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Count Negative Elements in an Array in Java

beginner· Arrays · Array

Problem

A negative number is any value strictly less than zero.

Given an array of integers, count how many of its elements are negative.

Input

[5, -3, 8, -1, 0, 12, -7]

Output

Negative elements: 3

Java Program

Java

public class CountNegative {
    public static void main(String[] args) {
        int[] arr = {5, -3, 8, -1, 0, 12, -7};
        int count = 0;
        for (int num : arr) {
            if (num < 0) count++; // strictly less than zero
        }
        System.out.println("Negative elements: " + count);
    }
}

▶ Run Code

Output

Negative elements: 3

Core Logic

A single pass through the array, checking each number against zero, tallies every negative value — the mirror image of counting positives.

How It Works

1A for-each loop visits each element of the array in turn.
2num < 0 checks whether the current number is strictly less than zero.
3A match increments the count variable; anything else is skipped.
4After the loop, count holds the total number of negative elements.

For [5, -3, 8, -1, 0, 12, -7], the scan finds -3, -1, and -7 — three negative elements.

💡

Key Point: Zero is excluded from both the positive and negative counts — num < 0 correctly treats it as neither, keeping the two counts from overlapping.

Complexity

Time Complexity: O(n)Space Complexity: O(1)

Why: Each element is visited once, and only a single running counter is kept regardless of array size.

Key Concepts

comparison operatorfor-each loopcounter variable

Approach 2: Java 8

Java

import java.util.Arrays;

public class CountNegativeStream {
    public static void main(String[] args) {
        int[] arr = {5, -3, 8, -1, 0, 12, -7};
        // filter() keeps only values strictly less than zero
        long count = Arrays.stream(arr).filter(num -> num < 0).count();
        System.out.println("Negative elements: " + count);
    }
}

▶ Run Code

Output

Negative elements: 3

Core Logic

The same comparison can filter a stream of the array's values down to just the negative ones, then count what's left.

How It Works

1Arrays.stream(arr) converts the int[] into an IntStream.
2.filter(num -> num < 0) keeps only the values strictly less than zero.
3.count() reduces the filtered stream down to a single long total.

Filtering [5, -3, 8, -1, 0, 12, -7] keeps -3, -1, -7, so count() returns 3.

💡

Key Point: Flipping > 0 to < 0 is the only change needed to turn the positive-counting stream into this one — the rest of the pipeline stays identical.

Complexity

Time Complexity: O(n)Space Complexity: O(1)

Why: The stream still visits every element once, and count() reduces straight down to a single long without collecting anything.

Key Concepts

StreamIntStreamfilter()count()

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