Commonly Used String Methods in Java

The String class in Java provides a variety of methods for manipulating strings. Here are some commonly used String methods:

1. Length of a String: length()
   Returns the length (number of characters) of a string.
   

   String str = "Hello, World!";
   int length = str.length(); // length will be 13

2. Accessing Characters: charAt(int index)
   Returns the character at the specified index.
   

   char firstChar = str.charAt(0); // firstChar will be 'H'

3. Substring: substring(int beginIndex) and substring(int beginIndex, int endIndex)
   - substring(int beginIndex): Returns a substring starting from the specified index.
   - substring(int beginIndex, int endIndex): Returns a substring from beginIndex (inclusive) to endIndex (exclusive).
   

   String substring1 = str.substring(7);       // substring1 will be "World!"
   String substring2 = str.substring(0, 5);    // substring2 will be "Hello"

4. Concatenation: concat(String str) or + operator
   - concat(String str): Concatenates the specified string to the end of the current string.
   - + operator: Concatenates two strings.
   

   String str1 = "Hello";
   String str2 = "World";
   String result = str1.concat(", " + str2); // result will be "Hello, World"

5. Comparison: equals(String anotherString) and equalsIgnoreCase(String anotherString)
   - equals(String anotherString): Compares the content of two strings for equality.
   - equalsIgnoreCase(String anotherString): Compares two strings, ignoring case.
   

   String s1 = "Hello";
   String s2 = new String("Hello");
   boolean isEqual = s1.equals(s2); // isEqual will be true

6. Search: indexOf(String str) and lastIndexOf(String str)
   - indexOf(String str): Returns the index within the string of the first occurrence of the specified substring.
   - lastIndexOf(String str): Returns the index within the string of the last occurrence of the specified substring.
   

   int index1 = str.indexOf("World");     // index1 will be 7
   int index2 = str.lastIndexOf("l");     // index2 will be 10

7. Changing Case: toUpperCase() and toLowerCase()
   Converts the entire string to uppercase or lowercase.
   

   String upperCaseStr = str.toUpperCase();     // upperCaseStr will be "HELLO, WORLD!"
   String lowerCaseStr = str.toLowerCase();     // lowerCaseStr will be "hello, world!"

8. Trimming: trim()
   Removes leading and trailing whitespaces from the string.
   

   String spacedStr = "    Hello, World!    ";
   String trimmedStr = spacedStr.trim(); // trimmedStr will be "Hello, World!"

9. Replacing Characters: replace(char oldChar, char newChar)
   Replaces all occurrences of a specified character with another character.
   

   String originalStr = "apple";
   String replacedStr = originalStr.replace('p', 'b'); // replacedStr will be "abble"

10. Splitting: split(String regex)
    Splits the string into an array of substrings based on a specified regular expression.
    

    String sentence = "The quick brown fox";
    String[] words = sentence.split(" "); // words will be {"The", "quick", "brown", "fox"}

These are just a few examples of the many methods available in the String class. Understanding and using these methods effectively can simplify string manipulation tasks in Java.