String splicing ""+1, String.valueOf(), str+"str" string splicing difference

analysis:

• ""+1
  is constant addition, the highest execution efficiency

• String s= str+"str"
  Since string is finally modified, str+"str" ​​is essentially carried out

   1.创建"str"新对象创建,
  
   2.str+"str"新对象的创建
   3.赋值给s
  

  Object-oriented programming, the most resource consuming is the creation and destruction of objects, so its stitching efficiency is the lowest

• String.valueOf()

Will directly call the type conversion method, the efficiency is in the middle