**This book is now obsolete** Please use CSAwesome instead.

# 16.10. ArrayTester - Part A¶

The following is a free response question from 2018. It was question 4 on the exam. You can see all the free response questions from past exams at https://apstudent.collegeboard.org/apcourse/ap-computer-science-a/exam-practice.

**Question 4.** This question involves reasoning about arrays of integers. You will write two static methods, both of which are in a class named `ArrayTester`

.

```
public class ArrayTester
{
/** Returns an array containing the elements of column c of arr2D in the same order as
* they appear in arr2D.
* Precondition: c is a valid column index in arr2D.
* Postcondition: arr2D is unchanged.
*/
public static int[] getColumn(int[][] arr2D, int c)
{ /* to be implemented in part (a) */ }
/** Returns true if and only if every value in arr1 appears in arr2.
* Precondition: arr1 and arr2 have the same length.
* Postcondition: arr1 and arr2 are unchanged.
*/
public static boolean hasAllValues(int [] arr1, int [] arr2)
{ /* implementation not shown */ }
/** Returns true if arr contains any duplicate values;
* false otherwise.
*/
public static boolean containsDuplicates(int [] arr)
{ /* implementation not shown) */ }
/** Returns true if square is a Latin square as described in part (b);
* false otherwise.
* Precondition: square has an equal number of rows and columns.
* Precondition: square has at least one row.
*/
public static boolean isLatin(int[][] square)
{ /* to be implemented in part (b) */ }
}
```

**Part a.** Write a static method `getColumn`

, which returns a one-dimensional array containing the elements of a
single column in a two-dimensional array. The elements in the returned array should be in the same order as
they appear in the given column. The notation `arr2D [r][c]`

represents the array at row `r`

and
column `c`

.

The following code segment initializes an array and calls the `getColumn`

method.

`int [] [] arr2D = { { 0, 1, 2 }, { 3, 4, 5 }, { 6, 7, 8 }, { 9, 5, 3 } };`

`int[] result = ArrayTester.getColumn (arr2D, 1);`

When the code segment has completed execution, the variable result `result`

will have the following contents.
`result: {1, 4, 7, 5}`