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Java Program to Check Whether a Number is Positive or Negative

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A number is positive if it is greater than zero (number > 0), for example 1, 2.5 or 300. It is negative if it is less than zero (number < 0), for example -1 or -42.7. Zero is neither positive nor negative, so a correct program needs three branches, not two.

1. Positive, Negative or Zero Using if-else-if

An if-else-if chain checks the conditions one after another and runs only the first branch that matches.

PositiveNegative.java 
public class PositiveNegative {
    public static void main(String[] args) {
        int[] numbers = {50, -20, 0};

        for (int number : numbers) {
            if (number > 0) {
                System.out.println(number + " is a positive number.");
            } else if (number < 0) {
                System.out.println(number + " is a negative number.");
            } else {
                System.out.println(number + " is zero, neither positive nor negative.");
            }
        }
    }
}
Output
50 is a positive number.
-20 is a negative number.
0 is zero, neither positive nor negative.

2. Positive or Negative with User Input

This version reads a double, so it also works for decimal numbers such as -286.76.

PositiveNegativeInput.java 
import java.util.Scanner;

public class PositiveNegativeInput {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter a number: ");
        double number = scanner.nextDouble();
        scanner.close();

        if (number > 0) {
            System.out.println(number + " is a positive number.");
        } else if (number < 0) {
            System.out.println(number + " is a negative number.");
        } else {
            System.out.println("The number is zero.");
        }
    }
}
Output 1
Enter a number: 51
51.0 is a positive number.
Output 2
Enter a number: -286.76
-286.76 is a negative number.

3. Positive or Negative Using Integer.signum()

Integer.signum(n) returns 1 for positive numbers, -1 for negative numbers and 0 for zero. A switch on that value covers all three cases.

PositiveNegativeSignum.java 
public class PositiveNegativeSignum {
    public static void main(String[] args) {
        int[] numbers = {7, -3, 0};

        for (int number : numbers) {
            String result = switch (Integer.signum(number)) {
                case 1 -> "positive";
                case -1 -> "negative";
                default -> "zero";
            };
            System.out.println(number + " is " + result);
        }
    }
}
Output
7 is positive
-3 is negative
0 is zero

4. Summary

  • A number is positive if number > 0 and negative if number < 0.
  • Zero is neither, so handle it in its own branch.
  • Read a double to accept decimal numbers as well as whole numbers.
  • Integer.signum() and Math.signum() return the sign of a number as 1, -1 or 0.

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