Defensive copy from Effective Java

Question

I am reading \"Effective Java\" by Joshua Bloch, item 39 make defensive copy, and I have some questions. I always use the following construct:

MyObject.getSo         


        

Answer 1

call getSomeRef() two times and compare there reference if they are different then function is returning the copy else it is returning the same instance.

if(MyObject.getSomeRef() == MyObject.getSomeRef()){
     // same instance
}else{
     // copied instance
}