Understanding the String Constant Pool in Java

What is the String Constant Pool?

The String Constant Pool, also known as the String Intern Pool, is a special storage area in the Java heap where String literals are stored. This mechanism helps in saving memory and improving performance when dealing with String objects.

How the String Constant Pool Works

• When a String literal is created (e.g., String s = "Hello";), the JVM checks if that literal already exists in the pool.
• If it exists, a reference to the existing String is returned.
• If it does not exist, the new String literal is added to the pool.

Example of String Constant Pool

        String s1 = "Hello"; // Creates a String in the pool
        String s2 = "Hello"; // References the same String in the pool
        System.out.println(s1 == s2); // true, both reference the same object

Using the new Keyword

When the new keyword is used to create a String, it always creates a new instance of the String object, regardless of whether the same String already exists in the pool.

Example with new Keyword

        String s3 = new String("Hello"); // Creates a new String object in heap memory
        System.out.println(s1 == s3); // false, references different objects

Conclusion

The String Constant Pool is an efficient way to manage String literals in Java, allowing reuse of String objects and saving memory. However, using the new keyword bypasses this optimization, leading to the creation of new String objects even if identical literals exist in the pool. Understanding this distinction is key for effective memory management in Java applications.