Java String intern()

The syntax of the string intern() method is:

string.intern()

Here, string is an object of the String class.

intern() Parameters

The intern() method does not take any parameters.

intern() Return Value

• returns a canonical representation of the string

What is Java String Interning?

The String interning ensures that all strings having the same contents use the same memory.

Suppose, we these two strings:

String str1 = "xyz";
String str2 = "xyz";

Since both str1 and str2 have the same contents, both these strings will share the same memory. Java automatically interns the string literals.

However, if you create strings with using the new keyword, these strings won't share the same memory. For example,

class Main {
  public static void main(String[] args) {

    String str1 = new String("xyz");
    String str2 = new String("xyz");


    System.out.println(str1 == str2); // false

  }
}

As you can see from this example, both str1 and str2 have the same content. However, they are not equal because they don't share the same memory.

In this case, you can manually use the intern() method so that the same memory is used for strings having the same content.

Example: Java String intern()

class Main {
  public static void main(String[] args) {

    String str1 = new String("xyz");
    String str2 = new String("xyz");

    // str1 and str2 doesn't share the same memory pool
    System.out.println(str1 == str2); // false

    // using the intern() method
    // now both str1 and str2 share the same memory pool
    str1 = str1.intern();
    str2 = str2.intern();

    System.out.println(str1 == str2); // true
  }
}

As you can see, both str1 and str2 have the same content, but they are not equal initially.

We then use the intern() method so that str1 and str2 use the same memory pool. After we use intern(), str1 and str2 are equal.