AP Computer Science A : Console Output

Study concepts, example questions & explanations for AP Computer Science A

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Example Questions

Example Question #31 : Programming Constructs

Which of the following blocks of code will output an evenly-spaced 2D array (i.e. an evenly-spaced matrix)?  For example, a simple evenly-spaced matrix is:

1  2  3

4  5  6

7  8  9

Possible Answers:

int[][] matrix = {{134,135,12},{31,1,41},{-14441,14,51},{14,5,134}};

for(int i = 0; i < matrix.length; i++) {

     for(int j = 0; j < matrix[i].length; j++) {

          if(j == 0) {

               System.out.print("\t\t");

          }

          System.out.print(matrix[i][j]);

     }

     System.out.println();

}

int[][] matrix = {{134,135,12},{31,1,41},{-1441,14,51},{14,5,134}};

for(int i = 0; i < matrix.length; i++) {

     for(int j = 0; j < matrix[i].length; j++) {

          System.out.print(matrix[i][j]);

     }

     System.out.print(" ");

}

int[][] matrix = {{134,135,12},{31,1,41},{-14441,14,51},{14,5,134}};

for(int i = 0; i < matrix.length; i++) {

     for(int j = 0; j < matrix[i].length; j++) {

          if(j != 0) {

               System.out.print(" ");

          }

          System.out.println(matrix[i][j]);

     }

     System.out.println();

}

int[][] matrix = {{134,135,12},{31,1,41},{-14441,14,51},{14,5,134}};

for(int i = 0; i < matrix.length; i++) {

     for(int j = 0; j < matrix[i].length; j++) {

          if(j != 0) {

               System.out.print("\t\t");

          }

          System.out.print(matrix[i][j]);

     }

     System.out.println();

}

int[][] matrix = {{134,135,12},{31,1,41},{-14441,14,51},{14,5,134}};

for(int i = 0; i < matrix.length; i++) {

     for(int j = 0; j < matrix[i].length; j++) {

          if(j != 0) {

               System.out.print(" ");

          }

          System.out.print(matrix[i][j]);

     }

     System.out.println();

}

Correct answer:

int[][] matrix = {{134,135,12},{31,1,41},{-14441,14,51},{14,5,134}};

for(int i = 0; i < matrix.length; i++) {

     for(int j = 0; j < matrix[i].length; j++) {

          if(j != 0) {

               System.out.print("\t\t");

          }

          System.out.print(matrix[i][j]);

     }

     System.out.println();

}

Explanation:

There are several critical points to look at in the code given as possible answers above.  

First, you need to make sure that the main output is not a new line.  Thus, the following is incorrect:

System.out.println(matrix[i][j]);

This would create a new line for every single value!

Next, you need to make sure that a new line is output after every row of the matrix.  This is the final output statement.   Thus, it cannot be:

System.out.print(" ");

This would only output a character with no new line.

Finally, for everything except for the first element of each row, you will need to output sufficient padding before the given element element (so as to make the matrix to be evenly-spaced).  We are not going to be too particular here about the problem of very big numbers—the values are given to us as is.  Note that it is insufficient to use a mere space for this.  You should use a tab character (defined as '\t').  A space will not guarantee enough spacing (no pun intended)!

The correct answer has the following logic:

 if(j != 0) {

      System.out.print("\t\t");

 }

This means "when the column is not the first column" (i.e. j != 0), "then output tabs to space sufficiently."

Example Question #32 : Programming Constructs

Consider the following code:

for(int i = 1; i <= 10; i++) {

     for(int j = 0; j < (20 - i * 2) / 2; j++) {

          System.out.print(" ");

     }

     for(int j = 0; j < i * 2; j++) {

          System.out.print("*");

     }

     for(int j = 0; j < (20 - i * 2) / 2; j++) {

          System.out.print(" ");

     }

     System.out.println();

}

Describe the output of the code above.

Possible Answers:

An arrow pointing downward, having a base 20 characters wide and a top that is 2 characters wide.

An arrow pointing upward, having a base 20 characters wide and a top that is 2 characters wide.

An arrow pointing upward, having a base 20 characters wide and a top that is 1 character wide.

A left-facing arrow with a large base of 20 characters in size and a point that is 1 character wide.

A right-facing arrow with large base of 20 characters in size and a point that is 2 characters wide.

Correct answer:

An arrow pointing upward, having a base 20 characters wide and a top that is 2 characters wide.

Explanation:

This code is best explained by analyzing it directly.  Comments will be provided in bold below:

// The loop runs from 1 to 10

for(int i = 1; i <= 10; i++) {

     // First, you run through 0 to some number

     // That number is computed by taking the current value of i, doubling it,

     //   subtracting that from 20, then dividing by 2.  

     // So, consider the following values for i:

     // 0: 20 - 0 = 20; Divided by 2: 10

     // 1: 20 - 2 = 18; Divided by 2: 9

     // 2: 20 - 2 = 16; Divided by 2: 8

     //    etc...

     // Thus, you will output single spaces that number of times (10, 9, 8...)

     for(int j = 0; j < (20 - i * 2) / 2; j++) {

          System.out.print(" ");

     }

     // Next, you will output an asterix i * 2 number of times.  Thus, your

     // smallest value is 2 and your largest 20.

     for(int j = 0; j < i * 2; j++) {

          System.out.print("*");

     }

     // This is just a repeat of the same loop from above

     for(int j = 0; j < (20 - i * 2) / 2; j++) {

          System.out.print(" ");

     }

     // This bumps us down to the next line

     System.out.println();

}

Thus, you have output that basically has even padding on the left and right, with an increasing number of asterix characters (2, 4, 6, etc).  This is an upward-facing arrow, having a point of width 2 and a base of width 20.

Example Question #33 : Programming Constructs

Consider the following code:


Q3

What is the output of the method call mystery("Green eggs and ham")

Possible Answers:

Green eggs and ham,

Green,eggs,and,ham,

Greeneggsandham,

,G,r,e,e,n, ,e,g,g,s, ,a,n,d, ,h,a,m,

ham,

Correct answer:

,G,r,e,e,n, ,e,g,g,s, ,a,n,d, ,h,a,m,

Explanation:

The method String.split() splits a String into an array of Strings separated according to the expression within the method argument. The expression String.split("") splits the String at every character. The "for" loop concatenates the elements of the String array together, separated by a comma. 

Example Question #34 : Programming Constructs

public static void main(String[] args) {

       int[][] x = {{4,5,6,7},{91,15,14,13}};

       int[][] y = {{-13,4,41,14},{14,5,13,3}};

       int[][] z = doWork(x,y);

       for(int i = 0; i < z.length; i++) {

              for(int j = 0; j < z[0].length;j++) {

                     System.out.print(z[i][j] + " ");

              }

              System.out.println();

       }

}

 

public static int[][] doWork(int[][] a, int[][] b) {

       int[][] ret = new int[a.length][a[0].length];

       for(int i = 0; i < a.length; i++) {

              for(int j = 0; j < a[i].length; j++) {

                     ret[i][j] = a[i][j] + b[i][j];

              }

       }

       return ret;

}

What is the console output for the code above?

Possible Answers:

22 133

46 35

68

168

236

-9 9 47 21 

105 20 27 16 

4 4 6 7

14 5 13 3

Correct answer:

-9 9 47 21 

105 20 27 16 

Explanation:

The doWork method implements a relatively standard type of 2D array iteration, one that goes through each element. The outer loop goes through the first dimension of the array. Then, the inner loop provides index for the second dimension. From this, you get the total 2D index [i][j]. The line ret[i][j] = a[i][j] + b[i][j]; actually performs the operation at the given index. Here, it performs an addition, combining the values at [i][j] found in the two arrays. This gives you the sum at each index of ret. The main method outputs each of these values, following the same standard algorithm for 2D array traversal.

Example Question #34 : Programming Constructs

int a = 10, b = 5;

for(int i = 0; i < a; i+=2) {

    for(int j = 0; j < i % b; j++) {

        System.out.print("* ");

    }

    System.out.println();

}

What will be the console output for the code above?

Possible Answers:

 

* * 

* * * * 

* * * 

*

* *

* * *

* * * * 

* * * * * 

* * * *

* * *

* * 

 

 

* * *

* *

*

* *

* * *

* * * 

* * * 

* *

* * 

* *

* * *

*

*

* *

Correct answer:

 

* * 

* * * * 

* * * 

Explanation:

All this problem requires is careful attention to the loop control variables.  Notice that the first loop adds 2 to i every looping.  This means that it will run for 0,2,4,6, and 8.  Thus, a total of five lines will be printed.

Now, the second loop dictates the number of * characters that will be output per line.  This is going to be based upon the result of the modulus i % b.  Remember, modulus is a remainder calculation.  Thus, you will have:

0 % 5 = 0

2 % 5 = 2

4 % 5 = 4

6 % 5 = 1

8 % 5 = 3

Hence, you will have the following (note the first line is empty, given the result of 0 % 5): 


* * 

* * * * 

* * * 

Example Question #38 : Programming Constructs

LOGIC WITH 2-D ARRAYS

Given:

int[][] myArray = { {1, 2},

                                 {3, 4} }; 

 

What would the following statement print out to the console?

     

System.out.print(myArray[1][1] + 10);

Possible Answers:

12

13

11

14

Correct answer:

14

Explanation:

Before anything is printed out into the console, the following is first evaluated:

myArray[1][1] + 10

 

myArray[1][1] is referring to the item that is in row=1 and column=1 of myArray. Taking note that arrays start with row 0 and column 0, we see that the item in row 1 column 1 is the number 4. Now we have the following: 4+10. This evaluates to 14. Therefore, the Java print statement will print out the number 14 on the console.

Example Question #41 : Program Implementation

What is the output of this program?

 

arr = ["hello", "my", "name", "is"]

for (int i = 0; i < arr.length - 1; i++) {

    System.out.println(arr[i]);

}

System.out.println("Sandra");

Possible Answers:

Sandra

hello my name is Sandra

hello my name is

hello

my

name

is

Sandra

Correct answer:

hello

my

name

is

Sandra

Explanation:

The words are printed on separate lines due to the System.out.println() call and then whatever is inside of the parentheses is printed on the next line. This call is different from System.out.print() which prints words on the same lines.

Therefore, the Sysytem.out.printIn gives("Sandra"):

hello

my

name

is

Sandra

Example Question #2 : Console Output

True or False.

The output of this code snippet will be "Hello, I'm hungry!"

 

public static void meHungry() {

String hungry = "hungry";

String iAm = "I'm";

String hello = "Hello";

String message = "";

if (hungry != null) {

message += hungry;

}

if (hello != null && iAm != null) {

message = hello + iAm + hungry;

}

System.out.println(message);

}

Possible Answers:

True

False

Correct answer:

False

Explanation:

The message that is printed out is "Hello I'm hungry"

Notice there is no punctuation in the message. The code does not add punctuation to the message, but prints the words out in the same order as the phrase in the prompt. Be mindful of what's actually happening in the code. 

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