问为什么传递对象在新关键字行之后不会被更改？

EN

public class Main {

public static void main(String[] args) {

    ObjectPassDemo ob1 = new ObjectPassDemo(100, 22);
    ObjectPassDemo ob2 = new ObjectPassDemo(100, 22);
    ObjectPassDemo ob3 = new ObjectPassDemo(-1, -1);
    ob2.change(ob2);
    System.out.println("In Main " + ob2.a + "," + ob2.b);

} }

class ObjectPassDemo {
public int a, b;

public ObjectPassDemo(int a, int b) {
    this.a = a;
    this.b = b;
}


void change(ObjectPassDemo o) {
    o.a=33;
    o.b=43;
    System.out.println("In method before constructor " + a + "," + b);
    o=new ObjectPassDemo(1000,2000);
    o.a=88;
    o.b = 888;
    System.out.println("In method after constructor " + a + "," + b);
}