Java Intern Strings Example

InternStringsExample.java

///usr/bin/env jbang "$0" "$@" ; exit $?

import java.util.List;
import java.util.LinkedList;

public class InternStringsExample {

    public static void main(String... args) throws Exception {
        List<String> strings = new LinkedList<String>();

        for(int i=0; i<1_000_000; i++)
            strings.add( "Visit Burgos!".intern() );
            //strings.add( new String("Visit Burgos") );
        
        Thread.currentThread().join();
    }
}

InternStringsExampleREADME.md

Intern Strings Example

With Intern Strings

jmap -histo:live pid | grep -i node
   1:       1000000       24000000  java.util.LinkedList$Node (java.base@17.0.1)

jmap -histo:live pid | grep -i string 
   5:          1645          39480  java.lang.String (java.base@17.0.1)

One million nodes are being allocated. Only few Strings are allocated (It should be just 1, but the JVM plays here too)

Without Intern Strings

jmap -histo:live pid | grep -i node  
   2:       1000000       24000000  java.util.LinkedList$Node (java.base@17.0.1)
jmap -histo:live pid | grep -i string
   1:       1001662       24039888  java.lang.String (java.base@17.0.1)
  49:             9            280  [Ljava.lang.String; (java.base@17.0.1) 

One million nodes are being allocated. One million String objects are being allocated. Your JVM may be runningn with -XX:+UseStringDeduplication, so underneath char[] will be reused.