What is the purpose of String Pool in Java?

String Pool in Java is necessary for:

• Memory saving: Prevents creating duplicate string literals. If a string with the same value already exists in the pool, a reference to it is used.
• Performance optimization: Comparing string literals (==) becomes faster because references are compared, not the content of the strings.

When creating string literals (String s = "hello";), the JVM first checks the String Pool. If "hello" already exists, s references the existing object. If not, a new "hello" object is created in the pool, and s references it.

Using the constructor new String("hello") always creates a new String object in the heap, regardless of the String Pool. To add it to the pool, the intern() method must be called.

// Example of String Pool operation

String s1 = "hello"; // Checks String Pool, creates if necessary, references the pool
String s2 = "hello"; // Checks String Pool, finds existing, also references the pool

System.out.println(s1 == s2); // true - references are the same

String s3 = new String("hello"); // Creates a new object in the heap

System.out.println(s1 == s3); // false - references are different

String s4 = s3.intern(); // Checks String Pool for s3's content.
                         // Since "hello" already exists in the pool (from s1/s2),
                         // s4 references the object in the pool.

System.out.println(s1 == s4); // true - s1 and s4 reference the same object in the pool