Java Certification Practice Test: 50 Expert Java Interview Questions

Welcome to your Java Test 20 - 2024

Name

Phone

Q1. Which of the following methods are available in java.util.concurrent.ConcurrentMap in addition to the methods provided by java.util.Map?

You had to select 1 option(s)

boolean remove(Object key, Object value)

boolean remove(Object key)

V putIfAbsent(K key, V value)

Object removeIfPresent(Object key)

boolean replace(K key, V oldValue, V newValue)

None of the above.

None

Q2. Identify correct statement(s) about Java records.

You had to select 1 option(s)

A record may extend another record.

A record may extend any other non-record class.

A record may implement any number of interfaces.

A record is not allowed to contain references to other records.

Records cannot be serialized.

None

Q3. Given the following class definitions and declaration:

class A {}
class B extends A {}
class C extends B {}
class D extends C {}

D d = new D();

the expression (d instanceof A) will return true.

You had to select 1 option(s)

True

False

None

Q4. Which of the following standard functional interfaces returns void?

You had to select 1 option(s)

Supplier

Function

Predicate

Consumer

UnaryOperator

None

Q5. Which operators will always evaluate all the operands?

You had to select 2 option(s)

? :

Q6. Consider the following variable declaration within the definition of an interface:

int i = 10;

Which of the following declarations defined in a non-abstract class, is equivalent to the above?

You had to select 1 option(s)

public static int i = 10;

public final int i = 10;

public static final int i = 10;

public int i = 10;

final int i = 10;

None

Q7. Which of the following are also known as "short circuiting logical operators"?

You had to select 2 option(s)

Q8. Which of the following code fragments is/are appropriate usage(s) of generics?

You had to select 2 option(s)

Q9. Using a continue in a while loop causes the loop to break the current iteration and start the next iteration of the loop.

You had to select 1 option(s)

True

False

None

Q10. The following program will always terminate.

class Base extends Thread
{
static int k = 10;
}
class Incrementor extends Base
{
public void run()
{
for(; k>0; k++)
{
System.out.println("IRunning...");
}
}
}
class Decrementor extends Base
{
public void run()
{
for(; k>0; k--)
{
System.out.println("DRunning...");
}
}
}
public class TestClass
{
public static void main(String args[]) throws Exception
{
Incrementor i = new Incrementor();
Decrementor d = new Decrementor();
i.start();
d.start();
}
}

You had to select 1 option(s)

True

False

None

Q11. Select the correct order of restrictiveness for access modifiers...

(First one should be least restrictive)

You had to select 1 option(s)

None

Q12. Consider the following directory structure and the files contained in the directories:

c:\javatest
+-
+-
+-
+-
-- BazA.java
-- BazB.java

Assuming that the package name specified in BazA and BazB is foo.bar, which of the following statements are correct?

You had to select 1 option(s)

There should be a module-info.java file in the src directory for it to be a valid module definition.

The root directory of a source module definition must have module-info.java.

There should be a module-info.java file in the foo.bar directory for it to be a valid source module definition.

There should be a module.java file in the foo directory for it to be a valid module definition.

There should be a module-info.java file in the bar directory for it to be a valid source module definition.

There should be a module.java file in the foo.bar directory for it to be a valid module definition.

None

Q13. Identify true statements about sealed classes.

You had to select 1 option(s)

Only an abstract class or an interface can be sealed.

Only top level classes can be sealed.

A sealed class cannot be final.

All reference types - classes, interfaces, enums, and records - can be marked as sealed.

None of the above.

None

Q14. Which one of these is a valid definition of a class TestClass that cannot be sub-classed?

You had to select 1 option(s)

final class TestClass { }

abstract class TestClass { }

native class TestClass { }

static class TestClass { }

private class TestClass { }

sealed class TestClass permits Object{ }

None

Q15. The following code snippet will not compile:

var i = 10;
System.out.println( i<20 ? out1() : out2() );

Assume that out1 and out2 methods have the following signatures: public void out1(); and public void out2();

You had to select 1 option(s)

True

False

None

Q16. You have been given an instance of an Executor and you use that instance to execute tasks. How many threads will be created for executing these tasks by the Executor?

You had to select 1 option(s)

Exactly 1.

One thread for each task that is submitted to the Executor.

As many as there are cores in the CPU.

Number of threads created by the Executor depends on how the Executor instance was created.

Number of threads is automatically determined based on the load on the Executor instance.

None

Q17. Which of these statements are true?

You had to select 3 option(s)

Non-static inner class cannot have static members.

Objects of static nested classes can be created without creating instances of their Outer classes.

Member variables in any nested class cannot be declared final.

Anonymous classes cannot define constructors explicitly in Java code.

Anonymous classes cannot be static.

Q18. How will you initialize a SimpleDateFormat object so that the following code will print the full name of the month of the given date?

System.out.println(sdf.format(new Date()));

Note: Although this SimpleDateFormat is not mentioned explicitly in the exam objectives, it is used a lot in legacy code. Read about this class if you have time. Otherwise, leave it.

You had to select 1 option(s)

SimpleDateFormat sdf = new SimpleDateFormat("MMMM", Locale.FRANCE);

SimpleDateFormat sdf = new SimpleDateFormat("M*", Locale.FRANCE);

SimpleDateFormat sdf = new SimpleDateFormat("mmmm", Locale.FRANCE);

SimpleDateFormat sdf = new SimpleDateFormat("mmm", Locale.FRANCE);

SimpleDateFormat sdf = new SimpleDateFormat("MM", Locale.FRANCE);

None

Q19. In which of these variable declarations, will the variable remain uninitialized unless explicitly initialized?

You had to select 1 option(s)

Declaration of an instance variable of type int.

Declaration of a static class variable of type float.

Declaration of a local variable of type float.

Declaration of a static class variable of class Object

Declaration of an instance variable of class Object.

None

Q20. Which variables of the encapsulating class can an inner class access, if the inner class is defined in an instance method of the encapsulating class?

You had to select 4 option(s)

All static variables

All final instance variables

All instance variables

All automatic variables.

All final and effectively final automatic variables

Q21. Which of the following are valid declarations in a class?

You had to select 1 option(s)

abstract int absMethod(int param) throws Exception;

abstract native int absMethod(int param) throws Exception;

float native getVariance() throws Exception;

abstract private int absMethod(int param) throws Exception;

None

Q22. In the following code what will be the output if 0 (integer value zero) is passed to loopTest()?

public class TestClass{
public void loopTest(int x){
loop: for (var i = 1; i < 5; i++){
for (var j = 1; j < 5; j++){
System.out.println(i);
if (x == 0) { continue loop; }
System.out.println(j);
}
}
}
}

You had to select 1 option(s)

The program will not compile.

It will print 1 2 3 4

It will print 1 1 2 3 4

It will print 1 1 2 2 3 3 4 4

Produces no output

None

Q23. What will be the output of the following program (excluding the quotes)?

public class SubstringTest{
public static void main(String args[]){
String String = """
string isa
string""";
System.out.println(String.substring(3, 6));
}
}

You had to select 1 option(s)

It will not compile.

"ing is"

"ing isa"

"ing " (There is a space after g)

None of the above.

None

Q24. Consider the following program...

public class TestClass implements Runnable
{
int x = 0, y = 0;
public void run()
{
while(true)
{
x++; y++;
System.out.println(" x = "+x+" , y = "+y);
}
}
public static void main(String[] args)
{
TestClass tc = new TestClass();
new Thread(tc).start();
new Thread(tc).start();
}
}

You had to select 1 option(s)

It will throw exception at run time because two threads cannot be created from the same object.

It will keep on printing values which show x and y always as equal and increasing by 1 at each line.

It will keep on printing values which show x and y always as different.

Nothing can be said about the sequence of the values that will be printed.

It will keep on printing values which show x and y always as equal but may increase more than 1 at each line.

None

Q25. What can be the type of a catch argument?

(Select the best option.)

You had to select 1 option(s)

Any class that extends java.lang.Exception

Any class that extends java.lang.Exception except any class that extends java.lang.RuntimeException

Any class that is-a Throwable.

Any Object

Any class that extends Error

None

Q26. Identify correct statements about Java Date and Time API.

You had to select 1 option(s)

Classes used to represent dates and times in java.time package are thread safe.

Time zone is an integral part of all classes in java.time package.

Period class is ideal for usage as a time stamp.

Duration class handles day light saving time changes.

You can create instances of Instant using one of the several constructors that take date, time, or date time values.

None

Q27. Which statements concerning the relation between a non-static inner class and its outer class instances are true?

You had to select 3 option(s)

Member variables of the outer instance are always accessible to inner instances, regardless of their accessibility modifiers.

Member variables of the outer instance can always be referred to using only the variable name within the inner instance.

More than one inner instance can be associated with the same outer instance.

An inner class can extend its outer class.

A final outer class cannot have any inner classes.

Q28. A try-with-resources statement requires ......

You had to select 1 option(s)

a catch block.

a finally block.

either a catch block or a finally block.

neither a catch block nor a finally block.

None

Q29. If a synchronized method ends up throwing an exception to the caller, the lock acquired by the thread associated with this method due to the usage of the synchronized keyword is released automatically.

You had to select 1 option(s)

True

False

None

Q30. In Java, Strings are immutable. A direct implication of this is...

You had to select 2 option(s)

You cannot call methods like "1234".replace('1', '9'); and expect to change the original String.

You cannot change a String object, once it is created.

You can change a String object only by the means of its methods.

You cannot extend String class.

You cannot compare String objects.

Q31. An abstract method cannot be overridden.

You had to select 1 option(s)

True

False

None

Q32. Anonymous inner classes always extend directly from the Object class.

You had to select 1 option(s)

True

False

None

Q33. Which of these statements concerning the charAt() method of the String class are true?

You had to select 2 option(s)

The charAt( ) method can take a char value as an argument.

The charAt( ) method returns a Character object.

The expression char ch = "12345".charAt(3) will assign 3 to ch.

The expression char ch = str.charAt(str.length()) where str is "12345", will assign 3 to ch.

The index of the first character is 0.

It throws StringIndexOutOfBoundsException if passed a value higher than or equal to the length of the string (or less than 0).

It throws ArrayIndexOutOfBoundsException if passed a value higher than or equal to the length of the string (or less than 0).

Q34. Identify the correct statements:

You had to select 1 option(s)

A CallableStatement is used to call a stored procedure in the database while a PreparedStatement is used to call a stored function.

A CallableStatement is easier to build and call from JDBC code than a PreparedStatement.

A CallableStatement is preferred over PreparedStatement because it supports long running transactions.

A CallableStatement is preferred over Statement because it supports long running transactions.

None

Q35. Identify correct statements regarding System.out.

You had to select 2 option(s)

It is of type java.io.OutputStream.

It refers to the standard output stream of the program and is opened when the program tries to write to the console for the first time.

An important feature of the stream referred to by System.out is that it never throws IOException when data is written to it.

All characters printed by a System.out are converted into bytes using the given encoding or charset, or platform's default character encoding if not specified.

Since it refers to the standard output stream of the program and it cannot be closed by the program.

Q36. Which interfaces does java.util.NavigableMap extend directly or indirectly?

You had to select 2 option(s)

java.util.SortedSet

java.util.Map

java.util.SortedMap

java.util.TreeMap

java.util.List

Q37. You are modeling a class hierarchy for living things. You have a class LivingThing which has an abstract method reproduce().

Now, you want to have 2 concrete subclasses of LivingThing - Plant and Animal. Both do reproduce but the mechanisms are different. What would you do?

You had to select 1 option(s)

Overload the reproduce method in Plant and Animal classes

Overload the reproduce method in LivingThing class.

Override the reproduce method in Plant and Animal classes

Either overload or override reproduce in Plant and Animal classes, it depends on the preference of the designer.

None

Q38. Which of these statements are valid when occurring by themselves in a method?

You had to select 3 option(s)

while ( ) break ;

do { break ; } while (true) ;

if (true) { break ; } (When not inside a switch block or a loop)

switch (1) { default : break; }

for ( ; true ; ) break ;

switch (1) { default -> break; }

Q39. How many methods have to be provided by a class that is not abstract and that says it implements Serializable interface?

You had to select 1 option(s)

None

Q40. Identify the correct statement regarding a JDBC Connection:

You had to select 1 option(s)

When a JDBC Connection is created, it is in auto-commit mode.

When a JDBC Connection is created, its commit mode depends on the parameters used while creating the connection.

When a JDBC Connection is created, its auto-commit feature is disabled.

When a JDBC Connection is created, its commit mode is undetermined.

None

Q41. Which of the following statements are true?

You had to select 2 option(s)

Private methods cannot be overridden in subclasses.

A subclass can override any method in a non-final superclass.

An overriding method can declare that it throws a wider spectrum of checked exceptions than the method it is overriding.

The parameter list of an overriding method must be a subset of the parameter list of the method that it is overriding.

The overriding method may opt not to declare any throws clause even if the original method has a throws clause.

Q42. Which of the following is not a primitive data value in Java?

You had to select 3 option(s)

"x"

'x'

10.2F

Object

false

Instance of a record.

Q43. What will be the result of attempting to compile a java source file TopClass.java containing all the following code?

package test;

public class TopClass
{
public Inner inner1 = new Inner()
{
private static int value;
public void doA(){ System.out.println("doing A"); }
};

public void doA() { inner1.doA(); }
}

class Inner
{
int value;
}

You had to select 1 option(s)

The class will fail to compile because the class Inner has not been declared before being referenced in class TopClass.

The class will fail to compile because inner is a keyword.

The class will fail to compile, since the class Inner must be defined in a file called Inner.java

The classes will compile.

The class will fail to compile because inner class cannot have a static field.

None of these.

None

Q44. Which of the following methods modify the object on which they are called?

You had to select 1 option(s)

setValue(int, String)of java.lang.String class.

The substring(int) method of the java.lang.String class

The replace() method of the java.lang.String class.

The reverse() method of the StringBuilder class.

None of these.

None

Q45. Which of the following collection implementations are thread-safe?

You had to select 1 option(s)

ArrayList

HashSet

HashMap

TreeSet

None of the Above.

None

Q46. Consider the following program.

public class TestClass implements Runnable
{
volatile int x;
public void run(){ x = 5; }

public static void main(String[] args)
{
TestClass tc = new TestClass();
tc.x = 10;
new Thread(tc).start(); // 1
System.out.println(tc.x);
}

}

What will it print when run?

You had to select 1 option(s)

It will not compile.

Exception at Runtime.

The output cannot be determined.

None

Q47. Identify correct statement(s) regarding a switch statement written using the new arrow syntax.

You had to select 2 option(s)

It has the same "fall through" behavior that the regular switch statement has.

It must return a value.

It is possible to use a break statement in a case block.

Multiple values may be specified in a single case statement.

It must have a default label.

Q48. What will be the result of attempting to compile and run the following class?

public class IfTest{
public static void main(String args[]){
if (true)
if (false)
System.out.println("True False");
else
System.out.println("True True");
}
}

You had to select 1 option(s)

The code will fail to compile because the syntax of the if statement is not correct.

The code will fail to compile because the values in the condition bracket are invalid.

The code will compile correctly and will not display anything.

The code will compile correctly and will display True True.

The code will compile correctly but will display True False

None

Q49. You want to execute your tasks after a given delay. Which ExecutorService would you use?

You had to select 1 option(s)

FixedDelayExecutorService

TimedExecutorService

DelayedExecutorService

ScheduledExecutorService

None

Q50. What will the following program print?

interface Flyer{
}

class AirPlane implements Flyer{
}

public class TestClass {

static void flyIt(Flyer f){
System.out.println("Flyer Flying");
}

static void flyIt(AirPlane a){
System.out.println("AirPlane Flying");
}

public static void main(String[] args){
Flyer f = new AirPlane();
AirPlane a = new AirPlane();
flyIt(f); //1
flyIt(a); //2
}
}

You had to select 1 option(s)

Flyer Flying
AirPlane Flying

AirPlane Flying
AirPlane Flying

Flyer Flying
Flyer Flying

Line marked //1 will fail to compile.

Line marked //2 will fail to compile.

Both the lines marked //1 and //2 will fail to compile.

None

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