Java Language Fundamental - Quiz

Q: Which is a reserved word in the Java programming language? native

A. method
B. native
C. subclasses
D. reference

Correct Option: B
Explanation:

The word "native" is a valid keyword, used to modify a method declaration.

Option A, D and E are not keywords. Option C is wrong because the keyword for subclassing in Java is extends, not 'subclasses'.

Q: Which is a valid declarations of a String?

A. String s1 = null;
B. String s2 = 'null';
C. String s3 = (String) 'abc';
D. String s4 = (String) '\ufeed';

Correct Option: A
Explanation:

Option A sets the String reference to null.

Option B is wrong because null cannot be in single quotes.

Option C is wrong because there are multiple characters between the single quotes ('abc').

Option D is wrong because you can't cast a char (primitive) to a String (object).

Q: Which is a valid keyword in java?

A. interface
B. string
C. Float
D. unsigned

Correct Option: A
Explanation:

interface is a valid keyword.

Option B is wrong because although "String" is a class type in Java, "string" is not a keyword.

Option C is wrong because "Float" is a class type. The keyword for the Java primitive is float.

Option D is wrong because "unsigned" is a keyword in C/C++ but not in Java.

Q: Which three are legal array declarations?

int [] myScores [];

char [] myChars;

int [6] myScores;

Dog myDogs [];

Dog myDogs [7];

A. 1, 2, 4
B. 2, 4, 5
C. 2, 3, 4
D. All are correct.

Correct Option: A
Explanation:

(1), (2), and (4) are legal array declarations. With an array declaration, you can place the brackets to the right or left of the identifier. Option A looks strange, but it's perfectly legal to split the brackets in a multidimensional array, and place them on both sides of the identifier. Although coding this way would only annoy your fellow programmers, for the exam, you need to know it's legal.

(3) and (5) are wrong because you can't declare an array with a size. The size is only needed when the array is actually instantiated (and the JVM needs to know how much space to allocate for the array, based on the type of array and the size).

Q:

public interface Foo 
{ 
    int k = 4; /* Line 3 */
}

Which three piece of codes are equivalent to line 3?

final int k = 4;
public int k = 4;
static int k = 4;
abstract int k = 4;
volatile int k = 4;
protected int k = 4;

A. 1, 2 and 3
B. 2, 3 and 4
C. 3, 4 and 5
D. 4, 5 and 6

Correct Option: A
Explanation:

(1), (2) and (3) are correct. Interfaces can have constants, which are always implicitly public, static, and final. Interface constant declarations of public, static, and final are optional in any combination.

Q: Which is the valid declarations within an interface definition?

A. public double methoda();
B. public final double methoda();
C. static void methoda(double d1);
D. protected void methoda(double d1);

Correct Option: A
Explanation:

Option A is correct. A public access modifier is acceptable. The method prototypes in an interface are all abstract by virtue of their declaration, and should not be declared abstract.

Option B is wrong. The final modifier means that this method cannot be constructed in a subclass. A finalmethod cannot be abstract.

Option C is wrong. static is concerned with the class and not an instance.

Option D is wrong. protected is not permitted when declaring a method of an interface. See information below.

Member declarations in an interface disallow the use of some declaration modifiers; you cannot use transient, volatile, or synchronized in a member declaration in an interface. Also, you may not use the private and protected specifiers when declaring members of an interface.

Q: What will be the output of the program?

public class CommandArgsThree 
{
    public static void main(String [] args) 
    {
        String [][] argCopy = new String[2][2];
        int x;
        argCopy[0] = args;
        x = argCopy[0].length;
        for (int y = 0; y < x; y++) 
        {
            System.out.print(" " + argCopy[0][y]);
        }
    }
}

What will be the output of the program? public class CommandArgsThree { publ

A. 0 0
B. 1 2
C. 0 0 0
D. 1 2 3

Correct Option: D
Explanation:

In argCopy[0] = args;, the reference variable argCopy[0], which was referring to an array with two elements, is reassigned to an array (args) with three elements.

Q: Which will legally declare, construct, and initialize an array?

A. int [] myList = {"1", "2", "3"};
B. int [] myList = (5, 8, 2);
C. int myList [] [] = {4,9,7,0};
D. int myList [] = {4, 3, 7};

Correct Option: D
Explanation:

The only legal array declaration and assignment statement is Option D

Option A is wrong because it initializes an int array with String literals.

Option B is wrong because it use something other than curly braces for the initialization.

Option C is wrong because it provides initial values for only one dimension, although the declared array is a two-dimensional array.

Q: What will be the output of the program?

 
public class X 
{
    public static void main(String [] args) 
    {
        String names [] = new String[5];
        for (int x=0; x < args.length; x++)
            names[x] = args[x];
        System.out.println(names[2]);
    }
}

and the command line invocation is

A. names
B. null
C. Compilation fails
D. An exception is thrown at runtime

Correct Option: B
Explanation:

The names array is initialized with five null elements. Then elements 0 and 1 are assigned the String values "a" and "b" respectively (the command-line arguments passed to main). Elements of names array 2, 3, and 4 remain unassigned, so they have a value of null.

Q: What will be the output of the program?

public class TestDogs 
{
    public static void main(String [] args) 
    {
        Dog [][] theDogs = new Dog[3][];
        System.out.println(theDogs[2][0].toString());
    }
}
class Dog { }

A. null
B. theDogs
C. Compilation fails
D. An exception is thrown at runtime

Correct Option: D
Explanation:

The second dimension of the array referenced by theDogs has not been initialized. Attempting to access an uninitialized object element (System.out.println(theDogs[2][0].toString());) raises a NullPointerException.

Java Language Fundamental - Quiz

Which is a reserved word in the Java programming language? native

Which is a valid declarations of a String?

Which is a valid keyword in java?

Which three are legal array declarations?

int [] myScores [];

char [] myChars;

int [6] myScores;

Dog myDogs [];

Dog myDogs [7];

public interface Foo { int k = 4; /* Line 3 */ }
Which three piece of codes are equivalent to line 3?

final int k = 4;

public int k = 4;

static int k = 4;

abstract int k = 4;

volatile int k = 4;

protected int k = 4;

Which is the valid declarations within an interface definition?

Which will legally declare, construct, and initialize an array?

What will be the output of the program?

and the command line invocation is

What will be the output of the program?
public class TestDogs { public static void main(String [] args) { Dog [][] theDogs = new Dog[3][]; System.out.println(theDogs[2][0].toString()); } } class Dog { }

Java Language Fundamental - Quiz

Which is a reserved word in the Java programming language? native

Which is a valid declarations of a String?

Which is a valid keyword in java?

Which three are legal array declarations? int [] myScores []; char [] myChars; int [6] myScores; Dog myDogs []; Dog myDogs [7];

public interface Foo { int k = 4; /* Line 3 */ } Which three piece of codes are equivalent to line 3? final int k = 4; public int k = 4; static int k = 4; abstract int k = 4; volatile int k = 4; protected int k = 4;

Which is the valid declarations within an interface definition?

Which will legally declare, construct, and initialize an array?

What will be the output of the program? public class X { public static void main(String [] args) { String names [] = new String[5]; for (int x=0; x < args.length; x++) names[x] = args[x]; System.out.println(names[2]); } } and the command line invocation is

What will be the output of the program? public class TestDogs { public static void main(String [] args) { Dog [][] theDogs = new Dog[3][]; System.out.println(theDogs[2][0].toString()); } } class Dog { }

Which three are legal array declarations?

int [] myScores [];

char [] myChars;

int [6] myScores;

Dog myDogs [];

Dog myDogs [7];

public interface Foo { int k = 4; /* Line 3 */ }
Which three piece of codes are equivalent to line 3?

final int k = 4;

public int k = 4;

static int k = 4;

abstract int k = 4;

volatile int k = 4;

protected int k = 4;

What will be the output of the program?

and the command line invocation is

What will be the output of the program?
public class TestDogs { public static void main(String [] args) { Dog [][] theDogs = new Dog[3][]; System.out.println(theDogs[2][0].toString()); } } class Dog { }