Why the size of empty class is 1 byte but the size of empty structure is 0 bytes

Answer 1

because every class extends from Object, so they have ther methods, like "toString()" , or "equals(obj)"

Answer 2

sorry not understood.Could u please elaborate

Answer 3

A class is instantiated only when you create a new object to it(even though the class is empty). There by when a new object is created to the empty class the compiler assigns address for that, address stored in memory occupies 1 byte.
Therefore the sizeof an empty class will be atleast 1 byte