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Sudhakar V
Sudhakar V

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Strings in Java

In Java, strings are objects that represent sequences of characters. The Java language provides special support for strings through the String class in the java.lang package.

Creating Strings

There are two main ways to create strings in Java:

  1. String literals (stored in string pool): 
   String str1 = "Hello World";
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  1. Using new keyword (creates new object in heap memory): 
   String str2 = new String("Hello World");
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Important String Methods

Java's String class provides many useful methods:

Basic Methods 

String s = "Hello";

int length = s.length();          // 5
char c = s.charAt(1);             // 'e'
String sub = s.substring(1, 3);   // "el"
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Comparison Methods 

String s1 = "Hello";
String s2 = "hello";

boolean equal = s1.equals(s2);            // false
boolean equalIgnoreCase = s1.equalsIgnoreCase(s2);  // true
int compare = s1.compareTo(s2);           // negative number (H < h)
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Searching Methods 

String s = "Hello World";

int index = s.indexOf('o');       // 4
int lastIndex = s.lastIndexOf('o'); // 7
boolean contains = s.contains("World"); // true
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Modification Methods 

String s = "  Hello World  ";

String trimmed = s.trim();         // "Hello World"
String replaced = s.replace('l', 'L'); // "  HeLLo WorLd  "
String upper = s.toUpperCase();     // "  HELLO WORLD  "
String lower = s.toLowerCase();     // "  hello world  "
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Splitting and Joining 

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

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

Strings in Java are immutable - once created, their values cannot be changed. Operations that appear to modify strings actually create new string objects.

String s = "hello";
s.concat(" world");  // Doesn't change s
s = s.concat(" world");  // Now s refers to new string "hello world"
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StringBuilder and StringBuffer

For mutable sequences of characters, Java provides:

  • StringBuilder (faster, not thread-safe)
  • StringBuffer (thread-safe, slower) 
StringBuilder sb = new StringBuilder("Hello");
sb.append(" World");  // Modifies the existing object
String result = sb.toString();  // "Hello World"
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String Formatting

Java provides several ways to format strings:

String formatted = String.format("Name: %s, Age: %d", "Alice", 25);
// "Name: Alice, Age: 25"
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Important Notes

  • Use equals() to compare string contents, not == (which compares references)
  • Strings are stored in UTF-16 encoding
  • Java performs string interning for literals to save memory
  • For heavy string manipulation, prefer StringBuilder over concatenation with +

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