String_Pool.md

String Pool in Java

What is String Pool?

String Pool in Java is a special memory region in the heap that stores string literals. When a string literal is created, Java checks whether an identical string already exists in the pool. If it does, a reference to the existing string is returned instead of creating a new object, thereby optimizing memory usage.

How String Pool Works

1. When a string literal is created, Java checks the String Pool for an existing instance.
2. If the string is found, the existing reference is returned.
3. If not, a new string object is created and added to the pool.
4. Strings created using the new keyword do not use the pool by default, but they can be added manually using the intern() method.

Example

public class StringPoolExample {
    public static void main(String[] args) {
        String s1 = "Hello";
        String s2 = "Hello";
        String s3 = new String("Hello");
        String s4 = s3.intern();

        System.out.println(s1 == s2); // true (same reference from pool)
        System.out.println(s1 == s3); // false (different objects)
        System.out.println(s1 == s4); // true (s4 is interned, points to pool)
    }
}

Benefits of String Pool

• Memory Efficiency: Reduces memory consumption by reusing immutable string objects.
• Performance Optimization: Reduces the number of objects created, improving efficiency.

When to Use intern()

If a string is created using new String(), it resides in the heap and not in the pool. To store it in the pool and get its reference, use intern():

String s = new String("Java").intern();

Conclusion

The String Pool mechanism in Java helps optimize memory usage by reusing immutable string literals. Understanding how it works is essential for efficient Java programming.