Java How to Convert Hexadecimal to Decimal Number

Use Integer.parseInt(hexString, 16) in Java to convert a hexadecimal string to a decimal integer.

Examples

Input"1A"

Output26

Input"FF"

Output255

Input"0"

Output0

How to Think About It

To convert hexadecimal to decimal, think of the hex string as a base-16 number. Each digit represents a value from 0 to 15. Java's Integer.parseInt method can convert this string by specifying base 16, which automatically calculates the decimal value.

Algorithm

1

Get the hexadecimal string input.

2

Use a built-in method to parse the string as a base-16 number.

3

Return or print the resulting decimal integer.

Code

java

public class HexToDecimal {
    public static void main(String[] args) {
        String hex = "1A";
        int decimal = Integer.parseInt(hex, 16);
        System.out.println(decimal);
    }
}

Output

26

Dry Run

Let's trace converting "1A" to decimal using Integer.parseInt with radix 16.

1

Input Hex String

hex = "1A"

2

Parse Hex String

Integer.parseInt("1A", 16) converts '1A' to decimal 26

3

Output Decimal

decimal = 26

Hex Digit	Decimal Value
1	1 * 16 = 16
A	10 * 1 = 10

Why This Works

Step 1: Parsing with radix 16

The Integer.parseInt method takes the string and the base (16 for hex) to convert each digit correctly.

Step 2: Hex digits to decimal values

Each hex digit is converted to its decimal equivalent (0-15), then multiplied by powers of 16 based on position.

Step 3: Summing values

The method sums these values to produce the final decimal integer.

Alternative Approaches

Using Integer.valueOf

java

public class HexToDecimalAlt {
    public static void main(String[] args) {
        String hex = "FF";
        int decimal = Integer.valueOf(hex, 16);
        System.out.println(decimal);
    }
}

Works similarly to parseInt but returns an Integer object instead of primitive int.

Manual conversion with loop

java

public class HexToDecimalManual {
    public static void main(String[] args) {
        String hex = "1A";
        int decimal = 0;
        for (int i = 0; i < hex.length(); i++) {
            char c = hex.charAt(i);
            int value = Character.digit(c, 16);
            decimal = decimal * 16 + value;
        }
        System.out.println(decimal);
    }
}

Manually converts each digit; useful for learning but less concise.

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

Time Complexity

Parsing processes each character once, so time grows linearly with string length.

Space Complexity

Uses constant extra space for variables; no additional data structures needed.

Which Approach is Fastest?

Using built-in Integer.parseInt is fastest and simplest; manual loops are slower and more error-prone.

Approach	Time	Space	Best For
Integer.parseInt(hex, 16)	O(n)	O(1)	Simple and fast conversion
Integer.valueOf(hex, 16)	O(n)	O(1)	When Integer object needed
Manual loop with Character.digit	O(n)	O(1)	Learning or custom parsing