All About String In Java

String in Java is immutable and stored in memory pool. Learn about StringBuffer, StringBuilder, and string manipulation techniques in Java.

In Java, String represents a sequence of characters. It is an immutable object, meaning once it is created, its value cannot be modified. If a string is updated, a new String object is created with the same reference. This behavior makes string manipulation in Java memory-efficient and secure.

Let’s start with a basic example:
String str = “India”;
System.out.println(str); // Output: India
String ctr = new String(“India”);
String ptr = “India”;
String ktr = str;
str = str + “n”; // Now str points to a new object
System.out.println(str); // Output: Indian
How many objects and references?
Number of references: 4 (str, ctr, ptr, ktr)

Number of objects: 3

Ways to Create a String
By string literal:

String str = “India”;
By using new keyword:

String ptr = new String(“India”);
Java String Pool
The Java String Pool is a memory area inside the heap where string literals are stored. It helps in memory optimization by avoiding the creation of duplicate strings.

Common Java String Methods
Java provides many built-in string methods in Java that help in manipulating and analyzing string data. These are part of the java.lang.String class.

String str = “Welcome to Cyberinfomines.com”;
System.out.println(str);
Frequently Used Java String Functions:

length() — Returns the length of the string.

int size = str.length();
System.out.println(“Length: “ + size); // 29
charAt(int index) — Returns character at specific index.

substring(int beginIndex) — Extracts substring from beginIndex.

substring(int begin, int end) — Extracts substring from begin to end-1.

indexOf(String s) — Returns first index of given substring.

contains(CharSequence s) — Checks if the string contains a specific sequence.

toUpperCase(), toLowerCase() — Converts string to upper/lowercase.

trim() — Removes leading/trailing whitespace.

split(String regex) — Splits string into array using regex.

concat(String str) — Appends given string.

equals(), equalsIgnoreCase() — Compares strings.

compareTo(), compareToIgnoreCase() — Lexicographic comparison.

hashCode() — Returns hash code.

isEmpty() — Checks if string length is 0.

lastIndexOf() — Finds last index of a character or substring.

valueOf() — Converts different types (boolean, char, int, etc.) to string.

These java string methods are widely used in interview questions and real-world development scenarios.

Use Case: Short Name Generation
public class StringBasic {
public static String getShortName(String firstName, String lastName, String surName) {
String shortName = firstName.toUpperCase().charAt(0) + “.” +
lastName.toUpperCase().charAt(0) + “.” +
surName.toUpperCase().charAt(0) + surName.toLowerCase().substring(1);
return shortName;
}
public static void main(String[] args) {
System.out.println(getShortName(“Sanjay”, “kumar”, “Chandel”));
System.out.println(getShortName(“sanjay”, “kumar”, “chandel”));
System.out.println(getShortName(“SANJAY”, “KUMAR”, “CHANDEL”));
}
}

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