Java Program to Check Positive, Negative or Zero

Use a simple if-else statement in Java to check if a number is positive, negative, or zero like this: if (num > 0) System.out.println("Positive"); else if (num < 0) System.out.println("Negative"); else System.out.println("Zero");.

Examples

Input10

OutputPositive

Input-5

OutputNegative

Input0

OutputZero

How to Think About It

To decide if a number is positive, negative, or zero, first compare it with zero using greater than and less than checks. If it's greater than zero, it's positive; if less, it's negative; otherwise, it must be zero.

Algorithm

1

Get the input number.

2

Check if the number is greater than zero.

3

If yes, print 'Positive'.

4

Otherwise, check if the number is less than zero.

5

If yes, print 'Negative'.

6

If neither, print 'Zero'.

Code

java

public class CheckNumber {
    public static void main(String[] args) {
        int num = 10; // Change this value to test
        if (num > 0) {
            System.out.println("Positive");
        } else if (num < 0) {
            System.out.println("Negative");
        } else {
            System.out.println("Zero");
        }
    }
}

Output

Positive

Dry Run

Let's trace the input 10 through the code

1

Initialize number

num = 10

2

Check if num > 0

10 > 0 is true

3

Print result

Print 'Positive'

Step	Condition	Result
Check if num > 0	10 > 0	true
Check if num < 0	Skipped	N/A
Print output	Positive	Printed

Why This Works

Step 1: Compare number with zero

The program uses if (num > 0) to check if the number is positive.

Step 2: Check for negative

If the first check fails, else if (num < 0) checks if the number is negative.

Step 3: Handle zero

If neither condition is true, the number must be zero, so it prints Zero.

Alternative Approaches

Using ternary operator

java

public class CheckNumber {
    public static void main(String[] args) {
        int num = -3;
        String result = (num > 0) ? "Positive" : (num < 0) ? "Negative" : "Zero";
        System.out.println(result);
    }
}

This approach is shorter but can be harder to read for beginners.

Using switch expression (Java 14+)

java

public class CheckNumber {
    public static void main(String[] args) {
        int num = 0;
        String result = switch (Integer.signum(num)) {
            case 1 -> "Positive";
            case -1 -> "Negative";
            default -> "Zero";
        };
        System.out.println(result);
    }
}

Uses Java 14+ switch expressions and <code>Integer.signum()</code> for a modern style.

Complexity: O(1) time, O(1) space

Time Complexity

The program performs a fixed number of comparisons regardless of input size, so it runs in constant time O(1).

Space Complexity

It uses a fixed amount of memory for variables and no extra data structures, so space complexity is O(1).

Which Approach is Fastest?

All approaches run in constant time and space; the difference is mainly readability and style.

Approach	Time	Space	Best For
If-else statements	O(1)	O(1)	Clear and beginner-friendly
Ternary operator	O(1)	O(1)	Shorter code, less readable for beginners
Switch expression	O(1)	O(1)	Modern Java style, requires Java 14+