:

boolean startsWith(String prefix)

Example:

boolean result = "https://example.com".startsWith("https");
System.out.println(result);

9. getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin): Copies characters from a string into a destination character array.

Syntax:

void getChars(int srcBegin,
int srcEnd,
char[] dst,
int dstBegin)

Example:

char[] arr = new char[4];
"Java".getChars(0, 4, arr, 0);
System.out.println(arr);

10. toCharArray(): Converts the entire string into a new character array.

Syntax:

char[] toCharArray()

Example:

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

Note: Use getChars() when copying partial content into an existing array.

11. hashCode(): Returns the hash code for the string using the formula:

Syntax:

int hashCode()

Example:

int hash = "Java".hashCode();
System.out.println(hash);

12. intern(): Returns the canonical representation of the string from the String pool.

Syntax:

String intern()

Example:

String s1 = new String("Java").intern();

13. isEmpty(): Returns true if the string length is 0.

Syntax:

boolean isEmpty()

Example:

boolean result = "".isEmpty();
System.out.println(result);

14. format(String format, Object... args): Returns a formatted string using format specifiers.

Syntax:

static String format(String format, Object... args)

Example:

String s = String.format("Age: %d", 25);
System.out.println(s);

15. matches(String regex): Checks if the string matches the given regular expression.

Syntax:

boolean matches(String regex)

Example:

boolean valid = "abc123".matches("[a-z]+\\d+");
System.out.println(valid);

16. regionMatches(...): Compares a region of one string with a region of another string.

Syntax:

boolean regionMatches(int toffset,
String other,
int ooffset,
int len)

Example:

boolean result = "HelloWorld".regionMatches( 5, "World", 0, 5);
System.out.println(result);

17. split(String regex): Splits the string using a regular expression.

Syntax:

String[] split(String regex)

Example:

String[] parts = "A,B,C".split(",");

18. join(CharSequence delimiter, CharSequence... elements): Joins elements using the specified delimiter.

Syntax:

static String join(CharSequence delimiter, CharSequence... elements)

Example:

String s =String.join("-", "2025", "04", "30");
System.out.println(s);

19. replaceAll(String regex, String replacement): Replaces all occurrences matching the regex.

Syntax:

String replaceAll(String regex, String replacement)

Example:

String s ="a1b2".replaceAll("\\d", "");
System.out.println(s);

20. replaceFirst(String regex, String replacement): Replaces only the first matching occurrence.

Syntax:

String replaceFirst(String regex, String replacement)

Example:

String s = "a1b2".replaceFirst("\\d", "");
System.out.println(s);

Advantages of String Class Methods

• Efficient Text Processing: Provides built-in methods for searching, comparing, and manipulating strings.
• Unicode Support: Methods like codePointAt() and codePointCount() help work with Unicode characters accurately.
• Easy String Validation: Methods such as contains(), startsWith(), endsWith(), and matches() simplify data validation.
• Powerful Pattern Matching: Regular expression support through matches(), split(), replaceAll(), and replaceFirst().
• Simplified String Comparison: Methods like contentEquals() and regionMatches() enable flexible string comparisons.