java - Grabage コレクションの対象となるオブジェクト

Question

interface Animal { void makeNoise(); } 

class Horse implements Animal {
  Long weight = 1200L; 
  public void makeNoise() { System.out.println("whinny"); } 
} 

public class Icelandic extends Horse {

  public void makeNoise() { System.out.println("vinny"); } 
  public static void main(String[] args) { 
    Icelandic i1 = new Icelandic(); 
    Icelandic i2 = new Icelandic(); 
    Icelandic i3 = new Icelandic(); 
    i3 = i1; 
    i1 = i2;
    i2 = null;
    i3 = i1; 
    //<-- HERE
  } 
} 

HERE に達したとき、いくつのオブジェクトがgarbage collector? なぜ？