OCPJP 6 Free Mock Exam Practice Questions

8/11/2019 OCPJP 6 Free Mock Exam Practice Questions

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OCPJP 6 Free Mock Exam Practice Questions

Questions no -1What is the output for the below code ?

class A implements Runnable{public void run(){

System.out.println(Thread.currentThread().getName());}

}

public class Test {public static void main(String... args) {

A a = new A();Thread t = new Thread(a);Thread t1 = new Thread(a);

t.setName("t");t1.setName("t1");t.setPriority(10);t1.setPriority(-3);t.start();t1.start();

}}

Options are

A.t t1B.t1 t

C.t t

D.Compilation succeed but Runtime Exception

Answer :

D is the correct answer.

Thread priorities are set using a positive integer, usually between 1 and 10.

t1.setPriority(-3); throws java.lang.IllegalArgumentException.

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class A implements Runnable{public void run(){

System.out.println(Thread.currentThread().getName());}

}

1. public class Test {2. public static void main(String... args) {3. A a = new A();4. Thread t = new Thread(a);5. t.setName("good");6. t.start();

7. }8. }

Options are

A.goodB.null

C.Compilation fails with an error at line 5D.Compilation succeed but Runtime Exception

Answer :

A is the correct answer.

Thread.currentThread().getName() return name of the current thread.

Questions no -3
https://play.google.com/store/apps/details?id=com.bricksbay.exam.ocpjp6f


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What is the output for the below code ?

public class Test {

public static void main(String[] args) {

Boolean expr = true;if (expr) {System.out.println("true");

} else {System.out.println("false");

}

}

}

optionsA)trueB)Compile Error - can't use Boolean object in if().C)falseD)Compile Properly but Runtime Exception.

Correct answer is : A

Explanations : In the if statement, condition can be Boolean objectin jdk1.5 and jdk1.6.In the previous version only boolean is allowed.


public class Test {

public static void main(String[] args) {List list = new ArrayList();list.add(0, 59);int total = list.get(0);System.out.println(total);

}

}

options


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A)59B)Compile time error, because you have to do int total =((Integer)(list.get(0))).intValue();C)Compile time error, because can't add primitive type in List.D)Compile Properly but Runtime Exception.


Explanations :Manual conversion between primitive types (such as anint) and wrapper classes

(such as Integer) is necessary when adding a primitive data type to acollection in jdk1.4 but

The new autoboxing/unboxing feature eliminates this manual conversionin jdk 1.5 and jdk 1.6.


public class Test {

public static void main(String[] args) {Integer i = null;int j = i;System.out.println(j);

}

}

optionsA)0B)Compile with errorC)nullD)NullPointerException

Correct answer is : D

Explanations :An Integer expression can have a null value. If yourprogram tries to autounbox null,

it will throw a NullPointerException.Questions no -4What is the output for the below code ?

public class Outer {private int a = 7;

class Inner {public void displayValue() {


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System.out.println("Value of a is " + a);}

}}

public class Test {

public static void main(String... args) throws Exception {Outer mo = new Outer();Outer.Inner inner = mo.new Inner();inner.displayValue();

}

}

optionsA)Value of a is 7B)Compile Error - not able to access private member.C)Runtime ExceptionD)Value of a is 8


Explanations : An inner class instance can never stand alone withouta direct relationship to an instance of the outer class.

you can access the inner class is through a live instance of the

outer class.

Inner class can access private member of the outer class.


public class B {

public String getCountryName(){return "USA";

}

public StringBuffer getCountryName(){StringBuffer sb = new StringBuffer();sb.append("UK");return sb;

}

public static void main(String[] args){B b = new B();


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System.out.println(b.getCountryName().toString());}

}

optionsA)Compile with errorB)USAC)UKD) Runtime Exception


Explanations : You cannot have two methods in the same class withsignatures that only differ by return type.Questions no -6What is the output for the below code ?

public class C {

}

public class D extends C{

}

public class A {

public C getOBJ(){System.out.println("class A - return C");

return new C();

}

}

public class B extends A{

public D getOBJ(){System.out.println("class B - return D");return new D();

}

}

public class Test {

public static void main(String... args) {A a = new B();a.getOBJ();


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}}

options

A)Compile with error - Not allowed to override the return type of amethod with a subtype of the original type.B)class A - return CC)class B - return DD) Runtime Exception

Correct answer is : C

Explanations : From J2SE 5.0 onwards. You are now allowed to overridethe return type of a method with a subtype of the original type.Questions no -7What is the output for the below code ?

public class A {

public String getName() throws ArrayIndexOutOfBoundsException{return "Name-A";

}

}

public class C extends A{

public String getName() throws Exception{return "Name-C";

}

}


A a = new C();a.getName();

}

}

optionsA)Compile with errorB)Name-AC)Name-CD)Runtime Exception



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Explanations : Exception Exception is not compatible with throwsclause in A.getName().

Overridden method should throw only same or sub class of theexception thrown by super class method.Questions no -8


import java.util.regex.Matcher;import java.util.regex.Pattern;

public class Test {

public static void main(String... args) {

Pattern p = Pattern.compile("a*b");Matcher m = p.matcher("b");boolean b = m.matches();System.out.println(b);

}}

optionsA)trueB)Compile ErrorC)false

D)b


Explanations : a*b means "a" may present zero or more time and "b"should be present once.Questions no -9What is the output for the below code ?

public class Test {


String input = "1 fish 2 fish red fish blue fish";Scanner s = new

Scanner(input).useDelimiter("\\s*fish\\s*");System.out.println(s.nextInt());System.out.println(s.nextInt());System.out.println(s.next());System.out.println(s.next());s.close();


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}}

optionsA)1 2 red blueB)Compile Error - because Scanner is not defind in java.C)1 fish 2 fish red fish blue fishD)1 fish 2 fish red blue fish


Explanations : java.util.Scanner is a simple text scanner which canparse primitive types and strings using regular expressions.Questions no -10


public class Test {


Pattern p = Pattern.compile("a{3}b?c*");Matcher m = p.matcher("aaab");boolean b = m.matches();System.out.println(b);

}}

optionsA)trueB)Compile ErrorC)falseD)NullPointerException


Explanations :X? X, once or not at allX* X, zero or more timesX+ X, one or more timesX{n} X, exactly n timesX{n,} X, at least n timesX{n,m} X, at least n but not more than m timesQuestions no -11


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public class Test {


Pattern p = Pattern.compile("a{1,3}b?c*");Matcher m = p.matcher("aaab");boolean b = m.matches();System.out.println(b);

}}

optionsA)trueB)Compile ErrorC)falseD)NullPointerException


Explanations :X? X, once or not at allX* X, zero or more timesX+ X, one or more timesX{n} X, exactly n times

X{n,} X, at least n timesX{n,m} X, at least n but not more than m timesQuestions no -12What is the output for the below code ?

public class A {public A() {System.out.println("A");

}}

public class B extends A implements Serializable {public B() {

System.out.println("B");}

}

public class Test {

public static void main(String... args) throws Exception {B b = new B();


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ObjectOutputStream save = new ObjectOutputStream(new

FileOutputStream("datafile"));save.writeObject(b);save.flush();

ObjectInputStream restore = new ObjectInputStream(newFileInputStream("datafile"));

B z = (B) restore.readObject();

}

}

optionsA)A B AB)A B A BC)B BD)A B


Explanations :On the time of deserialization , the Serializableobject not create new object. So constructor of class B does notcalled.

A is not Serializable object so constructor is called.Questions no -13What is the output for the below code ?

public class A {}

public class B implements Serializable {A a = new A();public static void main(String... args){

B b = new B();try{

FileOutputStream fs = newFileOutputStream("b.ser");

ObjectOutputStream os = newObjectOutputStream(fs);

os.writeObject(b);os.close();

}catch(Exception e){e.printStackTrace();

}


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}

}

optionsA)Compilation FailB)java.io.NotSerializableException: Because class A is notSerializable.C)Run properlyD)Compilation Fail : Because class A is not Serializable.

Correct answer is : B

Explanations :It throws java.io.NotSerializableException:A Becauseclass A is not Serializable.

When JVM tries to serialize object B it will try to serialize A alsobecause (A a = new A()) is instance variable of Class B.

So thows NotSerializableException.

Questions no -14What is the output for the below code running in the same JVM?

public class A implements Serializable {transient int a = 7;static int b = 9;

}

public class B implements Serializable {

public static void main(String... args){A a = new A();try {

ObjectOutputStream os = new ObjectOutputStream(new FileOutputStream("test.ser"));

os.writeObject(a);os. close();System.out.print( + + a.b + " ");

ObjectInputStream is = new ObjectInputStream(new

FileInputStream("test.ser"));A s2 = (A)is.readObject();is.close();System.out.println(s2.a + " " + s2.b);

} catch (Exception x){

x.printStackTrace();}


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}

}

optionsA)9 0 9B)9 7 9C)0 0 0D)0 7 0


Explanations :transient variables are not serialized when an objectis serialized.

In the case of static variable you can get the values in the same

JVM.


public enum Test {BREAKFAST(7, 30), LUNCH(12, 15), DINNER(19, 45);

private int hh;

private int mm;

Test(int hh, int mm) {

assert (hh >= 0 && hh = 0 && mm


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optionsA)7:30B)Compile Error - an enum cannot be instantiated using the newoperator.C)12:50

D)19:45


Explanations : As an enum cannot be instantiated using the newoperator, the constructors cannot be called explicitly.You have to do likeTest t = BREAKFAST;Questions no -16What is the output for the below code ?

public class Test {enum Day {

MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY,SUNDAY}enum Month {

JAN, FEB}

public static void main(String[] args) {

int[] freqArray = { 12, 34, 56, 23, 5, 13, 78 };

// Create a Map of frequenciesMap ordinaryMap = new HashMap();for (Day day : Day.values()) {

ordinaryMap.put(day, freqArray[day.ordinal()]);}

// Create an EnumMap of frequenciesEnumMap frequencyEnumMap = new

EnumMap(ordinaryMap);

// Change some frequenciesfrequencyEnumMap.put(null, 100);

System.out.println("Frequency EnumMap: " +frequencyEnumMap);

}

}


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optionsA)Frequency EnumMap: {MONDAY=12, TUESDAY=34, WEDNESDAY=56,THURSDAY=23, FRIDAY=5, SATURDAY=13, SUNDAY=78}B)Compile ErrorC)NullPointerExceptionD)Frequency EnumMap: {MONDAY=100, TUESDAY=34, WEDNESDAY=56,

THURSDAY=23, FRIDAY=5, SATURDAY=13, SUNDAY=123}


Explanations : The null reference as a key is NOT permitted.Questions no -17public class EnumTypeDeclarations {

public void foo() {

enum SimpleMeal {BREAKFAST, LUNCH, DINNER

}

}}

Is the above code Compile without error ?

optionsA)Compile without errorB)Compile with errorC)Compile without error but Runtime ExceptionD)Compile without error but Enum Exception


Explanations :An enum declaration is a special kind of class declaration:

a) It can be declared at the top-level and as static enumdeclaration.

b) It is implicitly static, i.e. no outer object is associated withan enum constant.

c) It is implicitly final unless it contains constant-specific classbodies, but it can implement interfaces.

d) It cannot be declared abstract unless each abstract method isoverridden in the constant-specific class body of every enumconstant.

e) Local (inner) enum declaration is NOT OK!

Here inpublic void foo() {


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enum SimpleMeal {BREAKFAST, LUNCH, DINNER

}}

enum declaration is local within method so compile time error.


public enum Test {int t;BREAKFAST(7, 30), LUNCH(12, 15), DINNER(19, 45);

private int hh;

private int mm;

Test(int hh, int mm) {assert (hh >= 0 && hh = 0 && mm


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public class B extends Thread{public static void main(String argv[]){

B b = new B();b.run();}public void start(){for (int i = 0; i < 10; i++){System.out.println("Value of i = " + i);}}}

optionsA)A compile time error indicating that no run method is defined forthe Thread classB)A run time error indicating that no run method is defined for theThread classC)Clean compile and at run time the values 0 to 9 are printed outD)Clean compile but no output at runtime


Explanations : This is a bit of a sneaky one as I have swapped aroundthe names of the methods you need to define and call when running athread.

If the for loop were defined in a method called public void run()and the call in the main method had been to b.start() The list ofvalues from 0 to 9would have been output.Questions no -20


public class Test extends Thread{

static String sName = "good";public static void main(String argv[]){

Test t = new Test();

t.nameTest(sName);System.out.println(sName);

}public void nameTest(String sName){

sName = sName + " idea ";start();

}public void run(){


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for(int i=0;i < 4; i++){

sName = sName + " " + i;

}}

}

optionsA)goodB)good ideaC)good idea good ideaD)good 0 good 0 1


Explanations : Change value in local methods wouldnt change inglobal in case of String ( because String object is immutable).Questions no -21What is the output for the below code ?

public class Test{public static void main(String argv[]){Test1 pm1 = new Test1("One");pm1.run();Test1 pm2 = new Test1("Two");pm2.run();

}}

class Test1 extends Thread{private String sTname="";Test1(String s){

sTname = s;

}public void run(){

for(int i =0; i < 2 ; i++){try{sleep(1000);

}catch(InterruptedException e){}

yield();System.out.println(sTname);}

}}


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optionsA)Compile errorB)One One Two Two

C)One Two One TwoD)One Two


Explanations : If you call the run method directly it just acts asany other method and does not return to the calling code until it hasfinished. executingQuestions no -22What is the output for the below code ?

public class Test extends Thread{public static void main(String argv[]){

Test b = new Test();b.start();}public void run(){

System.out.println("Running");}

}

optionsA)Compilation clean and run but no output

B)Compilation and run with the output "Running"C)Compile time error with complaint of no Thread importD)Compile time error with complaint of no access to Thread package


Explanations :The Thread class is part of the core java.lang package and does notneed any explicit import statement.Questions no -23What is the output for the below code ?

public class Tech {

public void tech() {System.out.println("Tech");

}

}

public class Atech {


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Tech a = new Tech() {public void tech() {

System.out.println("anonymous tech");}

};

public void dothis() {a.tech();

}

public static void main(String... args){Atech atech = new Atech();atech.dothis();

}

optionsA)anonymous techB)Compile ErrorC)TechD)anonymous tech Tech


Explanations : This is anonymous subclass of the specified classtype.

Anonymous inner class ( anonymous subclass ) overriden the Tech superclass of tech() method.

Therefore Subclass method will get called.Questions no -24What is the output for the below code ?

public class Outer {private String x = "Outer variable";void doStuff() {String z = "local variable";class Inner {public void seeOuter() {System.out.println("Outer x is " + x);System.out.println("Local variable z is " + z);

}}

}

}


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optionsA)Outer x is Outer variable.B)Compile ErrorC)Local variable z is local variable.D)Outer x is Outer variable Local variable z is local variable


Explanations : Cannot refer to a non-final variable z inside an innerclass defined in a different method.Questions no -25


public class Test {

public static void main(String... args) {for(int i = 2; i < 4; i++)

for(int j = 2; j < 4; j++)assert i!=j : i;

}}

optionsA)The class compiles and runs, but does not print anything.B)The number 2 gets printed with AssertionErrorC)The number 3 gets printed with AssertionErrorD)compile error


Explanations : When i and j are both 2, assert condition is false,and AssertionError gets generated.Questions no -26


public class Test {

public static void main(String... args) {for(int i = 2; i < 4; i++)

for(int j = 2; j < 4; j++)

if(i < j)assert i!=j : i;

}}

optionsA)The class compiles and runs, but does not print anything.


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B)The number 2 gets printed with AssertionErrorC)The number 3 gets printed with AssertionErrorD)compile error


Explanations : When if condition returns true, the assert statementalso returns true.Hence AssertionError not generated.Questions no -26What is the output for the below code ?

public class NameBean {private String str;

NameBean(String str ){this.str = str;

}

public String toString() {return str;}

}

import java.util.HashSet;

public class CollClient {

public static void main(String ... sss) {HashSet myMap = new HashSet();String s1 = new String("das");String s2 = new String("das");

NameBean s3 = new NameBean("abcdef");NameBean s4 = new NameBean("abcdef");

myMap.add(s1);myMap.add(s2);myMap.add(s3);myMap.add(s4);

System.out.println(myMap);}

}

optionsA)das abcdef abcdefB)das das abcdef abcdefC)das abcdefD)abcdef abcdef



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Explanations : Need to implement 'equals' and 'hashCode' methods toget unique Set for user defind objects(NameBean).

String object internally implements 'equals' and 'hashCode' methodstherefore Set only stored one value.

Questions no -27Synchronized resizable-array implementation of the List interface is_____________?

optionsA)VectorB)ArrayListC)HashtableD)HashMap


Explanations : Vector implements List, RandomAccess - Synchronizedresizable-array implementation of the List interface with additional"legacy methods."Questions no -28What is the output for the below code ?public class Test {

public static void main(String argv[]){

ArrayList list = new ArrayList();

ArrayList listStr = list;ArrayList listBuf = list;listStr.add(0, "Hello");StringBuffer buff = listBuf.get(0);System.out.println(buff.toString());

}

}

options

A)HelloB)Compile errorC)java.lang.ClassCastExceptionD)null


Explanations : java.lang.String cannot be cast tojava.lang.StringBuffer at the code StringBuffer buff =


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listBuf.get(0);So thows java.lang.ClassCastException.Questions no -29What is the output for the below code ?

import java.util.LinkedList;

import java.util.Queue;


Queue q = new LinkedList();q.add("newyork");q.add("ca");q.add("texas");show(q);

}

public static void show(Queue q) {q.add(new Integer(11));while (!q.isEmpty ( ) )

System.out.print(q.poll() + " ");}

}

optionsA)Compile error : Integer can't addB)newyork ca texas 11C)newyork ca texasD)newyork ca


Explanations :

q was originally declared as Queue, But in show() methodit is passed as an untyped Queue. nothing in the compiler or JVMprevents us from adding an Integer after that.

If the show method signature is public static voidshow(Queue q) than you can't add Integer, Only Stringallowed. But public static void show(Queue q) is untyped Queue so youcan add Integer.

poll() Retrieves and removes the head of this queue, or returnsnull if this queue is empty.Questions no -30What is the output for the below code ?


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public interface TestInf {int i =10;}


TestInf.i=12;System.out.println(TestInf.i);

}

}

optionsA)Compile with error

B)10C)12D) Runtime Exception


Explanations : All the variables declared in interface is Implicitlystatic and final , therefore can't change the value.Questions no -31What is the output for the below code ?

public class Test {static { int a = 5; }

public static void main(String[] args){System.out.println(a);}

}

optionsA)Compile with errorB)5C)0D) Runtime Exception


Explanations : A variable declared in a static initialiser is notaccessible outside its enclosing block.Questions no -32What is the output for the below code ?

class A {{ System.out.print("b1 "); }


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public A() { System.out.print("b2 "); }}class B extends A {static { System.out.print("r1 "); }public B() { System.out.print("r2 "); }{ System.out.print("r3 "); }

static { System.out.print("r4 "); }}class C extends B {public static void main(String[] args) {System.out.print("pre ");new C();System.out.println("post ");

}}

options

A)r1 r4 pre b1 b2 r3 r2 postB)r1 r4 pre b1 b2 postC)r1 r4 pre b1 b2 post r3 r2D)pre r1 r4 b1 b2 r2 r3 post


Explanations : All static blocks execute first then blocks andconstructor.

Blocks and constructor executes (super class block then super classconstructor, sub class block then sub class constructor).

Sequence for static blocks is super class first then sub class.

Sequence for blocks is super class first then sub class.


public class Test {

public static void main(String... args) throws Exception {Integer i = 34;int l = 34;

if(i.equals(l)){System.out.println(true);

}else{System.out.println(false);

}

}

}


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optionsA)trueB)false

C)Compile ErrorD) Runtime Exception


Explanations : equals() method for the integer wrappers will onlyreturn true if the two primitive types and the two values are equal.Questions no -34Which statement is true about outer class?

options

A)outer class can only declare public , abstract and finalB)outer class may be privateC)outer class can't be abstractD)outer class can be static


Explanations : outer class can only declare public , abstract andfinal.Questions no -35


static public class Test {public static void main(String[] args) {

char c = 'a';

switch(c){case 65:

System.out.println("one");break;case 'a':

System.out.println("two");break;case 3:

System.out.println("three");}

}

}

optionsA)one


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B)twoC)Compile error - char can't be permitted in switch statementD)Compile error - Illegal modifier for the class Test; only public,abstract & final are permitted.


Explanations : outer class can only declare public , abstract andfinal.Illegal modifier for the class Test; only public, abstract & finalare permittedQuestions no -36


public class Test {


ArrayList list = new ArrayList();list.add(1);list.add(2);list.add(3);

for(int i:list)System.out.println(i);

}}

options

A)1 2 3B)Compile error , can't add primitive type in ArrayListC)Compile error on for(int i:list) , Incorrect SyntaxD)0 0 0


Explanations : JDK 1.5, 1.6 allows add primitive type in ArrayListand for(int i:list) syntax is also correct.for(int i:list) is same asfor(int i=0; i < list.size();i++){

int a = list.get(i);

}Questions no -37What is the output for the below code ?

public class SuperClass {public int doIt(String str, Integer... data)throws

ArrayIndexOutOfBoundsException{String signature = "(String, Integer[])";System.out.println(str + " " + signature);


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return 1;}

}

public class SubClass extends SuperClass{

public int doIt(String str, Integer... data) throws Exception{

String signature = "(String, Integer[])";System.out.println("Overridden: " + str + " " +

signature);return 0;

}

public static void main(String... args){

SuperClass sb = new SubClass();

try{ sb.doIt("hello", 3);}catch(Exception e){

}

}

}

options

A)Overridden: hello (String, Integer[])B)hello (String, Integer[])C)This code throws an Exception at RuntimeD)Compile with error


Explanations : Exception Exception is not compatible with throwsclause in SuperClass.doIt(String, Integer[]).The same exception or subclass of that exception is allowed.

Questions no -38What is the result of executing the following code, using the

parameters 0 and 3 ?

public void divide(int a, int b) {try {

int c = a / b;} catch (Exception e) {

System.out.print("Exception ");} finally {

System.out.println("Finally");


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}

optionsA)Prints out: Exception Finally

B)Prints out: FinallyC)Prints out: ExceptionD)Compile with error


Explanations : finally block always executed whether exception occursor not.

0/3 = 0 Does not throws exception.Questions no -39Which of the below statement is true about Error?

optionsA)An Error is a subclass of ThrowableB)An Error is a subclass of ExceptionC)Error indicates serious problems that a reasonable applicationshould not try to catch.D)An Error is a subclass of IOException

Correct answer is : A and C

Explanations : An Error is a subclass of Throwable that indicatesserious problems that a reasonable application should not try tocatch.

Questions no -40Which of the following is type of RuntimeException?

optionsA)IOExceptionB)ArrayIndexOutOfBoundsExceptionC)ExceptionD)Error


Explanations : Below is the tree.java.lang.Objectjava.lang.Throwable

java.lang.Exceptionjava.lang.RuntimeException

java.lang.IndexOutOfBoundsExceptionjava.lang.ArrayIndexOutOfBoundsException


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public class Test {

public static void main(String... args) throws Exception {

File file = new File("test.txt");System.out.println(file.exists());FileWriter fw = new FileWriter(file);System.out.println(file.exists());

}

}

optionsA)true true

B)false falseC)false trueD)true false


Explanations :Creating a new instance of the class File, you're notyet making an actual file, you're just creating a filename.

So file.exists() return false.

FileWriter fw = new FileWriter(file) do three things:

It created a FileWriter reference variable fw.

It created a FileWriter object, and assigned it to fw.

It created an actual empty file out on the disk.

So file.exists() return true.Questions no -42When comparing java.io.BufferedWriter and java.io.FileWriter, whichcapability exist as a method in only one of two ?

optionsA)closing the streamB)flushing the streamC)writting to the streamD)writting a line separator to the stream



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Explanations :A newLine() method is provided in BufferedWriter whichis not in FileWriter.Questions no -43What is the output for the below code ?public class Test{

public static void main(String[] args) {int i1=1;switch(i1){

case 1:System.out.println("one");

case 2:System.out.println("two");

case 3:System.out.println("three");

}}}

optionsA)one two threeB)oneC)one twoD)Compile error.


Explanations : There is no break statement in case 1 so it causes thebelow case statements to execute regardless of their values.Questions no -44What is the output for the below code ?

public class Test {public static void main(String[] args) {

char c = 'a';

switch(c){case 65:

System.out.println("one");break;case 'a':

System.out.println("two");break;case 3:

System.out.println("three");}

}

}

optionsA)one two threeB)one


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C)twoD)Compile error - char can't be in switch statement.


Explanations : Compile properly and print two.


import java.util.NavigableMap;import java.util.concurrent.ConcurrentSkipListMap;


NavigableMap navMap = newConcurrentSkipListMap();

navMap.put(4, "April");navMap.put(5, "May");navMap.put(6, "June");navMap.put(1, "January");navMap.put(2, "February");navMap.put(3, "March");

navMap.pollFirstEntry();navMap.pollLastEntry();navMap.pollFirstEntry();System.out.println(navMap.size());

}}

optionsA)Compile error : No method name like pollFirstEntry() orpollLastEntry()B)3C)6

D)4


Explanations :

pollFirstEntry() Removes and returns a key-value mappingassociated with the least key in this map, or null if the map isempty.


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pollLastEntry() Removes and returns a key-value mapping associatedwith the greatest key in this map, or null if the map is empty.Questions no -46What is the output for the below code ?

import java.util.NavigableMap;

import java.util.concurrent.ConcurrentSkipListMap;


NavigableMap navMap = newConcurrentSkipListMap();

System.out.print(navMap.lastEntry());

}}

optionsA)Compile error : No method name like lastEntry()B)nullC)NullPointerExceptionD)0


Explanations : lastEntry() Returns a key-value mapping associatedwith the greatest key in this map, or null if the map is empty.Questions no -47What is the output for the below code ?



NavigableMapnavMap = newConcurrentSkipListMap();

navMap.put(4, "April");navMap.put(5, "May");navMap.put(6, "June");navMap.put(1, "January");navMap.put(2, "February");


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System.out.print(navMap.ceilingKey(3));

}}

optionsA)Compile error : No method name like ceilingKey()B)nullC)NullPointerExceptionD)4


Explanations : Returns the least key greater than or equal to thegiven key, or null if there is no such key.

In the above case : 3 is not a key so return 4 (least key greaterthan or equal to the given key).Questions no -48What is the output for the below code ?



NavigableMapnavMap = newConcurrentSkipListMap();

navMap.put(4, "April");navMap.put(5, "May");navMap.put(6, "June");navMap.put(1, "January");navMap.put(2, "February");

System.out.print(navMap.floorKey(3));

}}

options


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A)Compile error : No method name like floorKey()B)nullC)NullPointerExceptionD)2


Explanations : Returns the greatest key less than or equal to thegiven key, or null if there is no such key.

In the above case : 3 is not a key so return 2 (greatest key lessthan or equal to the given key).Questions no -49What is the output for the below code ?


List lst = new ArrayList();lst.add(34);lst.add(6);lst.add(6);lst.add(6);lst.add(6);lst.add(5);

NavigableSet nvset = new TreeSet(lst);System.out.println(nvset.tailSet(6));

}}

optionsA)Compile error : No method name like tailSet()B)6 34C)5D)5 6 34


Explanations : tailSet(6) Returns elements are greater than or equal

to 6.Questions no -50What is the output for the below code ?

import java.util.ArrayList;import java.util.List;import java.util.NavigableSet;import java.util.TreeSet;


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List lst = new ArrayList();lst.add(34);lst.add(6);lst.add(6);lst.add(6);lst.add(6);

NavigableSet nvset = new TreeSet(lst);nvset.pollFirst();nvset.pollLast();

System.out.println(nvset.size());

}}

optionsA)Compile error : No method name like pollFirst() or pollLast()B)0C)3D)5


Explanations :

pollFirst() Retrieves and removes the first (lowest) element, orreturns null if this set is empty.

pollLast() Retrieves and removes the last (highest) element, orreturns null if this set is empty.


import java.util.ArrayList;import java.util.List;import java.util.NavigableSet;import java.util.TreeSet;



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List lst = new ArrayList();lst.add(34);lst.add(6);lst.add(2);lst.add(8);

lst.add(7);lst.add(10);

NavigableSet nvset = new TreeSet(lst);System.out.println(nvset.lower(6)+" "+nvset.higher(6)+

" "+ nvset.lower(2));

}}

options

A)1 2 7 10 34 nullB)2 7 nullC)2 7 34D)1 2 7 10 34


Explanations :

lower() Returns the greatest element in this set strictly lessthan the given element, or null if there is no such element.

higher() Returns the least element in this set strictly greaterthan the given element, or null if there is no such element.


import java.util.ArrayList;import java.util.Iterator;import java.util.List;import java.util.NavigableSet;import java.util.TreeSet;


List lst = new ArrayList();lst.add(34);lst.add(6);lst.add(2);lst.add(8);

lst.add(7);lst.add(10);


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NavigableSet nvset = new TreeSet(lst);System.out.println(nvset.headSet(10));

}

}

optionsA)Compile error : No method name like headSet()B)2, 6, 7, 8, 10C)2, 6, 7, 8D)34


Explanations : headSet(10) Returns the elements elements are strictly less than10.

headSet(10,false) Returns the elements elements are strictly lessthan 10.

headSet(10,true) Returns the elements elements are strictly lessthan or equal to 10.


import java.io.Console;


Console con = System.console();boolean auth = false;

if (con != null){int count = 0;

do{String uname = con.readLine(null);char[] pwd = con.readPassword("Enter %s's

password: ", uname);

con.writer().write("\n\n");} while (!auth && ++count < 3);

}


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}}

optionsA)NullPointerExceptionB)It works properlyC)Compile Error : No readPassword() method in Console class.D)null


Explanations : passing a null argument to any method in Console classwill cause a NullPointerException to be thrown.

OCPJP 6 Free Mock Exam Practice Questions

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