Use the double-check idiom with a volatile field.

[robxyy]

Effective Java #Item 71

[observeralone]

if(xxx!=null){
    return xxx;
}
//init xxx
if(xxx!=null){
   return xxx;
}

//init xxx
if(xxx!=null){
   return xxx;
}

if(xxx==null){
   //init xxx
   if(xxx==null){
      //init xxx  
       if(xxx==null){
          //init xxx
       }
   }
}
return xxx;

The first is more readable than the second, because the first is less nested.
At the same time they achieve the same purpose, so I don't understand why you modify this piece of code

[Oseenix]

Effective Java #Item 71

Thank you for your PR. It's not necessary to revert and rebase next time, so everyone can review on the changes. If any change required, just modify and push again. Finally, we use squash and merge make it looks like one commit.

[haoel]

@robxyy it's fine to push iteratively rather than push forcibly because we'd like to see the historical review comments and the changes. Don't worry about many commits after the merge, because we are going to do the squashing merge.

[observeralone]

@robxyy
Do you still want to change the code to push?
If not I will merge it.

[robxyy]

@Oseenix @haoel Thanks for the explanation, I'll pay attention next time.
@observeralone Please merge it. 🍺