Q7: Why are Java Strings immutable and how does the String Constant Pool work?
Strings in Java are final and immutable for Security (db connections, network parameters), Thread-Safety (shared without synchronization), and Caching.
The String Constant Pool (SCP) is a special heap area. String literals are stored here and shared across the JVM to reduce duplicate memory footprint.
String Literal vs New Instance Allocation
String s1 = "Java"; // Stored in String Pool
String s2 = "Java"; // Reuses pooled instance
String s3 = new String("Java"); // Explicitly creates new Heap object
System.out.println(s1 == s2); // true (same reference)
System.out.println(s1 == s3); // false (different heap memory addresses)💡 Literals reuse SCP instances; string construction via new allocates distinct heap instances.
Key Takeaways
- Immutability enables safe sharing, hash code caching, and thread safety.
- String literals are stored in the String Constant Pool inside heap memory.
Knowledge Check
Where is the String Constant Pool located in modern Java architectures (Java 7+)?