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Rarely asked as it was introduced with Java 8.
 Q1201. What is DocLint in Java 8 ?Core Java
Ans. DocLint Provide a means to detect errors in Javadoc comments early in the development cycle and in a way that is easily linked back to the source code.

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   Like         Discuss         Correct / Improve     java   java 8   doclint   java8 features


Rarely asked as it was introduced with Java 8.
 Q1202. What are the errors identified by DocLint ?Core Java
Ans. Bad syntax, such as unescaped characters or unmatched parentheses

Bad HTML, such as invalid or missing tags or attributes

Bad references, such as referencing a non-existent type with @see

Accessibility errors, such as a missing summary or caption from a table

Missing info, such as an undocumented parameter

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   Like         Discuss         Correct / Improve     java   java8   java 8   doclint


 Q1203. What is the use of runnable interface if we can always create a new thread using Thread class ?Core Java
Ans. It's a choice to be made whether to use first approach ( Thread class ) or second approach ( runnable interface ) by the programmer. The second facility has been given for cases where your class is already extending some parent class and hence cannot extend another class ( for Thread ) as Java doesn't allow multiple inheritance.

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   Like         Discuss         Correct / Improve     java   threads   multithreading   runnable interface  concurrency


 Q1204. Why do we need Thread class even in case we execute thread using runnable interface ?Core Java
Ans. Thread class holds the definition of start method ( This is the method that starts execution of new thread and then calls run method within the scope of new thread ). Interfaces don't hold any definition and so does runnable. So it makes it necessary the usage of Thread class , whatever implementation you choose.

When your class extends the thread class, it carries the definition of start method from parent Thread class onto itself and hence new yourClass.start() helps starting a new thread and then executing run method in that new thread scope.

When you implement runnable interface , you are just making it sure to the JVM that you have implemented the required method ( run() ) which the Thread start method will look for upon executing start method.

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   Like         Discuss         Correct / Improve     java   threads   multithreading   runnable interface   thread class


 Q1205. Why Java uses Unicode System ?Core Java
Ans. Before Unicode there were many language / country standards like ASCII , ISO , KOI and BIG 5. In order to accommodate multiple language letters and to overcome problems with using different multiple standards , a new language standard was developed i.e unicode system.

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 Q1206. What is the difference between out.println(a+b); and out.println (a+" " +b); in Java? with a=2 and b=1Core Java
Ans. First will give the ouput as 3 and the second will give output as 2 1

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   Like         Discuss         Correct / Improve     java   system.out.println   coding


 Q1207. Which sorting algorithm is used by Collections.sort() in Java ?Core Java
Ans. The sorting algorithm is a modified mergesort. This algorithm offers guaranteed n log(n) performance.

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   Like         Discuss         Correct / Improve     java   algorithm   collections   collections.sort   sorting algorithm      expert

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 Q1208. What is the difference between Data Type and Data Structure ?Core Java
Ans. Data type: a set of values together with operations on that type
Data structure: a physical implementation of a data type

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 Q1209. How many elements will be there in TreeSet after the last line and Why ?

TreeSet set = new TreeSet();
set .add(new String("abc"));
set .add(new String("abc"));
Core Java
Ans. One.

As we haven't specified the type of TreeSet, it being evaluated with the first element insertion. Once it's identified that it's of type String and as no comparator has been defined, the comparison is done using the String compareTo method. String compareTo method compares the elements by the content / value.

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   Like         Discuss         Correct / Improve     java   set   treeset   string   compareto   coding   code


 Q1210. Which takes more memory - float or Float ?Core Java
Ans. float is a native data type whereas Float is a class. A Float object will always take more memory than float variable as there are metadata overheads with the objects.

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   Like         Discuss         Correct / Improve     java   data type   float     Asked in 3 Companies      basic        frequent


 Q1211. Difference between Stack and Heap memory ?Core Java
Ans. Stack memory areas is used to hold method and local variables while objects are always allocated memory in the heap. The heap memory is shared between multiple threads whereas Stack memory isn't.

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   Like         Discuss         Correct / Improve     java   memory management   stack memory   heap memory   difference between   ebay     Asked in 2 Companies      intermediate        frequent

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 Q1212. What is collision in hash collections ?Core Java
Ans. Collision is the situation when two different elements have the same Hash Code.

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   Like         Discuss         Correct / Improve     java   collections   collision   hashcode  hash code   hash collections   ebay     Asked in 1 Companies      intermediate        frequent


 Q1213. What will be the output ?Integer a = 10, b =10;Integer c = 10, d = 1000;System.out.println(a == b);System.out.println(c ==d);Core Java
Ans. truefalse

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   Like         Discuss         Correct / Improve     java   coding   equality   object equality


 Q1214. What is OutOfMemoryError in Java?Core Java
Ans. OutOfMemoryError in Java is a subclass of VirtualMachineError and is thrown by JVM when it runs out of heap memory.

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   Like         Discuss         Correct / Improve     outofmemoryerror   error   exceptions   jvm   java   heap memory   heap


 Q1215. Which access specifiers can be used with top level class ? a. public or default b. public or private c. public or protected d. protected or defaultCore Java
Ans. public or default

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   Like         Discuss         Correct / Improve     access specifier   oops   java   class     Asked in 2 Companies


 Q1216. Which of the following can be marked static ?

a. Methods , Variables and Initialization Blocks.
b. Methods , Variables , Initialization Blocks and Outer Classes and nested Classes.
c. Methods , Variables , Initialization Blocks and Outer Classes.
d. Methods , Variables , Initialization Blocks and nested Classes
Core Java
Ans. Methods , Variables , Initialization Blocks and nested Classes

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 Q1217. Which of the following collections stores its elements in insertion Order ?

a. HashMap
b. TreeMap
c. LinkedHashMap
d. LinkedMap
Core Java
Ans. LinkedHashMap

  Sample Code for LinkedHashMap

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   Like         Discuss         Correct / Improve     linkedhashmap   collections   java   map


 Q1218. In what order the elements of a HashSet are retrieved ?

a. Random Order
b. Insertion Order
c. Natural Sorting Order
d. Inverse Natural Sorting Order
Core Java
Ans. Random Order

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   Like         Discuss         Correct / Improve     collections   set   hashset   java

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 Q1219. Which interface does java.util.Hashtable implement ?

a. List
b. Set
c. Collection
d. Map
Core Java
Ans. Map

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   Like         Discuss         Correct / Improve     hashtable   java   collections


 Q1220. Which of the collections allows null as the key ?

a. HashTable
b. HashMap
c. TreeMap
d. LinkedHashMap
Core Java
Ans. HashMap

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   Like         Discuss         Correct / Improve     java   collections   map  hashtable     Asked in 2 Companies      basic        frequent


 Q1221. Which keyword is used to provide explicit access of a code block to single thread ?

a. Transient
b. Final
c. Explicit
d. Synchronized
Core Java
Ans. Synchronized

  Sample Code for Synchronized

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   Like         Discuss         Correct / Improve     java   threads   multithreading     Asked in 2 Companies      basic


 Q1222. Collections.sort can only be performed on ..

a. Set
b. List
c. Map
d. Any Collection implementation
Core Java
Ans. List

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 Q1223. Which of the following is false about main method ?

a. It should be declared public and static
b. it should have only 1 argument of type String array
c. We can override main method
d. We can overload main method
Core Java
Ans. We can override main method

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 Q1224. Which of the following is false about Constructors ?

a. Constructor can be overloaded
b. A no argument constructor is provided by the compiler if we declare only constructors with arguments.
c. Constructors shouldn't have any return types , not even void.
d. If super is not explicitly called, still super() is intrinsically added by the compiler.
Core Java
Ans. A no argument constructor is provided by the compiler if we declare only constructors with arguments.

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 Q1225. Strings in switch were introduced in Which Java version ? a. Java 5 b. Java 6 c. Java 7 d. JavaCore Java
Ans. Java 7

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 Q1226. Which of the following doesn't extend Collection interface ?

a. Set
b. List
c. Map
d. Queue
Core Java
Ans. Map

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 Q1227. Which of the following combination of keywords is illegal in Java ?

a. static and transient
b. transient and final
c. static and synchronized
d. abstract and final
Core Java
Ans. abstract and final

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 Q1228. Which of the following Java feature promotes Code Re usability ?

a. Abstraction
b. Encapsulation
c. Inheritance
d. Polymorphism
Core Java
Ans. Inheritance

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 Q1229. Which of the following Java feature promotes access protection or Hiding ?

a. Inheritance
b. Encapsulation
c. Abstraction
d. Composition
Core Java
Ans. Encapsulation

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Rarely asked as it was introduced with Java 8.
 Q1230. Which keyword specify that a variable is effectively final ? a. final b. No Keyword c. Both of the above d. None of the aboveCore Java
Ans. No Keyword

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   Like         Discuss         Correct / Improve     java   java 8   java8   final   effectively final        rare


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