Question

What is the difference in bytecode between public attribute and private one with simple getter/setter in Java?

Answer 1

With public field you have:

aload_0
iconst_1
putfield        #1; //Field public
return

With private + set/get:

aload_0
iconst_1
putfield        #1; //Field private
return

public int getA();
  Code:
   0:   aload_0
   1:   getfield        #1; //Field private
   4:   ireturn

public void setA(int);
  Code:
   0:   aload_0
   1:   iload_1
   2:   putfield        #1; //Field private
   5:   return

So from the performance point of view private + set/get gives just unnecessary overhead. But it have an architecture profits and should be used by some conventions like JavaBeans.