How to improve java code??

Question

Java

At the interview, they asked me to improve the code, but I could not answer with advice on improvement ((
Tell me, how could I answer ??

Spring bes="";
for(int i=0;i<10;i++){
bes+="_";
}

Answer 1

Use the StringBuilder class, now with each operation you allocate memory for a new string and copy the data there. bes+="_";