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 createdhello worldgc 代码如上所示， 求解释为什么hello world会在gc之前输出？？