How to Check Positive or Negative Number in Java

The Challenge

Determine if a number is positive, negative, or zero!

Solution

java

public class Main {
    public static void main(String[] args) {
        int number = -5;
        
        if (number > 0) {
            System.out.println(number + " is positive");
        } else if (number < 0) {
            System.out.println(number + " is negative");
        } else {
            System.out.println("Number is zero");
        }
    }
}
// Output: -5 is negative

Using Ternary Operator

java

int number = 10;
String result = (number > 0) ? "positive" : 
                (number < 0) ? "negative" : "zero";
System.out.println(number + " is " + result);
// Output: 10 is positive

Using Method

java

public static String checkNumber(int num) {
    if (num > 0) return "positive";
    else if (num < 0) return "negative";
    else return "zero";
}

// Usage
System.out.println(checkNumber(15));  // positive
System.out.println(checkNumber(-7));  // negative
System.out.println(checkNumber(0));   // zero

Did You Know?

In Java, zero is neither positive nor negative. It's a neutral number that separates positive and negative numbers on the number line!

Pro Tip

Use Math.signum() for a concise approach:

java

double result = Math.signum(-5);
// Returns: -1.0 (negative), 0.0 (zero), or 1.0 (positive)

Real-World Use Cases

Banking: Check if account balance is positive or negative
Temperature: Determine if temperature is above or below freezing
Gaming: Check if player score is positive or negative
Data analysis: Classify numerical data

›Short versionOpen if you only have a minute.

Three outcomes need three branches: greater than zero, less than zero, and equal to zero.
An if/else that only tests > 0 labels zero as negative.
Every comparison with NaN is false, including NaN == 0.
-0.0 compares equal to 0.0. Double.compare distinguishes the two bit patterns.

Positive, negative, or zero

Classify a numeric value as positive, negative, or zero.

Working approach

Test > 0, then < 0, and leave equality as the remaining case.
For a double, reject NaN before the comparisons.
Keep the classification separate from printing.

Walk the sample

Input -8
num > 0 is false
num < 0 is true
The value is negative

The trap

Double.NaN is not positive, not negative, and not zero. A chain of comparisons falls through to whichever branch you wrote last.

java

static String sign(double value) {
    if (Double.isNaN(value)) {
        return "not a number";
    }
    if (value > 0) {
        return "positive";
    }
    if (value < 0) {
        return "negative";
    }
    return "zero";
}

Which branch does Double.NaN take in if (n > 0) else if (n < 0) else?

Neither comparison is true. NaN falls into the else and is reported as zero unless you test Double.isNaN first.

NaN == NaN is also false. Equality is not a way to detect it.

Time O(1), space O(1).

Easy to get wrong

Using one else and labeling zero as negative.
Comparing a double without a NaN check.