What does the "?" key do in Java?

Question

I've been trying to Google it, but googling the key "?" doesn't really work out that good. I really want to know what it does and when to use it.

Thanks!

I've seen it a couple times, but here is an example of one I just saw

String name = perms.calculateRank().getColor() + player.getName();
//This is a custom ranking system ^
player.setPlayerListName(name.length() > 15 ? name.substring(0, 16) : name);
player.setDisplayName(name + ChatColor.RESET);
Chat.sendMessage(player, "Tab Name Set");

Posting the code that uses the symbol would help identify its meaning. — M A, Oct 23 '14 at 19:17
I googled for "question mark operator java"---and guess what I found. — Marko Topolnik, Oct 23 '14 at 19:23
@MarkoTopolnik OK, but if you're suggesting that the questioner should have just found their answer with Google--nothing in their question indicated that they knew it was called an "operator", and there are probably plenty of people out there who don't know that `?` is a "question mark". — ajb, Oct 23 '14 at 19:30
@ajb If that's true, then I managed to teach OP three new things with four words :) — Marko Topolnik, Oct 23 '14 at 19:50

Justin Johnson · Answer 1 · 2014-10-23T19:52:05.040

8

This is a ternary operator. In Java specifically, it is called the Conditional Operator. It is a way of writing short-hand simple if..else statements. For example:

if (a == b) {
   c = 123;
} else {
   c = 456;
}

is the same as:

c = a == b ? 123 : 456;

edited Oct 23 '14 at 19:52

answered Oct 23 '14 at 19:19

Justin Johnson

30,978
7
65
89

score 7 · Answer 2 · answered Oct 23 '14 at 19:20

7

It is also used for a wildcard generic.

public List<?> getBizarreList();

answered Oct 23 '14 at 19:20

Jazzwave06

1,883
1
11
19

score 1 · Answer 3 · answered Oct 23 '14 at 19:21

1

The ternary operator someBoolean ? x : y evaluates to x if someBoolean is true, and y otherwise.

answered Oct 23 '14 at 19:21

mattm

5,851
11
47
77

Kick Buttowski · Answer 4 · 2014-10-23T19:28:18.503

It is called ternary operator and it is only operator that takes 3 operands. In better sense, it is conditional operator that represent shorter format

General Syntax :

boolean expression ? value1 : value2

your example:

 player.setPlayerListName(name.length() > 15 ? name.substring(0, 16) : name);

as same as

  if( name.length() > 15)
    player.setPlayerListName(name.substring(0, 16));
  else
    player.setPlayerListName(name);

What does the "?" key do in Java?

4 Answers4