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Core Java - Interview Questions and Answers for 'Object class' - 5 question(s) found - Order By Newest

Very frequently asked. Among first few questions in almost all interviews. Among Top 5 frequently asked questions. Frequently asked in Indian service companies (HCL,TCS,Infosys,Capgemini etc based on multiple feedback ) and Epam Systems
  Q1. Difference between == and .equals() ?Core Java
Ans. "equals" is the method of object class which is supposed to be overridden to check object equality, whereas "==" operator evaluate to see if the object handlers on the left and right are pointing to the same object in memory.

x.equals(y) means the references x and y are holding objects that are equal. x==y means that the references x and y have same object.

Sample code:

String x = new String("str");
String y = new String("str");

System.out.println(x == y); // prints false
System.out.println(x.equals(y)); // prints true

  Sample Code for equals

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   Like         Discuss         Correct / Improve     java   string comparison   string   object class   ==    equals   object equality  operator   == vs equals   equals vs ==     Asked in 294 Companies      basic        frequent

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Frequently asked. Favorite question in Walk in Drive of many Indian service companies.
  Q2. What are the methods of Object Class ?Core Java
Ans. clone() - Creates and returns a copy of this object.

equals() - Indicates whether some other object is "equal to" this one.

finalize() - Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.

getClass() - Returns the runtime class of an object.

hashCode() - Returns a hash code value for the object.

toString() - Returns a string representation of the object.

notify(), notifyAll(), and wait() - Play a part in synchronizing the activities of independently running threads in a program.

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   Like         Discuss         Correct / Improve     java   oops   object class     Asked in 16 Companies      basic        frequent

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 Q3. Which String class does not override the equals() and hashCode() methods, inheriting them directly from class Object?Core Java
Ans. java.lang.StringBuffer.

  Sample Code for StringBuffer

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   Like         Discuss         Correct / Improve     java   object class   stringbuffer      expert        rare


 Q4. What is the use of Object class ?Core Java
Ans. 1. Default definition for some of the methods , like equals, hashcode etc that gets carried to all objects even if you don't define anything. But that default definition is kind of like assigning 0 to integer, it just provide a safe state , nothing much for comparison.

2. Places where you have no idea about what object you may receive and just want to perform out of 8 basic methods of object class, something like printing their string representation ( defined by their toString method ), or equality ( using their equals method )

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   Like         Discuss         Correct / Improve     object class


 Q5. Can we override wait() or notify() methods?Core Java
Ans. wait and notify are declared final in object class and hence cannot be overridden.

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   Like         Discuss         Correct / Improve     object class methods  wait  notify


 Q6. Which of following is not the method of object class ?Core Java
a. run
b. notify
c. wait
d. clone

Ans.a. run


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