引用计数如何工作？

Question

假设一个测试场景

Employee *aObj = [[Employee alloc]init];
NSLog(@"Retain count is1: %ld", CFGetRetainCount((__bridge CFTypeRef)aObj));
Employee *bObj = aObj;
NSLog(@"Retain count is2: %ld", CFGetRetainCount((__bridgCFTypeRef)bObj));
Employee *cObj = bObj; 

NSLog(@"Retain count is3: %ld", CFGetRetainCount((__bridge CFTypeRef)cObj));

 Then output is :
 TestMemory[1949:62438] Retain count is1: 1
 TestMemory[1949:62438] Retain count is2: 2
 TestMemory[1949:62438] Retain count is3: 3


Employee *aObj = [[Employee alloc]init];
Employee *bObj = aObj;
Employee *cObj = bObj;

NSLog(@"Retain count is1: %ld", CFGetRetainCount((__bridge CFTypeRef)aObj));
NSLog(@"Retain count is2: %ld", CFGetRetainCount((__bridge CFTypeRef)bObj));
NSLog(@"Retain count is3: %ld", CFGetRetainCount((__bridge CFTypeRef)cObj));

 Then output is :
 TestMemory[1949:62438] Retain count is1: 3
 TestMemory[1949:62438] Retain count is2: 3
 TestMemory[1949:62438] Retain count is3: 3

所以我得到两个不同的输出，使用相同的代码。谁能解释为什么会这样？请帮助我。