Ôn thi tốt nghiệp: java + uml ( in oop (using java) subject ) Question 1

What is the output of running A?

public class A extends B {

int x = 1;

public static void main(String[] args) {

System.out.print(new A().x);

System.out.print(new B().x);

}

}

int x = 5;

}

1. 
   51
   
2. 
   11
   
3. 
   55
   
4. 
   15
   

What is the output of running class C?

class A {

public A() {

System.out.println(

"The default constructor of A is invoked");

}

}

class B extends A {

System.out.println(

"The default constructor of B is invoked");

}

}

public static void main(String[] args) {

B b = new B();

}

}

"The default constructor of B is invoked"

"The default constructor of B is invoked"

b) none

"The default constructor of B is invoked"

"The default constructor of A is invoked"

Question 253–d

What is the output of running class Test.

public class Test {

public static void main(String[] args) {

new Circle9();

}

}

protected GeometricObject() {

System.out.print("A");

}

protected GeometricObject(String color, boolean filled) {

}

}

/** Default constructor */

public Circle9() {

this(1.0);

System.out.print("C");

}

/** Construct circle with a specified radius */

this(radius, "white", false);

System.out.print("D");

}

/** Construct a circle with specified radius, filled, and color */

super(color, filled);

System.out.print("E");

}

}

1. 
   AEDC
   
2. 
   CBAE
   
3. 
   ABCD
   
4. 
   BEDC
   
5. 
   BACD
   

What is the output of the following code?

1 int i = 45678;

2 int j = ~i;

3

4 System.out.println(j);

1. 
   Compilation error at line 2. ~ operator applicable to boolean values only
   
2. 
   Prints 45677
   
3. 
   Prints –45679
   
4. 
   Prints -45677
   

What is the output of the following code?

class X {

public static void main (String x [ ]) {

B myB = new B( );

if (myB instanceof C)

System.out.println ("TRUE");

else

}//main

1. 
   FALSE
   
2. 
   TRUE FALSE
   
3. 
   doesn't compile
   
4. 
   no output to screen
   
5. 
   TRUE
   

What is the output of the following code?

int m;

for (int j = 2, m = 1; j > 0; j--) {

if (k == 1) break;

System.out.println (j+" "+m+" "+k);

}

}

1. 
   212, 211, 112, 111
   
2. 
   211, 112, 111
   
3. 
   none of the other answers (or code doesn't compile)
   
4. 
   212, 211, 210, 112, 111, 110
   
5. 
   212, 112
   

What is the output of the following code:

public class Test {

public static void main(String[] args) {

Object o1 = new Object();

Object o2 = new Object();

System.out.print((o1 == o2) + " " + (o1.equals(o2)));

}

}

1. 
   true true
   
2. 
   true false
   
3. 
   false true
   
4. 
   false false
   

What is the output of the following code:

public class Test {

public static void main(String[] args) {

String s1 = new String("Java");

String s2 = new String("Java");

System.out.print((s1 == s2) + " " + (s1.equals(s2)));

}

}

1. 
   false true
   
2. 
   true true
   
3. 
   false false
   
4. 
   true false
   

What is the output of the following code?

public class Test {

public static void main(String[] args) {

String s1 = new String("Welcome to Java");

String s2 = s1;

s1 += "and Welcome to HTML";

if (s1 == s2)

System.out.println("s1 and s2 reference to the same String object");

else

}

}

1. 
   s1 and s2 reference to different String objects
   
2. 
   s1 and s2 reference to the same String object
   

What is the output of the following code?

public class Test {

public static void main(String[] args) {

String s1 = new String("Welcome to Java!");

String s2 = s1.toUpperCase();

if (s1 == s2)

System.out.println("s1 and s2 reference to the same String object");

else if (s1.equals(s2))

System.out.println("s1 and s2 have the same contents");

else

System.out.println("s1 and s2 have different contents");

}

1. 
   s1 and s2 have different contents
   
2. 
   s1 and s2 reference to the same String object B. s1 and s2 have the same contents
   

What is the output of the following code segment?

int num = 4;

int power = 3;

int product = 0;

int i = 0;

for (i = 0; i < power; i++)

product *= num;

System.out.println(product);

1. 
   64
   
2. 
   16
   
3. 
   256
   
4. 
   0
   

What is the output of the following code snippet?

public static void main (String x[ ]) {

int a = 4;

a ^= 2;

System.out.println (a);

1. 
   The code prints out 6
   
2. 
   The code doesn't compile because there is no shortcut expression ^=
   
3. 
   The code prints out 0
   
4. 
   The code doesn't compile because you cannot print a variable that has been ^'d
   
5. 
   The code prints out 4
   

What is the output of the following program?

33. import java.util.*;

34. class Question {

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

36. HashSet set = new HashSet();

37. String s1 = "abc";

38. String s2 = "def";

39. String s3 = "";

40. set.add(s1);

41. set.add(s2);

42. set.add(s1);

43. set.add(s2);

44. Iterator i = set.iterator();

45. while(i.hasNext()){

46. s3 += (String) i.next();

47. }

48. System.out.println(s3);

}

1. 
   defabc
   
2. 
   fedcbafedcba
   
3. 
   abcdefabcdef
   
4. 
   defabcdefabc
   

What is the output of the following program?

import java.util.*;

public class Question {

public static void main(String args[]){

String strings[] = {"skis","bobsled",

"figure skates"};

List list = Arrays.asList(strings);

displayList(list);

}

static void displayList(List list) {

while(i.hasNext()){

Object o = i.next();

if(o == null) System.out.println("null");

else System.out.println(o.toString());

}

}

a) bobsled

figure skates

skis

bobsled

c) null

What is the output of the following program?

public class Test {

public static void main(String[] args) {

new A();

}

{

}

}

A() {

}

{

}

}

B() {

}

{

}

}

1. 
   YBXA
   
2. 
   BXAY
   
3. 
   XYAB
   
4. 
   YBXAZ
   

What is the output of the following program?

public class Test extends Object {

public static void main(String[] args) {

Test test = new Test();

}

public Test() {

}

{

}

static {

}

}

1. 
   BAC
   
2. 
   ABC
   
3. 
   ACB
   
4. 
   CBA
   
5. 
   CAB
   

What is the output of the following program when it is invoked using the command line java Test: what do you say?

class Test {

public static void main(String[] args) {

System.out.println(args[2]);

}

}

1. 
   what
   
2. 
   say
   
3. 
   you
   
4. 
   do
   

What is the path from node C to I?

1. 
   C, H, G, I
   
2. 
   C, G, E, I
   
3. 
   C, B, H, I
   
4. 
   C, E, H, I
   
5. 
   C, D,E, I
   

What is the printout for the first statement in the main method?

public class Foo {

static int i = 0;

static int j = 0;

public static void main(String[] args) {

int i = 2;

int k = 3;

{

int j = 3;

}

k = i + j;

System.out.println("j is " + j);

}

}

1. 
   i + j is 22
   
2. 
   i + j is 23
   
3. 
   i + j is 6
   
4. 
   i + j is 5
   

What is the printout of the second println statement in the main method?

public class Foo {

int i;

public static void main(String[] args) {

Foo f1 = new Foo();

System.out.println("f1.i is " + f1.i + " f1.s is " + f1.s);

Foo f2 = new Foo();

System.out.println("f2.i is " + f2.i + " f2.s is " + f2.s);

Foo f3 = new Foo();

System.out.println("f3.i is " + f3.i + " f3.s is " + f3.s);

}

public Foo() {

s++;

}

1. 
   f2.i is 1 f2.s is 2
   
2. 
   f2.i is 2 f2.s is 1
   
3. 
   f2.i is 2 f2.s is 2
   
4. 
   f2.i is 1 f2.s is 1
   

What is the printout for the third statement in the main method?

public class Foo {

static int i = 0;

static int j = 0;

public static void main(String[] args) {

int i = 2;

int k = 3;

{

int j = 3;

}

k = i + j;

System.out.println("j is " + j);

}

}

1. 
   j is 1
   
2. 
   j is 3
   
3. 
   j is 2
   
4. 
   j is 0
   

What is the purpose of count < phrase.length in the following code?

int[] letterCount = new int[26];

for (int count = 0; count < phrase.length; count++) {

String current = phrase[count];

char[] letters = current.toCharArray();

}

1. 
   sets the count variable to the number of letters in a phrase
   
2. 
   determines the number of letters in a phrase
   
3. 
   makes the loop stop when the end of the phrase array is reached
   

What is the purpose of the getSeconds() method in this class?

public class Virus {

private int newSeconds = 86;

public int getSeconds() {

return newSeconds;

}

1. 
   it changes the value of newSeconds
   
2. 
   there is not enough code to tell what its purpose is
   
3. 
   it makes the value newSeconds available to other objects
   

What is the result of compiling and running the following program.

Select the one correct answer.

class test {

public static void main(String args[]) {

char ch;

String test = new String("abcd");

if(test.equals(test2)) {

if(test == test2)

ch = test.charAt(0);

else

}

else {

ch = test.charAt(2);

else

ch = test.charAt(3);

System.out.println(ch);

}

}

1. 
   'c'
   
2. 
   'b'
   
3. 
   'a'
   
4. 
   'd'
   

What is the result of executing the following Java class:

import java.awt.*;

public class FrameTest extends Frame {

public FrameTest() {

add (new Button("First"));

add (new Button("Second"));

add (new Button("Third"));

pack();

setVisible(true);

}

public static void main(String args []) {

}

}

1. 
   Nothing happens.
   
2. 
   A runtime exception is generated (no layout manager specified).
   
3. 
   Three buttons are displayed across a window.
   
4. 
   Only the "second" button is displayed.
   
5. 
   Only the "third" button is displayed.
   
6. 
   Only the "first" button is displayed.
   

What is the result of the following code?

class X {

int myVar;

X ( ) {

System.out.println (myVar);

}//--------------------------------------

class Driver {

public static void main(String x[]) {

X myX= new X();

}

}//---------------------------------------

1. 
   the code compiles but will the give a Runtime Exception
   
2. 
   the code compiles and prints out 0
   
3. 
   The code doesn't compile because the attribute myVar was never initialized
   
4. 
   The code doesn't compile because print statements aren't allowed in the constructor
   

What is the results of the code below?

byte b = 6;

byte c = 201;

System.out.println ("B + C =" + (b+c));

1. 
   The code does not compile
   
2. 
   The code prints out "B + C =-41"
   
3. 
   The code prints out "B + C =207"
   

What is the result of the following program?

class Question {

public static void main(String[] args) {

int i = 7;

int j = 8;

int n = (i | j) % (i j);

System.out.print(n);

}

}

1. 
   15
   
2. 
   0
   
3. 
   An ArithmeticException is thrown.
   
4. 
   -15
   

What is the value displayed by the following program?

class Question {

public static void main(String[] args) {

int x=0;

boolean b1, b2, b3, b4;

b1=b2=b3=b4=true;

x=(b1 | b2 b3 ^ b4) ? x++ : --x;

System.out.println(x);

}

}

1. 
   2
   
2. 
   0
   
3. 
   –1
   
4. 
   –2
   
5. 
   3
   
6. 
   1
   

What is the value of data after execution of the following code?

JTextField [] data = new JTextField[10];

for(int i=0; i

data[i] = new JTextField(20);

}

1. 
   data = null
   
2. 
   data[i] = null
   
3. 
   data[i] stores a reference to an array object
   
4. 
   data[i] stores a reference to a JTextField
   

What is the value of myCount.count displayed?

public class Test {

public static void main(String[] args) {

Count myCount = new Count();

int times = 0;

for (int i=0; i<100; i++)

increment(myCount, times);

System.out.println(

"myCount.count = " + myCount.count);

System.out.println("times = "+ times);

}

public static void increment(Count c, int times) {

times++;

}

class Count {

Count(int c) {

count = c;

}

Count() {

}

}

1. 
   98
   
2. 
   101
   
3. 
   100
   
4. 
   99
   

What is the value of data after execution of the following code?

JTextField [] data = new JTextField[10];

for(int i=0; i

data[i] = new JTextField(20);

}

1. 
   data[i] stores a reference to an array object
   
2. 
   data[i] = null
   
3. 
   data = null
   
4. 
   data[i] stores a reference to a JTextField
   

What is the value of the variable age when it is displayed in the following method?

public static void main(String args[])

{

int age=30;

System.out.println("Age is "+age+". Cost is "+cost);

}

1. 
   45.0
   
2. 
   30.0
   
3. 
   30
   
4. 
   45
   

What is the value of times displayed?

public class Test {

public static void main(String[] args) {

Count myCount = new Count();

int times = 0;

for (int i=0; i<100; i++)

increment(myCount, times);

System.out.println(

"myCount.count = " + myCount.count);

System.out.println("times = "+ times);

}

public static void increment(Count c, int times) {

times++;

}

class Count {

Count(int c) {

count = c;

}

Count() {

}

}

1. 
   100
   
2. 
   101
   
3. 
   98
   
4. 
   0
   

What is the value of y after execution of the following statements?

int x = 5;

int y = 4;

y = x++;

1. 
   5
   
2. 
   6
   
3. 
   7
   
4. 
   4
   

What is written to the standard output as the result of executing the following statements?

Boolean bl = new Boolean(true);

Boolean b2 = new Boolean(true);

Object obj 1 = (Obj ect) b1;

Object obj2 = (Object) b2;

if(objl ==obj2)

if (obj 1.equals(obj2))

System.out.println("a");

else

else

System.out.println("c");

else

System.out.println("d");

1. 
   b
   
2. 
   a
   
3. 
   d
   
4. 
   c
   

What is written to the standard output given the following statement:

System.out.println(4 7);

1. 
   4
   
2. 
   7
   
3. 
   5
   
4. 
   0
   
5. 
   6
   

What is wrong with the following code?

final class First {

private int a = 1;

intb=2;

}

class Second extends First {

System.out.println(a + b);

}

}

1. 
   You cannot invoke println() without passing it a String
   
2. 
   Second cannot extend First
   
3. 
   Since a is private, no classes other than First can access it
   
4. 
   final is not a valid keyword for a class
   

What is wrong with the following code segment?

int [] data = new int[9];

for(int i = 0; i<=9; i+=1){

data[i] = i;

}

1. 
   nothing wrong
   
2. 
   data[i] = i; should be data = i;
   
3. 
   i<=9 should be i<9
   
4. 
   int [] data = new int[9] should be int [] data;
   

What keyword can you use to refer to the methods and variables of a superclass?

1. 
   this
   
2. 
   call
   
3. 
   get
   
4. 
   super
   

What modifier should you use on a class so that a class in the same package can access it but a class in a different package cannot access it?

1. 
   Protected
   
2. 
   Private
   
3. 
   Use the default modifier.
   
4. 
   public
   

What modifier should you use on the members of a class so that they are not accessible to another class in a different package, but are accessible to any subclasses in any package?

1. 
   protected
   
2. 
   public
   
3. 
   Use the default modifie
   
4. 
   private
   

What must be true for the RuriHandler class so that instances of RunHandler can be used as written in the code below:

class Test {

public static void main(String[] args) {

Thread t = new Thread(new RunHandler());

t.start();

}

}

1. 
   RunHandler must provide a run() method declared as public and returning void.
   
2. 
   RunHandler must extend the Thread class.
   
3. 
   RunHandler must implement the java.lang.Runnable interface.
   
4. 
   RunHandler must provide an init() method.
   

What order can you place the following pieces of a source file in so that the source file will compile without errors or warnings?

//A

import j ava.applet. *;

class Helper {

}

//C

//D

}

1. 
   A, B, C, D
   
2. 
   C, A, B, D
   
3. 
   C, A, D, B
   
4. 
   A, C, B, D
   
5. 
   C, B, A, D
   

What output does the following program display?

14. import java.util.*;

15. class Question {

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

17. String s1 = "abc";

18. String s2 = "def";

19. Stack stack = new Stack();

20. stack.push(s1);

21. stack.push(s2);

22. try {

23. String s3 = (String) stack.pop() + (String) stack.pop();

24. System.out.println(s3);

25. }catch(EmptyStackException ex){

26. }

27. }

1. 
   abcabc
   
2. 
   defabc
   
3. 
   abcdef
   
4. 
   defdef