Lab 14: Array Statistics

Learning Objectives

After completing this lab, you will be able to:

• Declare, initialize, and fill an array from user input
• Traverse an array to compute sum, average, maximum, and minimum
• Implement linear search returning an index or -1
• Use Arrays.toString() to print array contents for debugging

What You’re Building

A statistics calculator that reads integers into an array, then computes sum, average, max, min, and searches for a target value. Each operation is its own static method that accepts an int[] parameter. This is the standard pattern for array utility methods in Java.

Concepts and Common Misconceptions

Checkpoint 1: Fill and Print (1 pt)

Write a method fillArray(Scanner scanner, int size) that creates an int[] of the given size, prompts the user for each value, and returns the filled array.

In main, call fillArray, then print the result with Arrays.toString().

Enter 5 values:
10 20 30 40 50
Your array: [10, 20, 30, 40, 50]

Debugging tip: If you get an ArrayIndexOutOfBoundsException, your loop runs past size - 1. Array indices go from 0 to length - 1.

Checkpoint 2: sum, average, max, min (1 pt)

Write four static methods, each accepting an int[] parameter:

• sum(int[] arr) – return the sum of all elements.
• average(int[] arr) – return the average as a double.
• max(int[] arr) – return the largest element.
• min(int[] arr) – return the smallest element.

int[] data = {10, 20, 30, 40, 50};
sum(data)     // 150
average(data) // 30.0
max(data)     // 50
min(data)     // 10

Initialize max to arr[0] and min to arr[0], then loop starting at index 1.

Debugging tip: If average returns 30 instead of 30.0, you are doing integer division. Cast the sum to double before dividing: return (double) sum(arr) / arr.length;.

Checkpoint 3: linearSearch (1 pt)

Write linearSearch(int[] arr, int target) that returns the index of the first occurrence of target in arr, or -1 if not found.

int[] data = {10, 20, 30, 40, 50};
linearSearch(data, 30) // 2
linearSearch(data, 99) // -1

Loop through the array. When you find a match, return the index immediately. If the loop finishes without finding a match, return -1.

Debugging tip: If your method always returns -1, check your comparison. For int arrays, == is correct (unlike Strings). If it always returns 0, you might be returning outside the loop and hitting the default before the loop runs.

How to Debug

1. Use Arrays.toString for everything. After filling the array, print it immediately to verify the contents before running any calculations.
2. Test with known data. Hard-code int[] test = {1, 2, 3, 4, 5}; and verify that sum returns 15, average returns 3.0, max returns 5, min returns 1.
3. Test edge cases. An array with one element. An array with all identical values. An array with negative numbers.
4. Read the stack trace. ArrayIndexOutOfBoundsException tells you exactly which index was out of range. The line number points to the exact loop iteration that failed.

Scoring Breakdown