Trắc nghiệm Core Java pptx

Which of the following can be applied to constructors: Select a valid answer Answer: D Mark: 1.0 3.. Consider the following piece of code and select the correct statement from the follo

Trắc nghiệm Core Java

1 Which of the following statements are valid, given the following variable declarations:

boolean a; boolean b; int c; (Select a valid answer)

Answer: B Mark: 1.0

2 Which of the following can be applied to constructors: (Select a valid answer)

Answer: D Mark: 1.0

3 Which of the following retain their preferred size (width and height) when added

(individually) to the North section of a container with a BorderLayout (assume that no other components or containers are present in the North section)

(Select a valid answer)

Answer: D Mark: 1.0

4 Which of the following are legal names for variables (Select a valid answer)

Answer: C Mark: 1.0

5 Consider the following piece of code and select the correct statement from the following

String s = new String("abcdefgh"); // (1)

s.replace('d', 'q'); // (2)

System.out.println(s); // (3)

(Select the one right answer)

A The code fails to compile, reporting

an error at line 2 Strings are immutable,

and therefore a replace() method is

meaningless

B The code compiles correctly, and

displays the text "abcqefgh"

C The code compiles correctly, and

displays the text "abcdefgh"

D The code compiles, but an exception

is thrown when line 2 is executed

Answer: C Mark: 1.0

6 Which of the following keywords can be applied to the variables or methods of an

interface (Select all valid answers)

Answer: A, C Mark: 0.5

7 Consider the following piece of code and select the correct statement(s):

1 class A{

2 protected int method(){

3 }

4 }

5

6 class B extends A{

7 int method(){

8 }

9 }

(Select all valid answers)

A The code fails to compile, because

you can't override a method to be more

private than its parent

B The code fails to compile, because

method() is declared as protected, and is therefore not available to any subclass

C The code fails to compile However, it

can be made to compile correctly by

prefixing line 7 with the access qualifier

"protected"

D The code fails to compile However, it

can be made to compile correctly by prefixing line 7 with the access qualifier

"public"

Answer: A, C , D Mark: 1.0

8 Consider the following piece of code (assume the Graphics context g is defined

correctly):

g.setBackground(Color.red);

g.setForeground(Color.white);

g.drawLine(10, 10, 50, 10);

g.setForeground(Color.blue);

g.drawRect(100, 100, 50, 50);

What is displayed when this code is executed (Select a valid answer)

A A blue line from (10,10) to (50,10)

and a blue rectangle with upper left

corner at (100,100)

B A white line from (10,10) to (50,10)

and a blue square with top left corner at (100,100)

C A white line from (10,10) to (10,50)

and a blue square with lower left corner

at (100,100)

D A red line from (10, 10) to (50,10)

and a red square with upper left corner at (100,100)

Answer: B Mark: 1.0

9 Consider the following piece of code

class Test{

public static void main(String [] args){

System.out.println(args[3]);

}

}

When the following is typed at the command line, what is displayed: (Select a valid answer)

java Test Metallica Justice For All

Answer: A Mark: 1.0

10 Consider the following piece of code

1 String s = "abcd";

2 Integer x = new Integer(3);

3 String s2 = s + 4;

4 s2 = null;

5 s = null;

Following the execution of which line above, is the object referenced by s2 available for garbage collection (Select the one right answer)

is available for garbage collection

executing thread is ended

Answer: C Mark: 1.0

11 What is displayed when the following piece of code is compiled and executed:

class Test{

public static void main(String [] args){

Base b = new Subclass();

System.out.println(b.x);

System.out.println(b.method());

}

}

class Base{

int x = 2;

int method(){

return x;

}

}

class Subclass extends Base{

int x = 3;

int method(){

return x;

}

}

(Select the one right answer)

A Nothing The code fails to compile

because the object b is not created in a

valid way

B 2

3

Answer: B Mark: 1.0

12 What is displayed when the following is executed:

String s1 = "aaa";

s1.concat("bbb");

System.out.println(s1);

(Select the one right answer)

A The string "aaa" B The string "aaabbb"

E The string "bbb" D The string "bbbaaa"

Answer: A Mark: 0.5

13 What is the output of the following piece of code:

1 int x = 6;

2 double d = 7.7;

3

4 System.out.println((x > d) ? 99.9 : 9);

(Select the one right answer)

thrown at line 4

Answer: B Mark: 1.0

14 Which of the following applet tags are mandatory (select all the correct answers)

Answer: A, B, C Mark: 1.0

15 What is printed out following the execution of the code below:

1 class Test{

2 static String s;

3 public static void main(String []args){

4 int x = 4;

5 if (x < 4)

6 System.out.println("Val = " + x);

7 else

8 System.out.println(s);

9 }

10 }

(Select the one right answer)

A Nothing The code fails to compile

because the String s isn't declared

correctly

B The text "Val = null" is displayed

C The string "Val = " is displayed D The text "null" is displayed

Answer: D Mark: 1.0

16 What is displayed when the following piece of code is executed (assume the graphics

context, g, is correctly set up):

g.drawString("abc", 10, 10);

(Select the one right answer)

A The text "abc" with the lower left part

of "a" located at x = 10, y = 10

B The text "abc" with the upper left part

of "a" located at x = 10, y = 10

C Nothing This is not a valid method D The text "abc" with the lower right

part of "a" located at x = 10, y = 10

Answer: A Mark: 0.5

17 To reference a JAR from a web page, which of the following keywords are used:

(Select the one right answer)

Answer: D Mark: 0.5

18 Analyse the following 2 classes and select the correct statements

class A{

private int x = 0;

static int y = 1;

protected int q = 2;

}

class B extends A{

void method(){

System.out.println(x);

System.out.println(y);

System.out.println(q);

}

}

(Select all valid answers)

A The code fails to compile because the

variable x is not available to class B

B The code compiles correctly, and the

following is displayed: 0 1 2

C The compiler will complain that the

variable x in class B is undefined

D Removing the line

"System.out.println(x)" will allow the code to compile correctly

Answer: A, C, D Mark: 1.0

19 Which of the following interfaces can be used to manage a collection of elements, with

no duplication

(Select the one right answer)

Answer: C Mark: 0.5

20 Which of the following are valid ways to define an abstract method

(Select all valid answers)

A abstract void Test();

B abstract void Test() {}

C static abstract void Test();

D final abstract void Test();

E Methods cannot be defined as abstract, only variables can be abstract

A abstract void Test(); B Methods cannot be defined as abstract,

only variables can be abstract

C abstract static void Test(); D final abstract void Test();

Answer: A Mark: 0.5