What is the purpose of String intern() method in Java?

String is a class that stores character sequences in Java. It belongs to the java.lang package. Once String objects are created, they cannot be modified (immutable).

Storage

All String objects are stored in a separate memory location in the heap area, called the String Constant Pool.

Whenever a string value is defined, the JVM creates a string object with the given value in the string constant pool. So if you run the above program, two string values ​​will be created in the string constant pool.

intern() method

This method returns the value of the current string from the pool of unique string values. Whenever you call this method on a particular String, it will be returned if the String constant pool already contains a String that is equal to it (according to the equals method of the Object class). If not, the current string is added to the string constant pool and a reference to it is returned.

That is, if you call this method on two strings with the same content, they are guaranteed to share the same memory.

This method can easily reduce the memory occupied when multiple duplicate values ​​appear.

Example

Below we will create two strings with the same content (using the new keyword) and compare them using the "==" operator. Although both objects have the same value, since they do not reference the same object (memory), the result will be false.

public class InternExample {
   public static void main(String args[]) {
      String str1 = new String("Hello");
      str1 = str1.intern();
      String str2 = "Hello";
      str2 = str2.intern();
      System.out.println(str1.equals(str2));
   }
}

Output

false

However, if you call the intern method before comparing the two objects because it ensures that both objects share the same memory (if they have the same content), then the result will be true.

public class InternExample {
   public static void main(String args[]) {
      String str1 = new String("Hello");
      str1 = str1.intern();
      String str2 = new String("Hello");
      str2 = str2.intern();
      System.out.println(str1==str2);
   }
}

Output

true

The above is the detailed content of What is the purpose of String intern() method in Java?. For more information, please follow other related articles on the PHP Chinese website!