Answer: String Handling Functions in Java

1. Introduction

In Java, a String is an object of the java.lang.String class that represents a sequence of characters.

• Immutability: Once created, a String object’s content cannot be modified. Any modification creates a new String object in memory (utilizing the String Constant Pool).
• For mutable strings, Java provides StringBuffer (thread-safe, synchronized) and StringBuilder (faster, non-synchronized).

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2. Core String Handling Methods

Method & Syntax	Description	Example
int length()	Returns the number of characters in the string.	"Hello".length() $\to$ 5
char charAt(int index)	Returns the character at the specified 0-based index.	"Java".charAt(1) $\to$ 'a'
String substring(int begin, int end)	Returns substring from begin (inclusive) to end (exclusive).	"Technology".substring(0, 4) $\to$ "Tech"
boolean equals(Object obj)	Compares character contents for exact equality (case-sensitive).	"Cat".equals("cat") $\to$ false
boolean equalsIgnoreCase(String s)	Compares strings ignoring uppercase/lowercase differences.	"Cat".equalsIgnoreCase("cat") $\to$ true
int compareTo(String s)	Compares strings lexicographically ($0$ if equal, negative if smaller, positive if greater).	"A".compareTo("B") $\to$ -1
String concat(String str)	Appends the specified string to the end.	"Web".concat("Tech") $\to$ "WebTech"
int indexOf(String str)	Returns index of first occurrence of the substring (or -1).	"banana".indexOf("na") $\to$ 2
int lastIndexOf(String str)	Returns index of last occurrence of the substring.	"banana".lastIndexOf("na") $\to$ 4
String toUpperCase()	Converts all characters to uppercase.	"java".toUpperCase() $\to$ "JAVA"
String toLowerCase()	Converts all characters to lowercase.	"HTML".toLowerCase() $\to$ "html"
String trim()	Eliminates leading and trailing whitespace.	" test ".trim() $\to$ "test"
String replace(char old, char new)	Replaces all occurrences of old with new.	"Java".replace('a', 'o') $\to$ "Jovo"
boolean contains(CharSequence s)	Checks if string contains the specified sequence.	"PYQDeck".contains("Deck") $\to$ true
boolean startsWith(String prefix)	Checks if string begins with specified prefix.	"http://".startsWith("http") $\to$ true
String[] split(String regex)	Splits the string into an array around matches of regex.	"a,b,c".split(",") $\to$ ["a", "b", "c"]
char[] toCharArray()	Converts string into a new character array.	"Hi".toCharArray() $\to$ ['H', 'i']

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3. Java Code Demonstration

public class StringHandlingDemo {
    public static void main(String[] args) {
        String s1 = " Bihar Engineering University ";
        
        System.out.println("Original String: '" + s1 + "'");
        System.out.println("Length: " + s1.length());
        System.out.println("Trimmed: '" + s1.trim() + "'");
        System.out.println("Uppercase: " + s1.toUpperCase());
        System.out.println("Character at index 7: " + s1.charAt(7));
        System.out.println("Substring (1-6): " + s1.substring(1, 6));
        System.out.println("Replaced: " + s1.replace("Bihar", "State"));
        System.out.println("Contains 'Engineering': " + s1.contains("Engineering"));

        // Splitting string
        String languages = "HTML,CSS,JavaScript,Java,PHP";
        String[] langArray = languages.split(",");
        System.out.println("
Split Elements:");
        for (String lang : langArray) {
            System.out.println(" - " + lang);
        }
    }
}

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4. String vs StringBuffer vs StringBuilder

Parameter	String	StringBuffer	StringBuilder
Storage	String Constant Pool / Heap	Heap	Heap
Mutability	Immutable	Mutable	Mutable
Thread Safety	Thread-safe (due to immutability)	Thread-safe (Synchronized)	Not Thread-safe
Performance	Slow on frequent concatenation	Medium	Fastest
Introduced	Java 1.0	Java 1.0	Java 1.5