import java.math.BigInteger;
import java.nio.charset.StandardCharsets;
/**
Base‑36 encoding/decoding in Java
-------------------------------------------
Base‑36 digits: 0–9, A–Z
Encoding:
- Convert string → bytes → BigInteger (base‑256)
- Convert BigInteger → base‑36 using toString(36)
Decoding:
- Convert base‑36 → BigInteger
- Convert BigInteger → bytes → original string
Java's BigInteger already supports:
- Arbitrary‑precision arithmetic
- Base conversion via toString(radix)
- Parsing via new BigInteger(String, radix)
This makes the implementation clean and efficient.
*/
public class Base36Codec {
// Encode any string into Base‑36
public static String encodeToBase36(String input) {
/**
Convert string → bytes (UTF‑8)
Then interpret bytes as a positive BigInteger.
*/
byte[] bytes = input.getBytes(StandardCharsets.UTF_8);
BigInteger big = new BigInteger(1, bytes); // 1 = positive number
/**
Convert BigInteger → Base‑36 string
BigInteger.toString(36) uses digits 0‑9 + a‑z.
We convert to uppercase to match your specification.
*/
return big.toString(36).toUpperCase();
}
// Decode Base‑36 back into the original string
public static String decodeFromBase36(String encoded) {
/**
Convert Base‑36 text → BigInteger
*/
BigInteger big = new BigInteger(encoded, 36);
/**
Convert BigInteger → bytes → original UTF‑8 string
*/
byte[] bytes = big.toByteArray();
/**
BigInteger.toByteArray() may include a leading zero byte
if the number's highest bit is set.
We remove it if present.
*/
if (bytes.length > 1 && bytes[0] == 0) {
byte[] trimmed = new byte[bytes.length - 1];
System.arraycopy(bytes, 1, trimmed, 0, trimmed.length);
bytes = trimmed;
}
return new String(bytes, StandardCharsets.UTF_8);
}
// Usage
public static void main(String[] args) {
String text = "Hello Universe!";
String encoded = encodeToBase36(text);
String decoded = decodeFromBase36(encoded);
System.out.println("Original: " + text);
System.out.println("Base-36 encoded: " + encoded);
System.out.println("Decoded: " + decoded);
}
}
/*
run:
Original: Hello Universe!
Base-36 encoded: LP4N024HJ1YVBVD84Y8TYQP
Decoded: Hello Universe!
*/
