关于System.gc()的执行？

Question

package FinalizeTest;

public class Person {

    

    public Person(){

        System.out.println("person created");

    }

    @Override

    protected void finalize() throws Throwable {

        // TODO Auto-generated method stub

        System.out.println("gc ");

        throw new Exception("no effect");

    }

}

package FinalizeTest;

public class MainTest {

    /**

     * @param args

     */

    public static void main(String[] args) {

        // TODO Auto-generated method stub

        Person per = new Person();

        per = null;

        System.gc();

        System.out.println("hello world");

    }

}

输出为

person created

hello world

gc 

代码如上所示， 求解释为什么hello world会在gc之前输出？？