Example to clarify re-assignment of references

Meh.java

class Huh {
    public int huh;

    public Huh() {
        huh = 123;
    }
}

public class Meh {
    // Re-implement "toString()" for String
    private static String refString(String str) {
        return str.getClass().getName() + "@" +
            Integer.toHexString(str.hashCode());
    }

    public static void main(String[] args) {
        // Assign the reference to "the 1st String" to str1
        String str1 = "the 1st String";

        // Assign the current value / reference of str1 to str2
        String str2 = str1;

        System.out.println("[str1: " + refString(str1) + "] -> (\"" + str1 + "\")");
        System.out.println("[str2: " + refString(str2) + "] -> (\"" + str2 + "\")");

        /*
          Assign the reference to "the 2nd String" to str1

          this changes NEITHER the value / reference of str2
          NOR the object it refers to

          String objects in Java are *immutable*, which means
          whenever you make "changes" to a String, you are
          actually assigning the reference of a new instance
          to it instead of making changes to the current instance.

          It's the same story even when you are performing String
          concatenation with +=, by the way.
        */
        str1 = "the 2nd String";

        System.out.println("[str1: " + refString(str1) + "] -> (\"" + str1 + "\")");
        System.out.println("[str2: " + refString(str2) + "] -> (\"" + str2 + "\")");

        System.out.println();

        /*
          Another example with a simple class that has
          a *mutable* field
        */

        Huh huh1 = new Huh();
        Huh huh2 = huh1;

        System.out.println("[huh1: " + huh1 + "] -> (huh: " + huh1.huh + ")");
        System.out.println("[huh2: " + huh2 + "] -> (huh: " + huh2.huh + ")");

        /*
          This changes the field of a single instance
          that both huh1 and huh2 currently refers to
        */
        huh1.huh = 456;

        System.out.println("[huh1: " + huh1 + "] -> (huh: " + huh1.huh + ")");
        System.out.println("[huh2: " + huh2 + "] -> (huh: " + huh2.huh + ")");

        /*
          This creates a new instance and assign the
          reference to it to huh1. It changes NEITHER
          the value / reference of huh2 NOR the
          instance (i.e. its field) it refers to
        */
        huh1 = new Huh();

        System.out.println("[huh1: " + huh1 + "] -> (huh: " + huh1.huh + ")");
        System.out.println("[huh2: " + huh2 + "] -> (huh: " + huh2.huh + ")");
   }
}

Output:

[str1: java.lang.String@833d24ce] -> ("the 1st String")
[str2: java.lang.String@833d24ce] -> ("the 1st String")
[str1: java.lang.String@141d9cf8] -> ("the 2nd String")
[str2: java.lang.String@833d24ce] -> ("the 1st String")

[huh1: Huh@1055e4af] -> (huh: 123)
[huh2: Huh@1055e4af] -> (huh: 123)
[huh1: Huh@1055e4af] -> (huh: 456)
[huh2: Huh@1055e4af] -> (huh: 456)
[huh1: Huh@3caeaf62] -> (huh: 123)
[huh2: Huh@1055e4af] -> (huh: 456)