why this object still exists without it's composed class even tho it's com-positioned

i know that in composition the class composed inside, it's object should not exists outside of its class, but in the example below the Sword class is composed into the Unit class, and i can still create it's object independently without the unit class, like i did in main, how i can prevent for Sword object to exists independently?

public class Main {

public static void main(String[] args) {

    Sword sword = new Sword();

}
}

class Sword {
private int a;
}


class Unit {
private String s1;
private Sword s;

void setProperty(String s1, Sword s) {
    this.s1 = s1;
    this.s = s;
}

}