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Convert Decimal to Hexadecimal in Java

beginner· Numbers · Number Conversion

Problem

Hexadecimal is base 16; it needs sixteen digit symbols, so it uses 0 to 9 followed by A to F for the values 10 to 15.

Given a non-negative integer, print its hexadecimal representation in uppercase.

Input

3054

Output

BEE

Java Program

Java

public class DecimalToHexadecimal {
    public static void main(String[] args) {
        int number = 3054;
        String digits = "0123456789ABCDEF"; // index = digit value

        if (number == 0) {
            System.out.println("Hexadecimal of 0: 0");
            return;
        }

        StringBuilder hex = new StringBuilder();
        int n = number;
        while (n > 0) {
            hex.append(digits.charAt(n % 16)); // remainders 10 to 15 become A to F
            n /= 16;
        }

        System.out.println("Hexadecimal of " + number + ": " + hex.reverse());
    }
}

▶ Run Code

Output

Hexadecimal of 3054: BEE

Core Logic

Dividing by 16 removes the lowest hex digit each time, and a 16-character lookup string turns each remainder into its symbol.

How It Works

1digits holds "0123456789ABCDEF", so digits.charAt(r) is the symbol for remainder r.
2n % 16 gives the lowest digit's value, from 0 to 15.
3n /= 16 moves on to the next digit.
4The symbols are collected backwards and reversed at the end.

3054 → remainder 14 (E), 190 → 14 (E), 11 → 11 (B). Reversed: BEE.

💡

Key Point: The lookup string replaces an if chain for 10 to 15 — indexing into a table is a common trick for any digit-to-symbol mapping.

Complexity

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

Why: Each step divides by 16, giving one iteration and one stored character per hex digit.

Key Concepts

while looplookup stringcharAt()

Approach 2: Using Integer.toHexString() and String.format()

Java

public class DecimalToHexadecimalBuiltIn {
    public static void main(String[] args) {
        int number = 3054;
        System.out.println("toHexString: " + Integer.toHexString(number));        // lowercase digits
        System.out.println("Uppercase:   " + Integer.toHexString(number).toUpperCase());
        System.out.println("Formatted:   " + String.format("0x%04X", number));     // padded, with prefix
    }
}

▶ Run Code

Output

toHexString: bee
Uppercase:   BEE
Formatted:   0x0BEE

Core Logic

The library offers two routes: toHexString for a plain conversion, and String.format when you need padding or a prefix.

How It Works

1Integer.toHexString(3054) returns lowercase "bee".
2.toUpperCase() gives the conventional uppercase form.
3String.format("0x%04X", 3054) pads to four digits and adds the 0x prefix.

The three lines print bee, BEE and 0x0BEE.

💡

Key Point: %x prints lowercase and %X uppercase — handy for colour codes like #0BEE00 or memory addresses.

Complexity

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

Why: Each method still builds one character per hex digit.

Key Concepts

Integer.toHexString()String.format()%X specifier

Interview Questions

How do you get uppercase hex digits?

Integer.toHexString(n).toUpperCase() or String.format("%X", n).

How many hex digits does a byte need?

Two, because each hex digit represents four bits.

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