Exercise: Language Fundamentals

Questions for: Language Fundamentals

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

> java X a b

A:
names
B:
null
C:
Compilation fails
D:
An exception is thrown at runtime
Answer: B
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.
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In the given program, how many lines of output will be produced? 
public class Test 
{
    public static void main(String [] args) 
    {
    int [] [] [] x = new int [3] [] [];
    int i, j;
    x[0] = new int[4][];
    x[1] = new int[2][];
    x[2] = new int[5][];
    for (i = 0; i < x.length; i++)
    {
        for (j = 0; j < x[i].length; j++) 
        {
            x[i][j] = new int [i + j + 1];
            System.out.println("size = " + x[i][j].length);
        }
    }
    }
}
A:
7
B:
9
C:
11
D:
13
Answer: C

The loops use the array sizes (length).

It produces 11 lines of output as given below.

D:\Java>javac Test.java

D:\Java>java Test
size = 1
size = 2
size = 3
size = 4
size = 2
size = 3
size = 3
size = 4
size = 5
size = 6
size = 7

Therefore, 11 is the answer.

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What will be the output of the program? 
public class CommandArgsTwo 
{
    public static void main(String [] argh) 
    {
        int x;
        x = argh.length;
        for (int y = 1; y <= x; y++) 
        {
            System.out.print(" " + argh[y]);
        }
    }
}

and the command-line invocation is

> java CommandArgsTwo 1 2 3

A:
0 1 2
B:
1 2 3
C:
0 0 0
D:
An exception is thrown at runtime
Answer: D

An exception is thrown because at some point in (System.out.print(" " + argh[y]);), the value of x will be equal to y, resulting in an attempt to access an index out of bounds for the array. Remember that you can access only as far as length - 1, so loop logical tests should use x < someArray.length as opposed to x < = someArray.length.

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What will be the output of the program ? 
public class Test 
{
    public static void main(String [] args) 
    {
        signed int x = 10;
        for (int y=0; y<5; y++, x--)
            System.out.print(x + ", ");
    }
}
A:
10, 9, 8, 7, 6,
B:
9, 8, 7, 6, 5,
C:
Compilation fails.
D:
An exception is thrown at runtime.
Answer: C

The word "signed" is not a valid modifier keyword in the Java language. All number primitives in Java are signed. Hence the Compilation will fails.

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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
Answer: D

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.

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