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Rarely asked Java Interview Questions and Answers - 72 question(s) found - Order By Newest

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 Q1. What are the common uses of "this" keyword in java ?Core Java
Anonymous
Ans. "this" keyword is a reference to the current object and can be used for following -

1. Passing itself to another method.

2. Referring to the instance variable when local variable has the same name.

3. Calling another constructor in constructor chaining.

  Sample Code for this keyword

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 Q2. Can we use both "this()" and "super()" in a constructor ?Core Java
Anonymous
Ans. No, because both this and super should be the first statement.

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 Q3. How does making string as immutable helps with securing information ? How does String Pool pose a security threat ?Core Java2017-06-22 11:32:57

Ans. String is widely used as parameter for many java classes, e.g. network connection, opening files, etc. Making it mutable might possess threats due to interception by the other code segment or hacker over internet.

Once a String constant is created in Java , it stays in string constant pool until garbage collected and hence stays there much longer than what's needed. Any unauthorized access to string Pool pose a threat of exposing these values.


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 Q4. Can we declare static variables as transient ?Core Java2017-01-12 11:12:48

Ans. It's weird that compiler doesn't complain if we declare transient with static variable because it makes no sense. At least a warning message saying "transient is useless in this situation" would have helped with code cleaning.

Static variables are never serialized and transient is an indication that the specified variable shouldn't be serialized so its kind of double enforcement not to serialize.

It could be that as it makes no different to the variable behavior and hence using both keywords with a variable are permitted.

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 Q5. What are the Wrapper classes available for primitive types ?Core Java
Anonymous
Ans. boolean - java.lang.Boolean
byte - java.lang.Byte
char - java.lang.Character
double - java.lang.Double
float - java.lang.Float
int - java.lang.Integer
long - java.lang.Long
short - java.lang.Short
void - java.lang.Void

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 Q6. What are concepts introduced with Java 5 ?Core Java
Anonymous
Ans. Generics , Enums , Autoboxing , Annotations and Static Import.

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 Q7. Does Constructor creates the object ?Core Java
Anonymous
Ans. New operator in Java creates objects. Constructor is the later step in object creation. Constructor's job is to initialize the members after the object has reserved memory for itself.

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 Q8. Which String class does not override the equals() and hashCode() methods, inheriting them directly from class Object?Core Java
Anonymous
Ans. java.lang.StringBuffer.

  Sample Code for StringBuffer

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 Q9. Can we serialize static variables ?Core Java
Anonymous
Ans. No. Only Object and its members are serialized. Static variables are shared variables and doesn't correspond to a specific object.

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 Q10. Can constructors be synchronized in Java ?Core Java
Anonymous
Ans. No. Java doesn't allow multi thread access to object constructors so synchronization is not even needed.

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Usually asked only to fresh graduates.
 Q11. What is the difference between time slicing and preemptive scheduling ?Operating System
Anonymous
Ans. In preemptive scheduling, highest priority task continues execution till it enters a not running state or a higher priority task comes into existence. In time slicing, the task continues its execution for a predefined period of time and reenters the pool of ready tasks.

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 Q12. Are constructors inherited? Can a subclass call the parent's class constructor? When?Core Java
Anonymous
Ans. You cannot inherit a constructor. That is, you cannot create a instance of a subclass using a constructor of one of it's superclasses. One of the main reasons is because you probably don't want to override the superclasses constructor, which would be possible if they were inherited. By giving the developer the ability to override a superclasses constructor you would erode the encapsulation abilities of the language.

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 Q13. In which cases , moving methods to utility class could be useful ?Core Java

Ans. It could be worthy to move a method to util class if the method needs to be shared, doesn't require polymorphic behavior and need not be overridden in special cases.

Don't belong to one group through is-a relationship ( You can share through parent class method )

Don't implement a specific interface ( java 8 default methods )

Doesn't involve complex computing as you will be loosing the benefit of object state with just static method.

Doesn't require polymorphic behavior as static methods don't participate in runtime polymorphism.

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   Like      Discuss      Correct / Improve     utility classes   util classes   static methods   application design        rare


 Q14. Can you write a "Hello World" program without using any ";" within it?Core Java2016-12-13 08:26:23

Ans. Yes, That is possible

class A {
public static void main(String args[]){
if(System.out.printf("Hello World")==null){}
}
}

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 Q15.  What is the role of JSON.stringify ?Json
Anonymous
Ans.  JSON.stringify() turns an object into a JSON text and stores that JSON text in a string. 

So If we stringfy above notation , it will become

{"name":"xyz","gender":"male";"age":30}

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 Q16. What is URL?
Java EE
Anonymous
Ans. URL is Uniform Resource Locator which is representation of HTTP address.

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 Q17. Can I import same package/class twice? Will the JVM load the package twice at runtime?Core Java
Anonymous
Ans. One can import the same package or same class multiple times. Neither compiler nor JVM complains wil complain about it. And the JVM will internally load the class only once no matter how many times you import the same class.

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 Q18. Difference between boolean and Boolean ?Core Java
Anonymous
Ans. boolean is a primitive type whereas Boolean is a class.

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 Q19. Will this code give error if i try to add two heterogeneous elements in the arraylist. ? and Why ?

List list1 = new ArrayList<>();
list1.add(5);
list1.add("5");
Admin
info@buggybread.com
Ans. If we don't declare the list to be of specific type, it treats it as list of objects.

int 1 is auto boxed to Integer and "1" is String and hence both are objects.

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 Q20. What is servlet Chaining ?Java EE
Anonymous
Ans. Multiple servlets serving the request in chain.

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 Q21. Which interface does java.util.Hashtable implement?Core Java
Anonymous
Ans. Java.util.Map

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 Q22. Difference between long.Class and Long.TYPE ?
Anonymous
Ans. They both represent the long primitive type. They are exactly the same.

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 Q23. What are transient variables in java?Core Java
Anonymous
Ans. Transient variables are variable that cannot be serialized.

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 Q24. Which memory segment loads the java code ?Core Java
Anonymous
Ans. Code segment.

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 Q25. Can a lock be acquired on a class ?
Anonymous
Ans. Yes, a lock can be acquired on a class. This lock is acquired on the class's Class object.

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 Q26. Will Compiler creates a default no argument constructor if we specify only multi argument constructor ?
Anonymous
Ans. No, Compiler will create default constructor only if we don't specify any constructor.

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 Q27. Can we declare an abstract method private ?
Anonymous
Ans. No Abstract methods can only be declared protected or public.

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 Q28. What is suspend() method used for ?
Admin
info@buggybread.com
Ans. suspend() method is used to suspend the execution of a thread for a period of time. We can then restart the thread by using resume() method.

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Usually asked only to fresh graduates.
 Q29. Difference between suspend() and stop() ?
admin
info@buggybread.com
Ans. Suspend method is used to suspend thread which can be restarted by using resume() method. stop() is used to stop the thread, it cannot be restarted again.

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 Q30. What is the difference between System.console.write and System.out.println ?
Admin
info@buggybread.com
Ans. System.console() returns null if your application is not run in a terminal (though you can handle this in your application)System.console() provides methods for reading password without echoing charactersSystem.out and System.err use the default platform encoding, while the Console class output methods use the console encoding

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 Q31. Which load testing tools have you used ?
Anonymous
Ans. Rational Robot, JMeter, LoadRunner

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 Q32. What data type Variable can be used in a switch statement ?Core Java
Admin
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Ans. Variables used in a switch statement can only be a byte, short, int, or char ( and String with Java 7 and above )

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 Q33. What is the Locale class?
Admin
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Ans. The Locale class is used to tailor program output to the conventions of a particular geographic, political, or cultural region

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 Q34. What is Externalizable interface?Core Java
Admin
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Ans. Externalizable is an interface which contains two methods readExternal and writeExternal. These methods give you a control over the serialization mechanism.

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  Q35. Write a Program to check if 2 strings are Anagrams ?Core Java2016-11-30 20:52:37

Ans. public void checkIfAnagram(String str1,String str2){
boolean anagram = true;
for(char c:str1.toCharArray()){
if(!str2.contains(String.valueOf(c))){
System.out.println("Strings are Anagrams");
anagram = false;
}

if(anagram == true){
System.out.println("Strings are not Anagrams");
}
}
}

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 Q36. Difference between PATH and CLASSPATH ?Operating System
Admin
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Ans. PATH is the variable that holds the directories for the OS to look for executables. CLASSPATH is the variable that holds the directories for JVM to look for .class files ( Byte Code ).

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 Q37. What is a ConcurrentHashMap ?Core Java
Admin
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Ans. ConcurrentHashMap is a hashMap that allows concurrent modifications from multiple threads as there can be multiple locks on the same hashmap.

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Rarely asked as default methods have been introduced with Java 8.
 Q38. Can we have a default method without a Body ?Core Java
Admin
info@buggybread.com
Ans. No. Compiler will give error.

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 Q39. What is Closeable ?Core Java
Admin
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Ans. A Closeable is an interface which is a source or destination of data that can be closed.

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 Q40. Name few Locale classes and interfaces ?
Admin
info@buggybread.com
Ans. http://www.buggybread.com/2015/01/java-locale-classes-and-interfaces.html

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