Language Fundamentals - Finding the output Questions and Answers

Q: What will be the output of the program? and the command-line invocation is 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]); } } } > java CommandArgsThree 1 2 3

Correct answer: 1 2 3Assigning args to argCopy[0] replaces the two-element array that was there with a reference to the command line array itself - array references are assigned, not copied element by element, and the declared inner length of 2 is not a constraint on what may later be stored there. So x becomes 3 and the loop prints all three arguments. The new String[2][2] is a red herring, and the array it created for row 0 is simply discarded.

Q: What will be the output of the program? public class CommandArgs { public static void main(String [] args) { String s1 = args[1]; String s2 = args[2]; String s3 = args[3]; String s4 = args[4]; System.out.print(" args[2] = " + s2); } } and the command-line invocation is > java CommandArgs 1 2 3 4

Correct answer: An exception is thrown at runtime.Four arguments give args indices 0 to 3, so args[4] is out of bounds and throws ArrayIndexOutOfBoundsException. The throw happens on the fourth assignment, before any output is produced, so nothing is printed at all - not even the value of args[2], which had been read successfully a moment earlier.

Q: 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 + ", "); } } }

Correct answer: Compilation fails.Java has no signed keyword. Its integral types are signed by definition - there is no unsigned counterpart to declare against - so the word is not part of the language and signed int x = 10; is rejected. It is a C and C++ construct, and the same applies to unsigned. Nothing runs, so neither of the printed sequences arises.

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 > java X a 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.

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 { }

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.

Q: 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

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.

What will be the output of the program?

and the command-line invocation is

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]);
        }
    }
}

> java CommandArgsThree 1 2 3

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

Answer: D

Correct answer: 1 2 3

Assigning args to argCopy[0] replaces the two-element array that was there with a reference to the command line array itself - array references are assigned, not copied element by element, and the declared inner length of 2 is not a constraint on what may later be stored there. So x becomes 3 and the loop prints all three arguments. The new String[2][2] is a red herring, and the array it created for row 0 is simply discarded.

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What will be the output of the program?

public class CommandArgs 
{
    public static void main(String [] args) 
    {
        String s1 = args[1];
        String s2 = args[2];
        String s3 = args[3];
        String s4 = args[4];
        System.out.print(" args[2] = " + s2);
    }
}

and the command-line invocation is

> java CommandArgs 1 2 3 4

A.args[2] = 2
B.args[2] = 3
C.args[2] = null
D.An exception is thrown at runtime.

Answer: D

Correct answer: An exception is thrown at runtime.

Four arguments give args indices 0 to 3, so args[4] is out of bounds and throws ArrayIndexOutOfBoundsException. The throw happens on the fourth assignment, before any output is produced, so nothing is printed at all - not even the value of args[2], which had been read successfully a moment earlier.

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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

Correct answer: Compilation fails.

Java has no signed keyword. Its integral types are signed by definition - there is no unsigned counterpart to declare against - so the word is not part of the language and signed int x = 10; is rejected. It is a C and C++ construct, and the same applies to unsigned. Nothing runs, so neither of the printed sequences arises.

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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
E.Compilation fails

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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public class F0091 
{    
    public void main( String[] args ) 
    {  
        System.out.println( "Hello" + args[0] ); 
    } 
}

What will be the output of the program, if this code is executed with the command line:

> java F0091 world

A.Hello
B.Hello Foo91
C.Hello world
D.The code does not run.

Answer: D

Option D is correct. A runtime error will occur owning to the main method of the code fragment not being declared static:

Exception in thread "main" java.lang.NoSuchMethodError: main

The Java Language Specification clearly states: "The main method must be declared public, static, and void. It must accept a single argument that is an array of strings."

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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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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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