.intern()

The .intern() method creates an exact copy of a string located in the heap memory and stores it in the string constant pool. With this method, it is possible to optimize memory usage in a Java program by reusing identical string objects.

However, if in the string constant pool exists another string with the same value, a new object won’t be created and the new reference will point to the other string.

Syntax

There are two ways to invoke the intern() method. The first one is used with the new keyword. The second one is directly used on a string literal.

// Using new keyword
String <variable name> = new String(<"string value">).intern();

// Used on a string literal
<String name>.intern();

Example

String str1 = "hello";
String str2 = new String("hello");
String str3 = str2.intern();

System.out.println(str1 == str2);
System.out.println(str1 == str3);

The output of the code above will be:

false
true

In this example above, there are three string objects: str1, str2, and str3. str1 is created using the string literal syntax, while str2 is created using the new keyword to create a new instance of the string class. The intern() method is called on str2, which returns a reference to the interned string. The == operator is used to compare the references of str1 and str2, which returns false because they are different objects with different memory addresses. However, when we compare str1 and str3, which are both interned string objects, the == operator returns true because they are the same object with the same memory address.