Java Object Class

it is the base class of all the classes in java

 Methods in Java Object class

• hashCode:
  • the more unique the hashCode is the more efficient is the hash map/table
  • used to find the bucket in which an object goes into in a hash table.
  • more than one invocation of hashCode of the same object should return same Integer.
  • if two objects are equal according to equals method then their hashCode must be same.
• equals:
  • is used in hashMap when two objects have same hashCode.
  • if two objects are equal their hashCode must be same.
  • it should be
    • reflexive : x.equals(x)
    • symmetric:  x.equals(y) and y.equals(x)
    • transtive: x.equals(y) y.equals(z)   implies => x.equals(z) 
    • consitent: x.equals(y)  should allways return same value.
    • for null it should be false: x.equals(null)  false
  • the default behaviour of equals = “==” i.e is object comparision
• toString :
  • the default implementation is
  • classname  @ hex format of the hashCode.
  • its good to override toString .
  • also should be concise and informative.
• clone:
  • to clone the object .
  • x.clone() != x
  • x.clone().getClass() == x.getClass() Not mandatory *
  • x.clone().equals(x) Not mandatory *
  • alternative to clone is copy constructor