Strings in Java

Strings in Java

Here’s a quick overview of some of the most important and commonly used String methods in Java (mostly written by ChatGpt 4-O)

1. length()

• Description: Returns the length of the string (number of characters).
• Usage:

  String str = "Hello";
  int len = str.length(); // 5
  

2. charAt(int index)

• Description: Returns the character at the specified index.
• Usage:

  char ch = str.charAt(0); // 'H'
  

3. substring(int beginIndex) and substring(int beginIndex, int endIndex)

• Description: Extracts a substring starting from beginIndex (inclusive) and optionally up to endIndex (exclusive).
• Usage:

  String sub = str.substring(1); // "ello"
  String sub2 = str.substring(0, 2); // "He"
  

4. indexOf(String str) and indexOf(char ch)

• Description: Returns the index of the first occurrence of the specified character or substring. Returns -1 if not found.
• Usage:

  int index = str.indexOf('e'); // 1
  int index2 = str.indexOf("lo"); // 3
  

5. lastIndexOf(String str) and lastIndexOf(char ch)

• Description: Returns the index of the last occurrence of the specified character or substring.
• Usage:

  int lastIndex = str.lastIndexOf('l'); // 3
  

6. equals(Object obj) and equalsIgnoreCase(String anotherString)

• Description: Compares two strings for equality. equalsIgnoreCase() ignores case.
• Usage:

  boolean isEqual = str.equals("Hello"); // true
  boolean isEqualIgnoreCase = str.equalsIgnoreCase("hello"); // true
  

7. compareTo(String anotherString) and compareToIgnoreCase(String anotherString)

• Description: Compares two strings lexicographically. Returns a negative, zero, or positive integer depending on whether the string is less than, equal to, or greater than the compared string.
• Usage:

  int result = str.compareTo("Hello"); // 0 (equal)
  int resultIgnoreCase = str.compareToIgnoreCase("hello"); // 0 (equal ignoring case)
  

8. contains(CharSequence s)

• Description: Returns true if the string contains the specified sequence of characters.
• Usage:

  boolean containsSub = str.contains("ell"); // true
  

9. toUpperCase() and toLowerCase()

• Description: Converts all characters in the string to uppercase or lowercase.
• Usage:

  String upper = str.toUpperCase(); // "HELLO"
  String lower = str.toLowerCase(); // "hello"
  

10. trim()

• Description: Removes leading and trailing whitespace from the string.
• Usage:

  String trimmed = "  Hello  ".trim(); // "Hello"
  

11. replace(char oldChar, char newChar) and replaceAll(String regex, String replacement)

• Description: Replaces all occurrences of a specified character or substring. replaceAll() allows regex replacement. (A regex is a regular expression. Feel free to read about them if you’re interested! The regex ‘\d’ matches any digit. The extra ‘')
• Usage:

  String replaced = str.replace('l', 'x'); // "Hexxo"
  String replacedAll = "foo123bar".replaceAll("\\d", ""); // "foobar" (removes digits)
  

12. split(String regex)

• Description: Splits the string into an array based on a regular expression delimiter.
• Usage:

  String[] parts = "apple,orange,banana".split(","); // ["apple", "orange", "banana"]
  

13. join(CharSequence delimiter, CharSequence... elements)

• Description: Joins multiple strings with the specified delimiter.
• Usage:

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

14. startsWith(String prefix) and endsWith(String suffix)

• Description: Checks if the string starts or ends with the specified prefix or suffix.
• Usage:

  boolean starts = str.startsWith("He"); // true
  boolean ends = str.endsWith("lo"); // true
  

15. isEmpty() and isBlank()

• Description: isEmpty() returns true if the string’s length is 0. isBlank() returns true if the string is empty or contains only whitespace.
• Usage:

  boolean empty = "".isEmpty(); // true
  boolean blank = "   ".isBlank(); // true
  

16. valueOf()

• Description: Converts various data types (int, float, boolean, etc.) to a string.
• Usage:

  String numStr = String.valueOf(123); // "123"
  

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