Understanding the String Pool in Java

How Java Optimizes Memory and Performance Using String Interning

A string pool in Java is a special memory area in the heap where string literals are stored to optimize memory usage and improve performance through string interning.

Let’s try to understand this with the examples:

Example 1: Using the new String()

String a = new String(”Outcome School”);

String b = new String(”Outcome School”);

System . out . println(a == b); // false

new String(”Outcome School”) creates a new object in heap memory, not from the pool.

Example 2: Using String Literals, Without Using the new String()

String a = “Outcome School”;

String b = “Outcome School”;

System . out . println(a == b); // true

Here, both a and b point to the same object in the String Pool. No new object is created for b.

When you create a string literal (like “Outcome School”), Java first checks if an identical string already exists in the pool. If it does, Java returns a reference to the existing string rather than creating a new one. If not, it adds the new string to the pool.

Advantages:

• Reduces memory consumption by eliminating duplicate strings

• Improved performance for applications with many repeated strings

Use “Outcome School” instead of new String(”Outcome School”) whenever possible, it’s more efficient due to the String Pool.

Automatic Interning: String literals are automatically interned, but strings created with new String() are not unless explicitly interned.

Manual Interning: You can manually add strings to the pool using the intern() method:

String a = new String(”Outcome School”).intern(); // Now in String Pool

String b = “Outcome School”;

System . out . println(a == b); // true

Note: Kotlin’s string pool behavior is very similar to Java’s since Kotlin compiles to JVM bytecode and uses the same underlying string handling mechanisms.

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Thanks

Amit Shekhar

Founder, Outcome School