Differences Between Heap Memory and String Constant Pool in Java

The Heap Memory and String Constant Pool are two different memory locations in Java where objects are stored during the execution of programs. Both memory areas are managed by the Java Virtual Machine.

In this article, we are going to discuss the difference between Heap Memory and String Constant Pool in Java.

Heap Memory

Heap memory is a runtime data area from which memory for all class instances and arrays is allocated. It is the main memory area used for dynamic memory allocation in Java.

Example

Creating strings with the new keyword always allocates new memory in the heap. In this example, the str1 refers to a new object in the heap. And, the str2 also refers to another new object in the heap, even though the text is the same.

public class Example {
   public static void main(String[] args) {
      String str1 = new String("Tutorialspoint");
      String str2 = new String("Tutorialspoint");
      System.out.print("Is both strings equal: ");
      System.out.println(str1 == str2); 
   }
}

The above Java program will produce the following output:

Is both strings equal: false

String Constant Pool

Within the heap, the String constant pool is located. It stores unique string literals. Whenever a new string variable is created, the JVM will match the specified value with the values within the pool.

In case of a match, instead of creating a new string (new memory location) JVM will use the existing value.

Example

String literals with the same value share the same memory reference in the String Constant Pool. In the following example, both str1 and str2 are assigned the same string literal. Hence, the JVM will reuse the reference instead of creating a new one.

public class Example {
   public static void main(String[] args) {
      String str1 = "Tutorialspoint";
      String str2 = "Tutorialspoint";
      System.out.print("Is both strings equal: ");
      System.out.println(str1 == str2); 
   }
}

When you run the above code, it will give the following result:

Is both strings equal: true

Heap Memory VS String Constant Pool

In the table given below, the difference between heap memory and string constant pool is listed: