java的参数传递与内存分配问题

public BirthDate(int d, int m, int y) {
day = d;
month = m;
year = y;
}

//省略get set

public void display() {
System.out.println
(day + " – " + month + " – " + year);
}
}

public class Test{
public static void main(String args[]){
Test test = new Test();
int date = 9;
BirthDate d1= new BirthDate(7,7,1970);
BirthDate d2= new BirthDate(1,1,2000);
test.change1(date);
test.change2(d1);
test.change3(d2);
System.out.println("date=" + date);
d1.display();
d2.display();
}

public void change1(int i){
i = 1234;
}

public void change2(BirthDate b) {
b = new BirthDate(22,2,2004);
}

public void change3(BirthDate b) {
b.setDay(22);
}
}