通过反射获取字段名称是否应该避免进行昂贵的操作？

Question

I'm writing some validation code.

And don't want to declare much constants, so thinking about more dynamic way of how to get a name of properties of a class.

Ie

class User {
   String firstname;
   String lastname;

   getters/setters ....
}

Is the access via the

User.class.getDeclaredField("firstname").getName();

is an expensive operation and I rather go with constants or some other way?

Answer 1

If you use User.class.getDeclaredField("firstname").getName(); that will give as output firstname that is the same that the parameter.

long init = System.currentTimeMillis();

for(int i = 0; i < 1000000; ++i)
{
    Field[] fields = User.class.getDeclaredFields();

    for(Field field : fields)
    {
        field.getName();
    }
}

System.out.println(System.currentTimeMillis()-init);

That code takes only 500 ms, so in my opinion search between the fields isn't expensive

As suggested I added something in the loop for preventing the VM removing dead code

public static void main(String[] args) throws Exception {
long init = System.currentTimeMillis();
int count = 0;
for (int i = 0; i < 1000000; ++i) {
    Field[] fields = User.class.getDeclaredFields();
    for (Field field : fields) {
        if (field.getName().equals("firstname")) {
            count++;
        }
    }
}
System.out.println(count);
System.out.println(System.currentTimeMillis() - init);
}