一脸懵逼

public class Test {
  public static void a(Integer i, B b) {
  i = 1;
  b.setNum(2);
}

public static void main(String[] args) {
  Integer i = new Integer(0);
  B b = new B();
  a(i, b);
  System.out.println(i);
  System.out.println(b.getNum());
}
  }

  class B {
private Integer num;

public Integer getNum() {
  return num;
}

public void setNum(Integer num) {
  this.num = num;
}
  }
​

结果：
0
2

为什么结果不是：1,2 呢