In Java, a string is an object that represents a sequence of characters. The java.lang.String class is used to create and manipulate strings in Java. Strings in Java are immutable, meaning that once a string object is created, its content cannot be changed. Any operation that appears to modify the content of a string actually creates a new string.

1. What is String in Java?
String is a class in Java that represents a sequence of characters. It
allows you to manipulate, query, and perform various operations on
textual data.

2. Creating and Initializing Strings
1 String Literal
Strings can be directly declared using double quotes, like "Hello, World!".
2 New Keyword
Strings can also be created using the new keyword and the String class
constructor.
3 String Concatenation
Combine strings using the concatenation operator (+) or the concat method.

3. Manipulating and Querying Strings
String Length
Use the length()
method to determine
the number of
characters in a string.
Substring
Extraction
Extract substrings
using substring()
to retrieve specific
portions of a string.
Replacing
Text
Replace occurrences
of a substring with
the replace()
method.
String
Splitting
Split a string into an
array of substrings
using split() based
on a specified
delimiter.

4. String Concatenation Methods
Method Description
concat(String str) Concatenates the specified string to the end of
the invoking string.
join(CharSequence delimiter,
CharSequence... elements)
Concatenates a sequence of elements with a
specified delimiter.
format(Locale l, String format, Object... args)
Returns a formatted string using the specified
format and arguments.

5. String Manipulation using Regular
Expressions
1 Pattern Matching
Find substrings that match a specific pattern using regular expressions.
2 Search and Replace
Perform global search and replace operations using regular expression patterns.
3 Validation and Formatting
Validate input or format strings using regular expressions for complex patterns.

6. String Comparison and Equality
Comparing Strings
Use the equals() method to compare the
content of two strings.
Case Insensitive Comparison
Perform case-insensitive string comparison
using equalsIgnoreCase().
Lexicographically Ordering
Compare strings based on their lexicographical
order using compareTo().
String Interning
Use intern() to store unique String objects in
the string pool for efficient memory usage.

7. Common Pitfalls and Best Practices
Null Checks
Always check for null values
before performing operations on
strings.
Immutable Nature
Remember that strings are
immutable, meaning they cannot
be changed once created.
String Constants
Prefer using constant strings
instead of hardcoding values for
better maintainability and
reusability.