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Basic Core Java MCQ

1. What is the difference between HashMap and HashTable?

HashMap is not Synchronized

Both are Synchronized

None of them

HashTable is not Synchronized

Answer

Correct Answer: HashMap is not Synchronized

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2. Which of the following statements is false about objects?

Objects can access both static and instance data

An instance of a class is an object

Objects do not permit encapsulation

Answer

Correct Answer: Objects do not permit encapsulation

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3. True or False: All classes that can be instantiated must implement the class Object

False

It depends on the class

True

Answer

Correct Answer: False

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4. java.lang.Object is the super class of all the interfaces in java

true

false

Answer

Correct Answer: false

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5. A RuntimeException is...

either, depending on what it extends

An Unchecked Exception

A Checked Exception

Answer

Correct Answer: A Checked Exception

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6. what is order of preference in method overloading

Boxing, Widening, Varargs

Varargs, Boxing, Widening

Widening, Boxing, Varargs

All have equal preference

Answer

Correct Answer: Widening, Boxing, Varargs

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7. Given a class containing the following pieces of code: public static <T> List getList() { return new ArrayList<T>(); } // ... List<?> list = new ArrayList<Integer>(); Adding which of the following lines would cause the class to not compile?

List<Integer> list2 = list;

list = new ArrayList<String>();

list = getList();

All of these compile

List<Integer> list2 = getList();

Answer

Correct Answer: List<Integer> list2 = list;

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8. how java is platform independent?

it has JDK for different platforms

it has JVM for different platforms

it has JRE for different platforms

Answer

Correct Answer: it has JVM for different platforms

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9. The JVM allows programmers to manipulate the registers of the underlying system

False

True

Answer

Correct Answer: False

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10. which of the following is correct syntax of varargs

public void display(String message, String... values)

public void display(String... values, String.. messages)

public void display(String... values, String message)

Answer

Correct Answer: public void display(String message, String... values)

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11. What is a LinkedHashSet?

A hash set which preserves the order in which objects were inserted.

A superclass of the HashSet object.

A hash set with the performance of a linked list.

A hash set which can easily be converted into a linked list.

Answer

Correct Answer: A hash set which preserves the order in which objects were inserted.

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12. which is the default package in every java program?

java.system.*

java.util.*

java.lang.*

java.io.*

java.lang.Object.*

Answer

Correct Answer: java.lang.*

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13. What is @Override annotation used for?

It just makes your code easier to read

It makes method virtual

It makes compiler check that method is really overridden

Answer

Correct Answer: It makes compiler check that method is really overridden

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14. The data members of interface in java are:

protected final

private static

public static final

private static final

static final

Answer

Correct Answer: public static final

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15. ConcurrentModificationException will be thrown only when an object is concurrently modified.

False

True

Answer

Correct Answer: False

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16. Which one is most suitable to implement an LRU cache?

ConcurrentHashMap

WeakHashMap

TreeMap

LinkedHashMap

Answer

Correct Answer: LinkedHashMap

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17. Do Hashtable allow null keys and null values?

False

True

Answer

Correct Answer: False

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18. HashMap is non-synchronized ?

False

True

Answer

Correct Answer: True

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19. HTML based Java Documentary help can be accessed using.. ?

javadoc

javamanual

none of these

javahelp

all of the above

Answer

Correct Answer: javadoc

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20. ConcurrentModificationException extends .......

ArthematicException

RuntimeException

ArrayIndexOutOfBoundsException

ClassCastException

Answer

Correct Answer: RuntimeException

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21. What is super class of all classes in Java?

Object class

Abstract Class

Util class

Collections

Answer

Correct Answer: Object class

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22. A Guarded Block is a concurrency idiom in which:

All statements in a block of code are guaranteed to be executed completely, or not at all

A block of code will only ever be executed in synchronized mode

A block of code is protected by an intrinsic lock obtained from a specific Object or Class

A condition is polled before the execution of a code block can proceed

Answer

Correct Answer: A condition is polled before the execution of a code block can proceed

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23. What will be the output of this code? class Main { static abstract class Base { protected Base() { init(); } abstract void init(); } static class Child extends Base { private final int value; public Child() { value = 5; } @Override public void init() { System.out.println("value = " + value); } } public static void main(String[] args) { Child c = new Child(); } }

Compilation error

Runtime exception

value = 0

value = 5

Answer

Correct Answer: value = 0

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24. Given a class containing the following pieces of code: ---------------------- public static <T> List getList() { return new ArrayList<T>(); } // ... List<?> list = new ArrayList<Integer>(); ---------------------- Adding which of the following lines would cause the class to not compile?

List<Integer> list2 = list;

All of these compile

list = getList();

list = new ArrayList<String>();

List<Integer> list2 = getList();

Answer

Correct Answer: List<Integer> list2 = list;

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25. Livelock describes a situation in which two or more threads block each other, because:

Each are waiting on the other thread(s) before acting, such that no thread takes action

A call to Thread.sleep() has suspended the action on all threads in the VM

Their actions are also responses to the actions of others, such that all are too busy to respond

They are unable to gain access to shared resources, and cannot make any progress

Answer

Correct Answer: Their actions are also responses to the actions of others, such that all are too busy to respond

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26. @Inject annotation belongs to

JSR-250

JSR-230

JSR-320

JSR-330

@Inject is not core Java annotation

Answer

Correct Answer: JSR-330

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27. Which of the following is true about the Cloneable interface?

Creates an exact copy of the implementing class by calling its constructor.

It provides a clone method that must be implemented.

Is just a marker interface that does nothing.

It changes the behavior of the protected clone method to give a field-by-field (reference) copy of the object.

Answer

Correct Answer: It changes the behavior of the protected clone method to give a field-by-field (reference) copy of the object.

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28. The TreeMap and LinkedHashMap classes:

Enable iteration of a map's entries based on natural ordering of keys only.

Enable iteration of a map's entries based on the insertion order of elements only.

Enable iteration of a map's entries based either natural ordering of keys OR natural ordering of values - depending on the arguments sent to the constructor.

Enable iteration of a map's entries in a deterministic order.

Answer

Correct Answer: Enable iteration of a map's entries in a deterministic order.

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29. You want to listen TCP connections on port 9000. How would you create the socket?

new Socket(9000);

new ServerSocket(9000);

new Socket(“localhost”, 9000);

new ServerSocket(“localhost”, 9000);

Answer

Correct Answer: new ServerSocket(9000);

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30. public class Test{ public static void main(String [] arg){ int x=10; if(x++ > 10 && x++ == 12){ ++x; } System.out.println(x); } } What is the Output of this code?

Answer

Correct Answer: 11

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31. What is the output of the below code ? int a = 0; int b = 0; if (a++ == 1 && b++ == 1); System.out.println(a + " " + b);

0 0

1 1

1 0

0 1

Answer

Correct Answer: 1 0

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32. What is the output? public static void main(String[] args) { int x=10; if(x++ > 9 && x++ == 12){ ++x; } System.out.println(x); }

Answer

Correct Answer: 12

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33. You need to keep a list of one million objects sorted at all times having 100 random inserts and delete per second. Reads from the list are always done in sorted order. You would:

Use a shell sort after each insert.

Use a PriorityQueue to keep the list ordered at all times.

Use a TreeMap for fast inserts and iterate over the list in order to re-sort it after each insert.

Use a HashMap to keep the list ordered at all times.

Answer

Correct Answer: Use a PriorityQueue to keep the list ordered at all times.

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34. Which of the following are not a valid declarations?

float f = (float)1.2;

float f = 1.2;

float f =1;

float f = 1.2f;

Answer

Correct Answer: float f = 1.2;

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35. True or false: Lambdas allow you to change single instance's method logic

FALSE

TRUE

Answer

Correct Answer: FALSE

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36. Which code fragments correctly create and initialize a static array of int elements?

static final int[] a; static void init() { a = new int[3]; a[0]=100; a[1]=200; }

static final int[] a; static { a=new int[2]; a[0]=100; a[1]=200; }

static final int[] a = new int[2]{ 100,200 };

static final int a = { 100,200 };

Answer

Correct Answer: static final int[] a; static { a=new int[2]; a[0]=100; a[1]=200; }

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37. What is the output of the following program? import java.lang.reflect.Method; class TestImpl { public void method() {} public static void main(String[] args) { Method method = TestImpl.class.getMethod("method", null); System.out.println(method.getName()); } }

Compilation Error

public void test.TestImpl.method()

None of the Above

Answer

Correct Answer: Compilation Error

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38. I would implement a LRU cache using only JDK classes by...

An ArrayList and binary search over the last accessed timestamp

A Hashtable and iteration over all values that contain a last accessed timestamp.

A TreeMap and iteration over values that containing a last accessed timestamp

A LinkedList and binary search over the last accessed timestamp

Answer

Correct Answer: A TreeMap and iteration over values that containing a last accessed timestamp

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39. Which two are valid constructors for Thread? 1. Thread(Runnable r, String name) 2. Thread() 3. Thread(int priority) 4. Thread(Runnable r, ThreadGroup g) 5. Thread(Runnable r, int priority)

1 and 3

1 and 4

1 and 2

2 and 5

2 and 4

Answer

Correct Answer: 1 and 2

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40. The TreeMap class is Java's implementation of which data structure?

B-tree

Red-Black tree

B+ tree

Linked list

Answer

Correct Answer: Red-Black tree

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41. A "blank" final variable (defined without an initial value):

Can be initialized later, but only in a single location

Will raise an exception if its value is accessed or assigned at runtime

Has a Null value, and will raise an exception if initialized or assigned later

Is illegal, and will cause an error at compile time

Answer

Correct Answer: Can be initialized later, but only in a single location

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42. The keyword that ensures a field is coherently accessed by multiple threads is:

"synchronized"

"native"

"switch"

"volatile"

Answer

Correct Answer: "volatile"

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43. which statement is True ?

The notify() method causes a thread to immediately release its locks.

The notify() method is defined in class java.lang.Thread.

To call wait(), an object must own the lock on the thread.

The notifyAll() method must be called from a synchronized context.

Answer

Correct Answer: The notifyAll() method must be called from a synchronized context.

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44. Given the code: Integer i= new Integer("1"); if (i.toString() == i.toString()) System.out.println("Equal"); else System.out.println("Not Equal");

Compiler error

Prints "Equal"

Prints "Not Equal"

None of the above

Answer

Correct Answer: Prints "Not Equal"

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45. Which one of the following statements is true about threads in Java

the notify() must be called to wake up threads that have called wait() and notifyAll() must be called to wake up threads that have called join().

the notify() method can not be called if your class extends Thread class, it can only be called if your class implements the “Runnable” interface

the notify() method can only be called from inside a synchronized block or from a synchronized method

the notify() method informs the Java Virtual Machine that it has finished executing

Answer

Correct Answer: the notify() method can only be called from inside a synchronized block or from a synchronized method

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46. Which four options describe the correct default values for array elements of the types indicated? 1. int -> 0 2. String -> "null" 3. Dog -> null 4. char -> '\u0000' 5. float -> 0.0f 6. boolean -> true

1, 2, 3, 4

1, 3, 4, 5

2, 4, 5, 6

3, 4, 5, 6

Answer

Correct Answer: 1, 3, 4, 5

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47. LinkedBlockingQueue is useful for...

implementing a stack

implementing a producer consumer pattern

binary searches of a list of sorted objects

a synchronized linked list

Answer

Correct Answer: implementing a producer consumer pattern

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48. Does Java 8 allow static methods in interfaces?

Yes, but only private static methods are allowed

Yes

Answer

Correct Answer: Yes

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49. java.util.Collection is:

An interface of non-destructive methods used by Set and List classes

An abstract interface representing a group of objects, extended by Set and List

An interface for iterable groups of objects

An abstract class representing a group of objects, extended by Set and List

Answer

Correct Answer: An interface for iterable groups of objects

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50. What's the output of following error ? class A { public Number getNumber(){ return 1; } } class B extends A { public int getNumber(){ return 2; } } public class Main{ public static void main(String []args){ A a = new B(); System.out.println(a.getNumber()); } }

RuntimeError

Compilation error

Answer

Correct Answer: Compilation error

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51. Anonymous inner classes have access to...

Any local variables in the containing scope

Final, local variables in the containing scope

Only synchronized collections in the containing class

Only variables passed into the constructor, and no variables in the containing class

Answer

Correct Answer: Final, local variables in the containing scope

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52. All of the classes in the Java Collections Framework:

Have methods to retrieve their data as an Array

Have methods allowing them to be viewed as both Maps and Lists

Involve data structures backed by Arrays

Allow elements to be added to the beginning or end of their internal List

Answer

Correct Answer: Have methods to retrieve their data as an Array

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53. Float p = new Float(3.14f); if (p > 3) { System.out.print("p is bigger than 3. "); } else { System.out.print("p is not bigger than 3. "); } finally { System.out.println("Have a nice day."); } What is the result?

p is bigger than 3. Have a nice day.

p is not bigger than 3. Have a nice day.

Compilation fails.

p is bigger than 3.

Answer

Correct Answer: Compilation fails.

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54. In your program, you need to read a zip file (myfile.zip) containing several other data files containing basic Java objects. Which of the following will allow you to construct a InputStream for the task?

new ObjectInputStream(new ZipInputStream( new FileInputStream((“myfile.zip”)));

new ZipInputStream(new ObjectInputStream(“myfile.zip”));

new ZipInputStream(new FileInputStream(“myfile.zip”));

new DataInputStream(new FileInputStream(“myfile.zip”));

Answer

Correct Answer: new ObjectInputStream(new ZipInputStream( new FileInputStream((“myfile.zip”)));

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55. Which statement is true?

Any statement that can throw an Exception must be enclosed in a try block.

Any statement that can throw an Error must be enclosed in a try block.

The Error class is a RuntimeException.

catch(X x) can catch subclasses of X where X is a subclass of Exception.

Answer

Correct Answer: catch(X x) can catch subclasses of X where X is a subclass of Exception.

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56. To create a single instance of a class, we can go with

Static class

(none of these)

Abstract class

Final class

Answer

Correct Answer: (none of these)

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57. Is "Method" a part of Java Reflection API

It is part of Java language, but not part of Reflection API

Yes

Answer

Correct Answer: Yes

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58. What type should you use for floating point monetary calculations?

byte

BigDecimal

double

float

Answer

Correct Answer: BigDecimal

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59. Does interrupt() always force all threads to terminate?

Yes, after interrupt() is called a thread terminates immediatelly

No, if the interruption is not enabled for the thread, it will not terminate

Yes, the thread gets to a predefined interruption point and stops

Answer

Correct Answer: No, if the interruption is not enabled for the thread, it will not terminate

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60. class X implements Runnable { public static void main(String args[]) { /* Missing code? */ } public void run() {} } Which of the following line of code is suitable to start a thread ?

X run = new X(); Thread t = new Thread(run); t.start();

Thread t = new Thread(); x.run();

Thread t = new Thread(X);

Thread t = new Thread(X); t.start();

Answer

Correct Answer: X run = new X(); Thread t = new Thread(run); t.start();

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61. Which of the following statements about static inner classes is true?

A static inner class requires an instance of the enclosing class.

A static inner class requires a static initializer.

A static inner class has no reference to an instance of the enclosing class.

A static inner class has access to the non-static members of the outer class.

Answer

Correct Answer: A static inner class has no reference to an instance of the enclosing class.

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62. What will be printed out if you attempt to compile and run the following code? int i=9; switch (i) { default: System.out.println("default "); case 0: System.out.println("zero "); break; case 1: System.out.println("one "); case 2: System.out.println("two "); }

no output displayed

error default clause not defined

default

default zero

Answer

Correct Answer: default zero

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63. Can the "main" method be overloaded

Yes

Answer

Correct Answer: Yes

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64. Java variables are passed into methods as:

Pass-by Reference

Neither

Pass-by Value

Answer

Correct Answer: Pass-by Reference

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65. What is the issue with the following code? String s = ""; for(int i = 0; i < 1000000; i++) { s += Integer.toString(i); }

There are no issues with the above code.

It will perform very slowly because strings are immutable.

It will not compile.

It will perform very slowly because Integer.toString() is slow.

Answer

Correct Answer: It will perform very slowly because strings are immutable.

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66. Java source code is compiled into

Byte Code

.class

Source Code

.obj

.Exe

Answer

Correct Answer: Byte Code

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67. What is the direct parent of "Error" class?

Exception

Throwable

RuntimeException

Answer

Correct Answer: Throwable

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68. A class implementing a singleton pattern has...

no public constructors, a public static factory method, a static instance variable.

public constructors instead of a static factory method and a static instance variable.

no public constructors, a private static factory method, a static instance variable.

no public constructors and static factory method and a non-static instance variables.

Answer

Correct Answer: no public constructors, a public static factory method, a static instance variable.

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69. Which is a valid keyword in java?

interface

unsigned

int

string

Float

Answer

Correct Answer: interface

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70. What is a weak reference?

A reference to an object which has been garbage collected.

A reference to an object which may have been garbage collected when the object is asked for.

A reference to an object that cannot be garbage collected.

A reference to an object which is about to be garbage collected.

Answer

Correct Answer: A reference to an object which may have been garbage collected when the object is asked for.

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71. How do you convert int[] to a ArrayList<Integer>?

Using toArrayList()

In a loop, creating new Integers.

Using the static Arrays.asList method

Casting

Answer

Correct Answer: Using the static Arrays.asList method

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72. ’blank" final variable (defined without an initial value:

Will raise an exception if its value is accessed or assigned at runtime

Has a Null value, and will raise an exception if initialized or assigned later

Is illegal, and will cause an error at compile time

Can be initialized later, but only in a single location

Answer

Correct Answer: Can be initialized later, but only in a single location

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73. enum Example { ONE, TWO, THREE } Which statement is true?

The expressions (ONE == ONE) and ONE.equals(ONE) are both guaranteed to be true.

The Example values cannot be used in a raw java.util.HashMap; instead, the programmer must use a java.util.EnumMap.

The Example values can be used in a java.util.SortedSet, but the set will NOT be sorted because enumerated types do NOT implement java.lang.Comparable.

The expression (ONE < TWO) is guaranteed to be true and ONE.compareTo(TWO) is guaranteed to be less than one.

Answer

Correct Answer: The expressions (ONE == ONE) and ONE.equals(ONE) are both guaranteed to be true.

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74. Which of the following is true about overloading vs overriding methods?

Overloading can arbitrarily change the access of a method, while overriding can only make it more restrictive

Final methods can be overriden, but not overloaded

Overloading happens at compile time, while overriding happens at runtime

The argument list of overloaded methods must be of same data type (unlike overridden methods)

Answer

Correct Answer: Overloading happens at compile time, while overriding happens at runtime

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75. Output of Program: class Test {public static void main(String[] ar) {int i=0; if(i) System.out.print("hi"); else System.out.print("bye"); } }

Runtime error: incompatible types

bye

Compilation error: incompatible types

Answer

Correct Answer: Compilation error: incompatible types

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76. Java's String class is

Immutable, but can be subclassed

Final, with immutable instances

Mutable, and can be subclassed

Final, but creates mutable instances

Answer

Correct Answer: Final, with immutable instances

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77. public class SomeClass { public static void main(String[] args) { System.out.println((String) null); } } What is the result of the following program?

The code throws NullPointerException.

The code does not compile.

The code prints "null" on console.

Answer

Correct Answer: The code prints "null" on console.

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78. Java's automatic memory management:

Can be overriden using functions like alloc and dalloc

Can be tuned using Virtual Machine settings

Can be configured to operate statically or dynamically at compile time

Uses hardcoded settings inside each Virtual Machine, which should not be altered

Answer

Correct Answer: Can be tuned using Virtual Machine settings

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79. After the following code fragment, what is the value in a? String s; int a; s = "Foolish boy."; a = s.indexOf("fool");

-1

random value

Answer

Correct Answer: -1

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80. Which option is true for StringBuffer and StringBuilder

StringBuffer are not thread safe and StringBuilder are thread safe.

Neither StringBuffer nor StringBuilder are thread safe.

StringBuffer and StringBuilder are thread safe.

StringBuffer are thread safe and StringBuilder are not thread safe

Answer

Correct Answer: StringBuffer are thread safe and StringBuilder are not thread safe

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81. Which of the following is used to see the details of compilation

javac -detail TestExample.java

javac -verbose TestExample.java

javac -debug TestExample.java

None of these

Answer

Correct Answer: javac -verbose TestExample.java

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82. enum Example { ONE, TWO, THREE } Which statement is true?

The expressions (ONE == ONE) and ONE.equals(ONE) are both guaranteed to be true.

The Example values cannot be used in a raw java.util.HashMap; instead, the programmer must use a java.util.EnumMap.

The Example values can be used in a java.util.SortedSet, but the set will NOT be sorted because enumerated types do NOT implement java.lang.Comparable.

The expression (ONE < TWO) is guaranteed to be true and ONE.compareTo(TWO) is guaranteed to be less than one.

Answer

Correct Answer: The expressions (ONE == ONE) and ONE.equals(ONE) are both guaranteed to be true.

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83. The List interface has which superinterfaces?

Set

Both Collection and Iterable

Collection

Iterable

Answer

Correct Answer: Both Collection and Iterable

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84. Which is a reserved word in the Java programming language?

reference

array

native

subclasses

method

Answer

Correct Answer: native

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85. A method without an access modifier (i.e. public, private, protected) is...

private

package-private

protected

static

public

Answer

Correct Answer: package-private

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86. In addition to CORBA, Core Java also supports network services using:

IPX / SPX Protocol

Remote Method Invocation

Remote Procedure Calls

Remote Object Access

Answer

Correct Answer: Remote Method Invocation

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87. Which one of these lists contains only Java programming language keywords?

strictfp, constant, super, implements, do

try, virtual, throw, final, volatile, transient

class, if, void, long, int, continue

byte, break, assert, switch, include

goto, instanceof, native, finally, default, throws

Answer

Correct Answer: class, if, void, long, int, continue

Note: This Question is unanswered, help us to find answer for this one

88. Which class/classes is/are thread safe among these?

String and StringBuffer

StringBuilder

Answer

Correct Answer: String and StringBuffer

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89. What is the difference between a checked and unchecked exception?

A checked exception extends Throwable and an unchecked exception does not.

An unchecked exception extends Throwable and a checked exception does not.

Unchecked exceptions must be caught while checked do not need to be caught

Checked exceptions must be caught while unchecked do not need to be caught

Answer

Correct Answer: Checked exceptions must be caught while unchecked do not need to be caught

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90. Java provides a class for mutable sequences of characters, called:

MutableString

String

StringBuffer

CharSequence

Answer

Correct Answer: StringBuffer

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91. What is the correct statement for handling RuntimeException?

It has to be surrounded by try-catch on place

It has to be marked using "throws" keyword on method declaration

It should not be caught, as this exception represents programmer error that should be fixed.

It can be handled by try-catch on place, but it can also be propagated using "throws" keyword

Answer

Correct Answer: It can be handled by try-catch on place, but it can also be propagated using "throws" keyword

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92. Immutable objects are always...

memory efficient

thread safe

polymorphic

serializable

Answer

Correct Answer: thread safe

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93. A class may extend:

Only one interface

Only one non-final class

Many classes through multiple inheritance

Only one inner class

Answer

Correct Answer: Only one non-final class

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94. What is the output? int[] xxx = {10, 20}; List<String> list = new ArrayList<String>(10); list.add("01"); list.add("02"); System.out.println(xxx.length + ", " +list.size());

2, 10

1, 2

10, 2

Compile error

2, 2

Answer

Correct Answer: 2, 2

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95. Calling System.gc() when using a modern JVM :

Is especially important when programming for mobile or memory limited devices.

Does not necessarily force garbage collection to occur, and is not idiomatic java.

Should be done after deleting several elements from a collection.

Is the most straightforward and reliable way to perform memory management in Java.

Directly and immediately disposes of all orphaned objects on the heap.

Answer

Correct Answer: Does not necessarily force garbage collection to occur, and is not idiomatic java.

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96. Which one of the following statements is true about Java Beans?

Java Beans are user defined classes.

All Java Beans must extend the java.bean base class

Java Beans cannot be used in server side programming, they are only used for Graphical User Interfaces.

Java Beans are not permitted to create any threads

Answer

Correct Answer: Java Beans are user defined classes.

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97. Which is the correct command to run an executable JAR file named program.jar?

jar program.jar

java -jar program.jar

jar -run program

java -jar program

java -run program.jar

Answer

Correct Answer: java -jar program.jar

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98. What is the name of the method used to start a thread execution?

init();

start();

resume();

run();

Answer

Correct Answer: start();

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99. Why is it important to override hashCode() when you override equals()?

equals() will throw an exception if hashCode() is not overridden as well.

It is NOT important to override hashCode() when overriding equals().

Overriding equals without hashCode breaks the contract of hashCode().

Answer

Correct Answer: Overriding equals without hashCode breaks the contract of hashCode().

Note: This Question is unanswered, help us to find answer for this one

100. An "overloaded" method has what in common with one (or more) methods on the same class?

The same name

The same number and types of parameters

The same number of parameters, regardless of type

The same return type

Answer

Correct Answer: The same name

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101. When the == comparator is used on two objects, it checks to see if they:

Are instances of the same class

Evaluate to the same value

Have the same value according to the .equals() method of the first object

Are references to exactly the same object

Answer

Correct Answer: Are references to exactly the same object

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102. You want subclasses in any package to have access to members of a superclass. Which is the most restrictive access that accomplishes this objective?

transient

private

protected

public

Answer

Correct Answer: protected

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103. The instanceof operator can be used to determine if an object is:

An instance of a class that implements a given interface

(All of these)

An instance of a class

An instance of a subclass of a class

Answer

Correct Answer: (All of these)

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104. When creating a user defined class for storing objects in a HashMap, which method(s) should be overridden?

The equal() method

The hashCode() method

The constructor method

Both the equals() and hashCode() methods

(You don't need override any methods)

Answer

Correct Answer: Both the equals() and hashCode() methods

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105. On which Java major release were Lambdas introduced?

Java 6

Java 5

Java 7

Java 8

Answer

Correct Answer: Java 8

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106. What are all the different types of access modifiers in Java

private, public

private, protected, default, public

private, protected, public

protected, default, public

private, default, public

Answer

Correct Answer: private, protected, default, public

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107. The "static" keyword marks something as:

Not being mutable after initialization

A constant variable whose value cannot be changed

No longer able to be subclassed or overloaded

Belonging to a class, rather than a specific instance

Answer

Correct Answer: Belonging to a class, rather than a specific instance

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108. Is it a good pratcice to catch "Throwable"?

yes

Answer

Correct Answer: yes

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109. JDBC addresses the issue of transactions.

True

False

Answer

Correct Answer: True

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110. The "java" command line tool is used to:

Compress collections of java class files into .jar archives

Load and execute java .class files

Disassemble .class files back into readable source code

Compile java source files into bytecode class files

Answer

Correct Answer: Load and execute java .class files

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111. What is the benefit of ConcurrentHashMap<K,V>?

Allows null to be used a key or value

It maintains a list through all entries to retrieve data in the order it was inserted.

All operations are thread-safe and retrieval operations do not entail locking

Supports locking the entire table in a way that prevents all access

Answer

Correct Answer: All operations are thread-safe and retrieval operations do not entail locking

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112. How should you create a new class that maps keys to values, using the Java Collections Framework?

Implement the Queue, List, and Array interfaces

Implement the Map interface, possibly by extending the AbstractMap class

Implement both the Iterator and Array interfaces

Extend the AbstractCollection class, thereby implementing the AbstractCollection interface

Answer

Correct Answer: Implement the Map interface, possibly by extending the AbstractMap class

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113. What is the output of the below code ? int a = 0; int b = 0; if (a++ == 1 || b++ == 1) {} System.out.println(a + " " + b);

0 1

0 0

1 0

1 1

Answer

Correct Answer: 1 1

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114. What will below method return? public foo(){ int x = 5; return x; }

Runtime error

null

Compile error

Answer

Correct Answer: Compile error

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115. How can we use the class or jar files kept on the network path, within our projects?

mentioning the Class /Jar file names during compilation only

by directly copying and including in the same folder as of the project

No the network files can not be used directly

Including the path and class /jar file name in the Classpath

mentioning the file names in the Path

Answer

Correct Answer: Including the path and class /jar file name in the Classpath

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116. What will be the output of the program? public class Foo { public static void main(String[] args) { try { return; } finally { System.out.println( "Finally" ); } } }

Finally

Compilation fails.

The code runs with no output.

An exception is thrown at runtime.

Answer

Correct Answer: Finally

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117. package test; class Test { } ---------------- package test; class SubTest extends Test{ } Does this code compile without errors if the classes are in separate files?

Yes

Answer

Correct Answer: Yes

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118. Reflection mechanism allows to:

Delegate configuration to XML file

Modify and inspect properties and methods of objects, even if they are protected or private

Answer

Correct Answer: Modify and inspect properties and methods of objects, even if they are protected or private

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119. What is auto boxing?

JVM conversion of int to float values

Automatic insertion of brackets by an IDE

It doesn’t occur in Java, only in dynamically typed JVM languages like Groovy

JVM conversion between primitive types and reference types

Answer

Correct Answer: JVM conversion between primitive types and reference types

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120. Keyword used to access members or methods of superclass?

this

Super

extends

native

Answer

Correct Answer: Super

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121. Can an abstract class be a final class?

Yes

Answer

Correct Answer: No

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122. Which of these is true?

An interface implements another interface and class

A class implements and extends a class

An interrface extends a class but implements another interface

A class implements an interface but extends a class

Answer

Correct Answer: A class implements an interface but extends a class

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123. What method should you always override when you have overridden the equals() method?

hashCode()

toString()

wait()

clone()

Answer

Correct Answer: hashCode()

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124. When you create a thread with the “new” operator – which one of the following statements is true about its state

it will be “runnable” when start() method is called

it is in “runnable” state

it is blocked until another thread calls notify()

it starts running immediately

Answer

Correct Answer: it will be “runnable” when start() method is called

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125. public class SomeClass { public static void main(String[] args) { System.out.println((String) null); } } Does this code compile without errors?

Yes

Answer

Correct Answer: Yes

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126. How can you stop your class from being inherited by another class?

Declare the class default constructor as private.

Declare the class as final.

Declare the class as abstract.

It’s not possible.

Answer

Correct Answer: Declare the class as final.

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127. The Thread.sleep() method:

Suspends execution in synchronized methods only

Causes the hosted virtual machine to suspend all forms of execution

Causes all threads to suspend execution

Causes the current thread to suspend execution

Answer

Correct Answer: Causes the current thread to suspend execution

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128. Which of the following is a valid constructor signature?

public void className()

public static className()

static className()

public className()

Answer

Correct Answer: public className()

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129. What is the most efficient way to concatenate a large number of strings in Java?

The StringBuffer object.

The + operator.

Answer

Correct Answer: The StringBuffer object.

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130. Which of these are advantages of encapsulation in Java?

Encapsulation reduces coupling of modules and increase cohesion inside a module

Encapsulation in Java makes unit testing easy

All of these

Encapsulated code is easy to change with new requirements

Answer

Correct Answer: All of these

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131. To document an API, which tool do you use?

javaApi

documentcreate

javadoc

apicreate

Answer

Correct Answer: javadoc

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132. If we want a class not to be overridden,the class must be done as

Class should be abstract

Class should public

Class should be final

Class should be static

Answer

Correct Answer: Class should be final

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133. What is the correct syntax for importing java.util.Scanner?

import. java.util.Scanner;

import.java.util.scanner;

import.java.util.scanner.

import java.util.Scanner;

Answer

Correct Answer: import java.util.Scanner;

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134. To define a child class from the Parent class following is used:

class Child extends Parent

class Child : Parent

class Child extends Public Parent

class Child :: Parent

Answer

Correct Answer: class Child extends Parent

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135. The part of a "try" block that is always executed is:

"if"

"import"

"enum"

"finally"

Answer

Correct Answer: "finally"

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136. The most reliable way to compare two Strings for equality is by:

Using the .equals() or .compareTo() method of one object on the other

Using the == operator on the .value() of each object

Using the &= operator on the objects

Using the == operator on the objects

Answer

Correct Answer: Using the .equals() or .compareTo() method of one object on the other

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137. Which additional keyword may be used with try-catch blocks?

finish

finalize

finally

final

Answer

Correct Answer: finally

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138. Java handles memory allocation and reuse using a process called:

Buddy Blocks

Garbage Collection

Virtual Memory

Manual Memory Management

Answer

Correct Answer: Garbage Collection

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139. The "javac" command line tool is used to:

Convert java bytecode files into native executables

Compress collections of java class files into .jar archives

Compile java source files into bytecode class files

Generate C headers and stubs for native methods

Answer

Correct Answer: Compile java source files into bytecode class files

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140. What is an example of proper capitalization for a class name?

camELCase

CAMELcase

CamelCase

camelcase

Answer

Correct Answer: CamelCase

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141. If a method or variable is marked as having the "private" access level, then it can only be accessed from:

Inside the same class

Inside the same class, or any of its superclasses

Inside the same class, or a subclass

Inside the same class or its parent class

Answer

Correct Answer: Inside the same class

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142. Finally is used to....

ensure a block of code is executed when the JVM shuts down.

ensure a block of code is executed only when try/catch completes without an exception

ensure a block of code is executed only when try/catch completes with an exception

ensure a block of code is always executed after a try/catch

Answer

Correct Answer: ensure a block of code is always executed after a try/catch

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143. A java class which extends another class is usually described with the word:

subclass

dynamic

abstract

overloaded

Answer

Correct Answer: subclass

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144. Which will legally declare, construct, and initialize an array?

int myList [] [] = {4,9,7,0};

int [] myList = {"1", "2", "3"};

int [] myList = (5, 8, 2);

int myList [] = {4, 3, 7};

Answer

Correct Answer: int myList [] = {4, 3, 7};

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145. The Object.wait() method:

Resumes from waiting if notifyAll() is invoked for the object

Resumes from waiting if notify() is invoked for the object

Causes the current thread to wait

Resumes from waiting if a specified amount of time has elapsed

Answer

Correct Answer: Causes the current thread to wait

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146. Interfaces are useful for...

making an abstract class concrete

reducing heap size

creating a design contract that encapsulates implementation

implementing an abstract factory pattern

Answer

Correct Answer: creating a design contract that encapsulates implementation

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147. Given following code, what will be the output: import java.lang.reflect.Method; class Bar { private int bar(int a) { return a * a; } } public class Foo { public static void main(String[] args) { try { Bar bar = new Bar(); Method method = bar.getClass().getDeclaredMethod("bar", int.class); method.setAccessible(true); System.out.println(method.invoke(bar, new Integer(5))); } catch (Exception e) { e.printStackTrace(); System.out.println("Error"); } } }

Null

IllegalAccessException will be thrown

CompileError

Answer

Correct Answer: 25

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148. True of False? The strictfp keyword ensures that you get the same result on every platform if you perform operations in the floating point variable.

True

False

Answer

Correct Answer: True

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149. What is the correct way to create an instance of a class?

ClassName varName = new ClassName(new ClassName);

ClassName varName = new ClassName(arguments);

varName ClassName = new varName(arguments);

ClassName varName => new ClassName();

Answer

Correct Answer: ClassName varName = new ClassName(arguments);

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150. The Core Java platform provides many benefits to developers, including:

A consistent programming interface across multiple hardware platforms

Superior speed and performance compared to native code

A purely functional programming language with a minimalist design philosophy

Direct compilation to native code on most platforms

Answer

Correct Answer: A consistent programming interface across multiple hardware platforms

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151. What will be the output of program? class Ab { public static void main(String[] ar) {System.out.print("hi"); } static { System.out.print("how"); } }

runtime error

hihow

howhi

compilation error: At Static

Answer

Correct Answer: howhi

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152. Which one of the following is NOT a reserved word in Java?

public

private

virtual

final

Answer

Correct Answer: virtual

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