Java Interview Questions

1. public class Sample {

public static void main (String [] args) {

System.out.println ((1==1)? (7==8)? 5:6:4);

}

ANSWER: 6

EXPLANATION: (1==1) returns true. So (7==8) gets evaluated which in turn returns false. So 6 will get displayed.

2. public class Sample{

public static void main (String [] args) {

System.out.println (Math.round (Math.random ()));

}

ANSWER: prints either 0 or 1 only

EXPLANATION: Math.random returns a double value that is greater than or equal to 0.0 but less than 1.0

3. public class Sample{

public static void task (int no) {

System.out.print (no%10);

if ((no/10) != 0)

task (no/10);

System.out.print (no%10);

}

public static void main (String [] args) {

Sample.task (1248);

}

ANSWER: 84211248

EXPLANATION: Recursion is implemented using stacks. After recursive calls get finished, the second print statement will be executed. Since stack models LIFO, what is printed first by the recursive call will get processed last.

4. public class Sample{

public static void main (String [] args) {

int a=1, b=13;

if ((b< (a=a+a)) || (b< (a=a+a)) || (b< (a=a+a)) || (b< (a=a+a)) || (b< (a=a+a)))

System.out.println (b-a);

else

System.out.println (b+a);

}

ANSWER: -3

EXPLANATION: The || operator does not evaluate its right operand, if its left operand evaluated to be true. When the 4^th condition gets evaluated, the value of “a” becomes 8. So the condition returns true (13<8+8). Therefore (b-a) is nothing but 13-16=-3.

HINT: Try the conditional statement after replacing || with && or &.

5. Math.ceil(x) has the same value as –Math.floor(-x).

EXAMPLE: Math.ceil(5.3) is 6.0

-Math.floor(-5.3) is also 6.0

HINT: Also Math.max(m,n) is same as –Math.min(-m,-n) and

Math.floor(m+0.5) is equivalent to Math.round(m)

6. Object is the only class without a superclass. In other words Object is the superclass of all the classes existing in java. If a class does not explicitly extend any other class, it extends the Object class by default.

7. ; is a statement that does nothing.

8. Automatic conversion from primitive type to an Object of the corresponding Wrapper class is called boxing.

EXAMPLE: int to Integer

boolean to Boolean

9. public class Sample{

public static void main (String [] args) {

boolean a=false, b=false;

if (! a&&a)

System.out.println ("if");

else

System.out.println ("else");

}

ANSWER: else

EXPLANATION: The condition (! a&&a) will be interpreted as ((!a) && a). This evaluates to false.

HINT: If the condition is rewritten as (! (a&&a)), it will be evaluated to true.

10. Consider the following 2 statements & predict which one will execute faster.

a. a>b ? a : b

b. Math.max(a,b)

EXPLANATION: a runs faster than b because of the function call overhead associated with b.

11. public class Sample{

public static void main(String[] args){

int s=1;

if(s)

System.out.println(s);

}

ANSWER: results in compilation error.

EXPLANATION: Java cannot convert integer into boolean. In C/C++ 0 is false and any non-zero value is true.

12. public class Sample{

public static void main(String[] args){

boolean [] ages = new boolean[4];

System.out.println(ages[0]==ages[1]);

}

ANSWER: displays true.

EXPLANATION: The elements of boolean array will be initialized to false by default. So false == false becomes true.

13. public class Sample{

public static void main(String[] args){

System.out.println((int)Math.ceil(Math.random()*40+10));

System.out.println((int)Math.round(Math.random()*40+10));

}

ANSWER: Returns a random integer in the range of 10 to 50(both inclusive).

14. What is the impact of declaring a class, method and variable as final?

ANSWER: Classes declared as final cannot be extended.

Methods declared as final cannot be overridden.

Variables declared as final can be assigned only once.

15. Define PATH and CLASSPATH.

ANSWER:
* PATH maintains a list of directories from where the OS searches the PATH entries for executable programs such as javac and java.

* CLASSPATH is the environment variable that contains a list of directories from where java looks for classes referenced in a program.

16. Categorize java Variables:

ANSWER:

Class Variable

Instance Variable

Local Variable

Array Component Variable

Method Parameter Variable

Constructor Parameter Variable

Exception Handler Parameter Variable

17. Mention the order in which user defined classes will be searched:

ANSWER:

By default looks into the current working directory (.).

Entries in the CLASSPATH environment variable, which overrides the default.

Entries in the -cp (or -classpath) command-line option, which overrides the CLASSPATH environment variable.

The runtime command-line option -jar, which overrides all the above.

18. Why String has been made immutable in Java?

ANSWER: String has been made immutable in Java to enhance 'Security’. The filenames in Java are specified by using Strings. With Strings being immutable, JVM can make sure that the filename instance member of the corresponding File object would keep pointing to same unchanged "filename" String object. The 'filename' instance member being a 'final' in the File class can anyway not be modified to point to any other String object specifying any other file than the intended one (the one which was used to create the File object).

19. Brief about Garbage Collection.

ANSWER: Objects are created on heap in Java.

Garbage collection is a mechanism provided by JVM to reclaim heap space from Objects which are eligible for Garbage collection. Object becomes eligible for garbage collection if all of its references are null.

Garbage collection relieves Java programmer from memory management, which is essential part of C++ programming and gives more time to focus on business logic.

Garbage Collection is carried by a daemon thread called Garbage Collector.
Before removing an Object from memory, Garbage collection thread invokes finalize() method of that Object and gives an opportunity to perform any sort of cleanup required.

A Java programmer cannot force Garbage collection; it will only trigger if JVM thinks it needs a garbage collection based on Java heap size.

There are methods like System.gc () and Runtime.gc () which is used to send request of Garbage collection to JVM but it’s not guaranteed that garbage collection will happen.

If there is no memory space for creating new Object in Heap JVM throws OutOfMemoryError.

20. Coercion is another name for an implicit typecast, i.e. one mandated by the language rules, and not explicitly added by the programmer.

21. Differentiate final, finally and finalize.

ANSWER:

final is a keyword/modifier. Refer answer no. 14.

finally is a block. The finally block is executed even if an unexpected exception occurs. But finally is useful for more than just exception handling - it allows the programmer to avoid having cleanup code accidentally bypassed by a return, continue, or break statement. Putting cleanup code in a finally block is always a good practice, even when no exceptions are anticipated.

finalize is a method. Before an object is garbage collected, finalize() method gets invoked. We can write system resources release code in finalize() method before getting garbage collected. finalize() neither takes any parameter nor returns anything.

22. Let n be a variable of datatype byte. The value of n<<m is same as n * 2^m.

EXPLANATION: Once shifting left is multiplying by 2

EXAMPLE: byte representation of 13 is 0000 1101

13<<4 becomes 1101 0000 (208) [13 * 2⁴= 208]

23. Can we declare a static variable inside a method?

Static variables are Class level variables and they can't be declared inside a method. If declared, the class will not compile.

24. Why is an Interface be able to extend more than one Interface but a Class can't extend more than one Class?

Basically Java doesn't allow multiple inheritance, so a Class is restricted to extend only one Class. But an Interface is a pure abstraction model and doesn't have inheritance hierarchy like classes(do remember that the base class of all classes is Object). So an Interface is allowed to extend more than one Interface.

25. If a Class is declared without any access modifiers, where may the Class be accessed?

A Class that is declared without any access modifiers is said to have package access. This means that the Class can only be accessed by other Classes that are defined within the same package.

26. What is the preferred size of a Component?

The preferred size of a Component is the minimum Component size that will allow the Component to display normally.

27. What are the differences between Applets and Applications?

Application:
-Applications are Stand Alone and doesn’t need web-browser.
-Execution starts with main().
-May or may not be a GUI.

Applet:
-Needs no explicit installation on local machine. Can be transferred through Internet on to the local machine and may run as part of web-browser.

-Execution starts with init () method.

-Must run within a GUI. (Using AWT/Swing)

28. Can we write abstract methods in a final class and vice versa?

Abstract methods are not allowed in final class. An abstract class can have final methods in it.

29. Why do we require public static void main (String args[]) method in Java program?

public: The method can be accessed outside the class/package.

static: You need not have an instance of the class to access the method.

void: Your application need not return a value, as the JVM launcher would return the value when it exits.

main(): This is the entry point for the application.

30. What would you use to compare two String variables - the operator == or the method equals()?

I'd use the method equals() to compare the values of the Strings and the operator == to check if two variables point at the same instance of a String object.

31. Why abstract and final classes are mutually exclusive?

A class cannot be both final and abstract for obvious reasons. The abstract modifier says it's not complete and no instance can be created for the class; some subclass should provide a concrete implementation of any such abstract method. The final modifier says that the class is complete and cannot be extended. This puts the mutual exclusion of the two.

32. Why we cannot override static methods?

We can declare static methods with same signature in subclass, but it is not considered overriding as there won’t be any run-time polymorphism. Hence the answer is ‘No’. For class (or static) methods, the method according to the type of reference is called, not according to the object being referred, which means method call is decided at compile time. For instance (or non-static) methods, the method is called according to the type of object being referred, not according to the type of reference, which means method call is decided at run time.

EXAMPLE:

// Superclass

class Base {

// Static method in base class which will be hidden in subclass

public static void display() {

System.out.println("Static or Class method from Base");

}

// Non-static method which will be overridden in derived class

public void print() {

System.out.println("Non-static or Instance method from Base");

}

// Subclass

class Derived extends Base {

// This method hides display() in Base

public static void display() {

System.out.println("Static or Class method from Derived");

}

// This method overrides print() in Base

public void print() {

System.out.println("Non-static or Instance method from Derived");

}

// Driver class

public class Sample {

public static void main(String args[ ]) {

Base obj1 = new Derived();

// As per overriding rules this should call to class Derived's static overridden method. Since static method cannot be overridden, it calls Base's display()

obj1.display();

// Here overriding works and Derived's print() is called

obj1.print();

}

OUTPUT:

Static or Class method from Base

Non-static or Instance method from Derived

33. What must a Class do to implement an Interface?

If a Class wants to implement an interface, it should use implements keyword in its Class declaration and provide the definitions to the methods of that Interface or else it should be declared as an abstract class. An Interface specifies what a Class must do. So it can also be understood as an agreement with the implementing Class.

34. Define Immutable Class. How to make a Java Class immutable?

An Immutable Class is one whose state cannot be changed once created.

Some guidelines to make a class immutable:-

a) Don’t provide “setter” methods

This principle says that for all mutable properties in your class, do not provide setter methods. Setter methods are meant to change the state of an object and this is what we want to prevent here.

b) Make all fields final and private

This is another way to increase immutability. Fields declared private will not be accessible outside the class and making them final will ensure that even accidentally you cannot change them.

c) Don’t allow subclasses to override methods

The simplest way to do this is to declare the class as final. Final classes in java cannot be overridden.

35. What is the disadvantage of using threads?

Threads also have some disadvantages. For example threads are not reusable as they are dependent on a process and cannot be separated from the process. Threads are not isolated as they don't have their own address space. The error caused by the thread can kill the entire process or program, because that error affects the entire memory space of all threads used in that process or program.

36. What is the difference between exception and error in java?

Error: Any deviation from the expected behavior of the system or program, which stops the working of the system is an error. Errors are exceptional scenarios that are out of scope of application and it’s not possible to anticipate and recover from them. For example hardware failure, JVM crash or out of memory error. Some of the common Errors are OutOfMemoryError and StackOverflowError.

Exception: Any error or problem which one can handle and continue to work normally. Bad programming also causes exception. Some of the exceptions are FileNotFoundException and ArrayIndexOutOfBoundException.

37. What is the difference between creating a thread by extending Thread class and by implementing Runnable interface?

The most common difference is

When you extends Thread class, after that you can’t extend any other class which you required. (As you know, Java does not allow inheriting more than one class).

When you implements Runnable, you can save a space for your class to extend any other class in future or now.

However, the significant difference is

When you extends Thread class, each of your threads has a unique object associated with it.

When you implements Runnable, many threads can share the same Runnable instance.

EXAMPLE:

class ImplementsRunnable implements Runnable {

private int counter = 0;

public void run() {

counter++;

System.out.println("ImplementsRunnable : Counter : " + counter);

}

class ExtendsThread extends Thread {

private int counter = 0;

public void run() {

counter++;

System.out.println("ExtendsThread : Counter : " + counter);

}

public class Sample {

public static void main(String args[]) throws Exception {

//Multiple threads share the same object.

ImplementsRunnable ir = new ImplementsRunnable();

Thread t1 = new Thread(ir);

t1.start();

Thread.sleep(1000); // Waiting for 1 second before starting next thread

Thread t2 = new Thread(ir);

t2.start();

Thread.sleep(1000);

Thread t3 = new Thread(ir);

t3.start();

//Creating new instance for every thread access.

ExtendsThread et1 = new ExtendsThread();

et1.start();

Thread.sleep(1000);

ExtendsThread et2 = new ExtendsThread();

et2.start();

Thread.sleep(1000);

ExtendsThread et3 = new ExtendsThread();

et3.start();

}

OUTPUT:

ImplementsRunnable : Counter : 1

ImplementsRunnable : Counter : 2

ImplementsRunnable : Counter : 3

ExtendsThread : Counter : 1

EXPLANATION:

In the Runnable interface approach, only one instance of a class is being created and it has been shared by different threads. So the value of counter is incremented for each and every thread access. Whereas, in the Thread class approach, you must have to create separate instance for every thread access. Hence different memory is allocated for every class instances and each has separate counter, the value remains same, which means no increment will happen because none of the object reference is same.

38. What is an Object and why initialization is important?

An object is a chunk of memory bundled with the code that manipulates memory. In the memory, the object maintains its state (the values of its instance variables), which can change and evolve throughout its lifetime.

Java makes certain that memory (object's instance variables) is initialized, at least to predictable default values, before it is used by any code. Initialization is important because, historically, uninitialized data has been a common source of bugs. Local variables are not given default initial values. They must be initialized explicitly before they are used.

39. How can one prove that the array is not null but empty?

Print array.length. If it prints 0, it is empty, means array has been initialized with no elements. But if it would have been null then it would have thrown a NullPointerException on attempting to print array.length.

EXPLANATION:

public class Sample{

public static void main(String args[]){

int a[]={};

System.out.println(a.length);

}

OUTPUT:

0 (So array a is understood to be empty)

40. What is a layout manager?

A layout manager is an object that is used to organize components in a container.

41. *Which of the following statement is correct?

a) A reference is stored on heap.

b) A reference is stored on stack.

c) A reference is stored in a queue.

d) A reference is stored in a binary tree.

Choose the most appropriate answer.

42. *Which of these will create and start this thread?

public class MyRunnable implements Runnable{

public void run(){

//some code here.

}

a) new Runnable(MyRunnable).start();

b) new Thread(MyRunnable).run();

c) new Thread(new MyRunnable()).start();

d) new MyRunnable().start();

Choose the most appropriate answer.

43. *In Java, String is ________

a) Array of characters.

b) An object of String class.

c) A sequence of characters.

d) Both a and c.

Choose the most appropriate answer.

44. *public class Sample{

public static void main(String[] args){

System.out.println("Hello "+args[0]);

}

What will be the output of the program, if this code is executed as follows in the command line?

>java Sample world

a) Hello

b) Hello Sample

c) Hello world

d) the code does not run

Choose the most appropriate answer.

45. What is the seed value being used in the no argument constructor of a Random object? Is it possible to generate identical sequence of random values using Random class?

Random() - constructs a Random object with the current time from System clock as its seed. Different Random objects that are created in close succession by a call to the default constructor will have identical default seed values and, therefore, will produce identical sets of random numbers. Also by constructing Random objects with a specified seed will generate identical sequence of random values.

EXAMPLE:

import java.util.*;

public class Sample{

public static void main(String[] args){

Random r1 = new Random(8);

Random r2 = new Random(8);

System.out.print("from random1: ");

for(int i=0;i<5;i++)

System.out.print(r1.nextInt(100)+" "); //returns a random int value bet 0 and 100

System.out.print("\n from random2: ");

for(int i=0;i<5;i++)

System.out.print(r2.nextInt(100)+" ");

}

OUTPUT:

From random1: 64 56 30 21 72

APPLICATION: In software testing we can test our program using a fixed sequence of numbers.

46. How Java achieves platform independency?

The JVM takes on the responsibility of interacting with the hardware rather than forcing the Java programmer to write code specific to each hardware platform. Source code is converted into an intermediate format known as byte code by JAVAC (These are not machine instructions but just an intermediate format - format between Java source code and machine instruction). Java byte codes obtained from javac can be executed on any platform and OS, provided JVM is installed in it. So, we can say that JVM is platform dependent but Java is platform independent.

47. accessor (getter) method Vs mutator(setter) method.

Getters or accessors, are methods that provide access to an object's instance variables. Prefixing the corresponding instance variable with "get" is a common naming convention for getters.

public String getAuthor(){

return author;

}

Setters or mutators, are methods that provide the caller with an opportunity to update the value of a particular instance variable. Similar to getters, setters are often named by prefixing the corresponding instance variable with "set".

public void setAuthor(String author){

this.author = author;

}

Note that, unlike getters, setters have no return value. A setter's job is usually limited to changing the value of an instance variable.

48. Predict the output of the following code and justify your answer.

public class Sample{

void show(Object o){

System.out.println("Object");

}

void show(String s){

System.out.println("String");

}

public static void main(String[] args){

new Sample().show(null);

}

OUTPUT: String

EXPLANATION: That is because String class extends from Object and hence is more specific than Object. Compiler always chooses the most specific method to invoke. The Java programming language uses the rule that the most specific method is chosen.

HINT: If you try to add a method that take an Integer input it will throw error as ambiguous methods, because String and Integer both of them are more specific than Object but none is more specific than the other one.

49. Examine the code given below and find the error.

class Super{

public int getLength(){

return 4;

}

public class Sample extends Super{

public long getLength(){

return 8;

}

public static void main(String[] args){

Super s = new Super();

Sample ss = new Sample();

System.out.println(s.getLength()+","+ss.getLength());

}

ERROR: getLength() in Sample cannot override getLength() in Super; attempting to use incompatible return type.

50. public class Sample{

public static void main(String args[]){

System.out.println("no. of args : "+args.length);

}

What will be the output, when the above code is executed in command line as

a) >java Sample “1 2 3” 4 OUTPUT: 2

b) >java Sample “*” OUTPUT: 1

c) >java Sample OUTPUT: 0

d) >java Sample * OUTPUT: returns the number of directories & files in pwd

51. Does the following code resize the array?

public class Sample{

public static void main(String[] args){

int[] mylist;

mylist = new int[10];

//int[] mylist = {9,8,7,6,5,4,3,2,1,0};

//System.out.println(mylist.length);

//for(int i=0;i<mylist.length;i++)

// System.out.print(mylist[i]+" ");

// sometime later assign a new array to mylist

mylist = new int[20];

//System.out.println("\n"+mylist.length);

//for(int i=0;i<mylist.length;i++)

// System.out.print(mylist[i]+" ");

}

ANSWER: In this example, initially the array has size 10. Once you've decided that the array has 10 elements, you can't make it any bigger or smaller. If you want to change the size, you need to create a new array of the desired size, and then copy elements from the old array to the new array, and use the new array. Here, we are making the reference of old array pointed to the newly created array. If we try to display the elements of the new array, old array elements won’t be there.

52. *Consider the entities – Quadrilateral, Parallelogram and Rectangle. To model these entities in an object-oriented way, they should be modeled as individual classes such that ___________________________________________.

53. *An interactive program asks the question----“Are you right-handed, left-handed or ambidextrous? Type R if right-handed, L if left-handed, A if ambidextrous.” The part of the program(written by student A) that does the appropriate action depending on the user’s response is given below.

if (response == ‘A’) //c1

doThisForAmbidextrous();

else if (response == ‘R’) //c2

doThisForRightHanded();

else if (response == ‘L’) // c3

doThisForLeftHanded();

Student B did the same thing but checked the conditions in the order - c3, c2 and c1.

Student C did the same thing but checked the conditions in the order – c2, c3 and c1.

Student D did the same thing but checked the conditions in the order – c2, c1 and c3.

One of these 4 students got special recognition from the Professor for the order in which the student checked the conditions. Who is the student?

54. How objects will be created in Java?

By using new keyword. This is the most common way to create an object in java. Almost 99% of objects are created in this way.

55. What makes the difference between creating String objects in the following two ways?

a) String s = “Welcome”;

b) String s = new String(“Welcome”);

ANSWER:

a) Creates String literal. String literals work with a concept of String pool. When you create a second String literal with same content, instead of allocating a new space, Compiler will return the same reference. Hence you will get true when you compare those two literals using == operator.

For example String s1=”Hello”; String s2=”Hello”; s1==s2 returns true. APPLICATION: when we come across repeated contents, this is the best option which saves memory and improves performance.

b) Creates String object. Each time JVM will create a new object for each new keyword. For example String s1 = new String(“Success”); String s2 = new String(“Success”); s1==s2 returns false.

HINT: If you want to create a new string object using second case and also you don't want a new object, then you can use intern() method to get the same object.

String s1 = "hello";

String s2 = new String("hello").intern();

System.out.println(s1 == s2);

In this case instead of creating a new object, JVM will return the same reference s. So the output will be true.

56. What will happen to the Exception object after exception handling?

It will become eligible for garbage collection and will be destroyed soon by Garbage Collector and the memory will be freed.

57. *What will be the result of compiling the following code?

public class Sample{

public static void main (String args []){

int age;

age = age + 1;

System.out.println("The age is " + age);

}

a. Compiles and runs with no output

b. Compiles and runs printing out The age is 1

c. Compiles but generates a runtime error

d. Does not compile

Choose the most appropriate answer.

58. *What does the zero^th element of the String array passed to the public static void main method contain?

a. The name of the program

b. The number of arguments

c. The first argument if one is present

Choose the most appropriate answer.

59. *Which of these is the correct format to be used to create the literal char value a?

a. ‘a’

b. "a"

c. new Character(a)

d. \000a

Choose the most appropriate answer.

60. *Which of the following is illegal?

a. int i = 32;

b. float f = 45.0;

c. double d = 45.0;

Choose the most appropriate answer.

61. * Which of the following return true?

a. "Ram" == "Ram"

b. "Ram".equals("Ram")

c. "Ram".equals(new String("Ram"))

Select all the correct answers.

62. *Which of the following do not lead to a runtime error?

a. "Ashok" + " is " + " here"

b. "We" + 3

c. 3 + 5

d. 5 + 5.5

Select all the correct answers.

63. * Which of the following are acceptable?

a. Object o = new Button("START");

b. Boolean flag = true;

c. Panel p = new Frame();

d. Frame f = new Panel();

e. Panel p = new Applet();

Select all the correct answers

64. *What is the result of compiling and running the following code?

public class Sample{

static int total = 10; //LINE2

public static void main (String args []){

new Sample();

}

public Sample(){

System.out.println("In Sample");

System.out.println(this);

int temp = this.total; //LINE9

if (temp > 5){

System.out.println(temp);

}

a. The class will not compile

b. The compiler reports an error at line 2

c. The compiler reports an error at line 9

d. The value 10 is printed to the standard output

e. The class compiles but generates a runtime error

Choose the most appropriate answer.

65. *Which of the following is correct?

a. String temp [] = new String {"t" "e" "a" };

b. String temp [] = { "e" "a" "t"};

c. String temp = {"a", "t", "e"};

d. String temp [] = {"a", "b", "c"};

Choose the most appropriate answer.

66. *Under what situations do you obtain a default constructor?

a. When you define any class

b. When the class has no other constructors

c. When you define at least one constructor

Choose the most appropriate answer.

67. *Which of the following are acceptable to the Java compiler?

a. if (2 == 3) System.out.println("Hi");

b. if (2 = 3) System.out.println("Hi");

c. if (true) System.out.println("Hi");

d. if (2 != 3) System.out.println("Hi");

e. if (myStr.equals("hello")) System.out.println("Hi");

Select all the correct answers.

68. * What is the result of executing the following code, using the parameters 4 and 0?

public void divide(int a, int b){

try{

int c = a / b;

}

catch (Exception e){

System.out.print("Exception ");

}

finally{

System.out.println("Finally");

}

a. Prints out: Exception Finally

b. Prints out: Finally

c. Prints out: Exception

d. No output

Choose the most appropriate answer.

69. *In the following code, which is the earliest statement, where the object originally held in e, may be garbage collected?

1. public class Test{

2. public static void main (String args []){

3. Employee e = new Employee("Raj", 44);

4. e.calculatePay();

5. System.out.println(e.printDetails());

6. e = null;

7. e = new Employee("Ram", 26);

8. e.calculatePay();

9. System.out.println(e.printDetails());

10. }

11. }

a. Line 10

b. Line 11

c. Line 7

d. Line 8

e. Never

Choose the most appropriate answer.

70. Which of the following layout managers honors the preferred size of a component?

a. CardLayout

b. FlowLayout

c. BorderLayout

d. GridLayout

Choose the most appropriate answer.

71. *Consider the following example:

class First{

public First (String s){

System.out.println(s);

}

public class Second extends First{

public static void main(String args []){

new Second();

}

What is the result of compiling and running the Second class?

a. Nothing happens

b. A string is printed to the standard out

c. An instance of the class First is generated

d. An instance of the class Second is created

e. An exception is raised at runtime stating that there is no null parameter constructor in class First

f. The class second will not compile as there is no default constructor in the class First

Choose the most appropriate answer.

72. *Consider the following class:

public class Test{

public static void test(){

this.print();

}

public static void print(){

System.out.println("Test");

}

public static void main(String args []){

test();

}

What is the result of compiling and running this class?

a. The string Test is printed to the standard output.

b. A runtime exception is raised stating that an object has not been created.

c. Nothing is printed to the standard output.

d. An exception is raised stating that the method test cannot be found.

e. The class fails to compile stating that the variable this cannot be referenced inside a static method.

Choose the most appropriate answer.

73. * Examine the following class definition:

public class Test{

public static void test(){

print();

}

public static void print(){

System.out.println("Test");

}

public void print(){

System.out.println("Another Test");

}

What is the result of compiling this class?

a. A successful compilation.

b. A warning stating that the class has no main method.

c. An error stating that there is a duplicated method.

d. An error stating that the method test() will call one or other of the print() methods.

Choose the most appropriate answer.

74. *Given the following sequence of Java statements

1. StringBuffer sb = new StringBuffer("abc");

2. String s = new String("abc");

3. sb.append("def");

4. s.append("def");

5. sb.insert(1, "zzz");

6. s.concat(sb);

7. s.trim();

Which of the following statements are true?

a. The compiler would generate an error for line 1.

b. The compiler would generate an error for line 2.

c. The compiler would generate an error for line 3.

d. The compiler would generate an error for line 4.

e. The compiler would generate an error for line 5.

f. The compiler would generate an error for line 6.

g. The compiler would generate an error for line 7.

Select all the correct answers.

75. *Carefully examine the following class:

public class Sample{

public static void main(String args []){

/*This is the start of a comment

if (true){

Sample obj = new Sample();

System.out.println("Done the test");

}

/* This is another comment */

System.out.println ("The end");

}

What is the result:

a. Prints out "Done the test" and nothing else.

b. Program produces no output but terminates correctly.

c. Program does not terminate.

d. The program will not compile.

e. The program generates a runtime exception.

f. The program prints out "The end" and nothing else.

g. The program prints out "Done the test" and "The end".

Choose the most appropriate answer.

76. Can we add the same Component to more than one Container?

Each GUI component can be contained only once. If a component is already in a container and you try to add it to another container, the component will be removed from the first container and then added to the second.

77. You can create a String object as String s = "abc"; Why can’t a Button object be created as Button b = "abc"?

The main reason you cannot create a button by Button b= “abc”; is because “abc” is a String literal and b is a Button object. The only object in Java that can be assigned a literal String is java.lang.String. Important to note that you are NOT calling a java.lang.String constructor, when you type String s = “abc”;

78. What is a native method?

A native method is a Java method (either an instance method or a class method) whose implementation is written in another programming language such as C.

79. What are all can be referenced by this variable?

Within an instance method or a constructor, this is a reference to the current object — the object whose method or constructor is being called. You can refer to any member of the current object from within an instance method or a constructor by using this.

80. Can a .java file contain more than one java classes?

Yes, a .java file can contain more than one java classes. But there are two restrictions:

•A .java source file can contain at most one top-level class defined by the public modifier.

•The .java file name must be the same as the public class name.

Tags : Amazon Interview Papers , Amazon Placement Papers , Amazon Interview Question , Amazon Interview JAVA Questions , Amazon Interview , Amazon Interview Papers , Amazon Placement Papers , Amazon Interview Question , Amazon Interview JAVA Questions , Amazon Interview , Google Interview Papers , Google Placement Papers , Google Interview Question , Google Interview JAVA Questions , Google Interview , Google Interview Papers , Google Placement Papers , Google Interview Question , Google Interview JAVA Questions , Google Interview , Microsoft Interview Papers , Microsoft Placement Papers , Microsoft Interview Question , Microsoft Interview JAVA Questions , Microsoft Interview , Microsoft Interview Papers , Microsoft Placement Papers , Microsoft Interview Question , Microsoft Interview JAVA Questions , Microsoft Interview , TCS Interview Papers , TCS Placement Papers , TCS Interview Question , TCS Interview JAVA Questions , TCS Interview , TCS Interview Papers , TCS Placement Papers , TCS Interview Question , TCS Interview JAVA Questions , TCS Interview , Wipro Interview Papers , Wipro Placement Papers , Wipro Interview Question , Wipro Interview JAVA Questions , Wipro Interview , Wipro Interview Papers , Wipro Placement Papers , Wipro Interview Question , Wipro Interview JAVA Questions , Wipro Interview , HCL Interview Papers , HCL Placement Papers , HCL Interview Question , HCL Interview JAVA Questions , HCL Interview , HCL Interview Papers , HCL Placement Papers , HCL Interview Question , HCL Interview JAVA Questions , HCL Interview , Zoho Interview Papers , Zoho Placement Papers , Zoho Interview Question , Zoho Interview JAVA Questions , Zoho Interview , Zoho Interview Papers , Zoho Placement Papers , Zoho Interview Question , Zoho Interview JAVA Questions , Zoho Interview , Accenture Interview Papers , Accenture Placement Papers , Accenture Interview Question , Accenture Interview JAVA Questions , Accenture Interview , Accenture Interview Papers , Accenture Placement Papers , Accenture Interview Question , Accenture Interview JAVA Questions , Accenture Interview , Infosys Interview Papers , Infosys Placement Papers , Infosys Interview Question , Infosys Interview JAVA Questions , Infosys Interview , Infosys Interview Papers , Infosys Placement Papers , Infosys Interview Question , Infosys Interview JAVA Questions , Infosys Interview , Facebook Interview Papers , Facebook Placement Papers , Facebook Interview Question , Facebook Interview JAVA Questions , Facebook Interview , Facebook Interview Papers , Facebook Placement Papers , Facebook Interview Question , Facebook Interview JAVA Questions , Facebook Interview , Interview Papers , Placement Papers , Interview Question , Interview JAVA Questions , Interview , Interview Papers , Placement Papers , Interview Question , Interview JAVA Questions , Interview

New Way of Engineering

Follow me on Linkedin