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📦 Variables & Types · Beginner

char and Unicode in Java

char is a 16-bit UTF-16 code unit; char arithmetic and code points.

🧩 The mysteryWhat's 'x' + 'y'? Not "xy". And why does Java say the text "😀" has length 2? Time to open up the char.

A char is a number in disguise

A char is a 16-bit UTF-16 code unit: a number from 0 to 65,535 that stands for a character. Because it's a number, you can do arithmetic with it.

int a = 'A';      // 65
int lower = 'a';  // 97
int zero = '0';   // 48, not 0!
int space = ' ';  // 32
🔮 Predict it

Your turn

What does this print?

System.out.println('x' + 'y');
  1. xy
  2. 241
  3. Compile error
Show the answer

Both chars are promoted to int: 120 + 121 = 241. + only joins text when one operand is a String: "" + 'x' + 'y' gives "xy".

++ keeps it a char

c + 1 produces an int. But c++ and c += 1 keep the variable a char: they include a hidden cast back to the variable's type, so the char moves to the next character.

char c = 'a';
c++;
System.out.println(c);  // b

When 16 bits aren't enough

Unicode has over a million possible code points (characters). Those above 65,535, like many emoji, don't fit in one char. UTF-16 stores them as two chars, called a surrogate pair. 😀 is code point U+1F600.

🔮 Predict it

Your turn

Two letters and one emoji. What does length() say?

String s = "Hi😀";
System.out.println(s.length());
  1. 3
  2. 4
  3. 6
Show the answer

4. H and i are one char each, but 😀 is a surrogate pair: two chars.

⚠️ The trap

length() counts chars, not characters

length() counts chars (UTF-16 code units). To count real characters, use codePointCount or codePoints().

String s = "😀";
s.length()                       // 2
s.codePointCount(0, s.length())  // 1
💼 In the real world

In real projects

Emoji break naive text code constantly. Cutting a message to 100 chars with substring can split a surrogate pair in half and show a broken symbol. Chat apps and username checks count code points instead.

Key takeaways

  1. 'A' is 65, 'a' is 97, '0' is 48
  2. char + int → int; char++ stays a char
  3. Emoji can take 2 chars: length() counts chars, not characters
  4. codePointCount / codePoints() count real characters
🤯 Did you know?

Java's char is 16 bits because, when Java was designed, all of Unicode fit in 16 bits. Unicode 2.0 (1996) grew beyond that, and Java 5 added code point methods to cope.

Practice questions

What does this print?

char c = 'a';
c++;
System.out.println(c);
  1. 98
  2. b
  3. a1
  4. Compile error
Check your answer

b. ++ on a char variable keeps the type char, moving to the next code unit, 'b'. Increment operators include an implicit cast back to the variable's type.

What does this print?

System.out.println('a' + 'b');
  1. ab
  2. 195
  3. a b
  4. Compile error
Check your answer

195. Both chars are promoted to int (97 + 98), so the result is 195. You need a String operand to get concatenation.

Next: the simplest type of all, boolean. Only two values... so how does if (done = true) still sneak bugs in?