whats the '?' in code

Question

can someone explain these code? why does it have ? in there?

package course.examples.theanswer;

import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;

public class TheAnswer extends Activity {

public static final int[] answers = { 42, -10, 0, 100, 1000 };
public static final int answer = 42;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.answer_layout);

    TextView answerView = (TextView) findViewById(R.id.answer_view);


    int val = findAnswer();
    String output = (val == answer) ? "42" : "We may never know";
    answerView.setText("The answer to life, the universe and everything is:\n\n"
                    + output);
}

private int findAnswer() {
    for (int val : answers) {
        if (val == answer)
            return val;
    }
    return -1;
}
}

http://en.wikipedia.org/wiki/%3F: - damn, there's a bug in SO link creation in comments... — Denys Séguret, Jul 30 '14 at 08:49
Ternary operator. It means `if(val == answer) { output = "42"; } else { output = "We may never know"; }`. — EpicPandaForce, Jul 30 '14 at 08:50
It's the conditional operator: http://docs.oracle.com/javase/specs/jls/se8/html/jls-15.html#jls-15.25 — Jon Skeet, Jul 30 '14 at 08:50
thanks for the answers guys, and sorry I couldnt find the '?' question before — user37933gg, Jul 31 '14 at 07:22

TheLostMind · Accepted Answer · 2014-07-30T09:10:32.330

7

Its conditional / ternary operator.

String output = (val == answer) ? "42" : "We may never know";

effectively same as :

if(val==answer)
{
 output = "42" 
}

else
{
output = "we may never know"
}

edited Jul 30 '14 at 09:10

answered Jul 30 '14 at 08:50

TheLostMind

35,966
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1

Force OP to use curly braces. – Suresh Atta Jul 30 '14 at 08:53
@sᴜʀᴇsʜᴀᴛᴛᴀ - yes.. You are right.. :) – TheLostMind Jul 30 '14 at 08:58

Ninad Pingale · Answer 2 · 2014-07-30T08:57:39.177

1

This is called a Ternary operator. It's a kind of Replacement for if-else statement.

(Condition) ? {if true execute this} : {else do this}

edited Jul 30 '14 at 08:57

answered Jul 30 '14 at 08:50

Ninad Pingale

6,801
5
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*{if true execute this} : {else do this}* It does not just execute, it ***assigns*** – BackSlash Jul 30 '14 at 08:58

score 1 · Answer 3 · answered Jul 30 '14 at 08:50

It's a ternary operator..

this line:

String output = (val == answer) ? "42" : "We may never know";

is the same as this:

String output;
if (val == answer) {
  output = "42";
} else {
  output = "We may never know";
}

It is usually used for simple conditions and assignments...a one-liner.

score 1 · Answer 4 · answered Jul 30 '14 at 08:51

1

?: is operator for if-then-else behavior

(val == answer) ? "42" : "We may never know";

this means

if(val==answer) {
    output = "42"
} else { 
     output = "We may never know";
}

answered Jul 30 '14 at 08:51

Sanjeev

9,876
2
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score 1 · Answer 5 · answered Jul 30 '14 at 08:51

If you mean this line:

String output = (val == answer) ? "42" : "We may never know";
    answerView.setText("The answer to life, the universe and everything is:\n\n"
                    + output);

This ? is a short form of (if...then...else).

if (val == answer) then output = "42" else output = "We may never know"; answerView.setText("The answer to life, the universe and everything is:\n\n" + output)

score 1 · Answer 6 · answered Jul 30 '14 at 08:51

On this line

String output = (val == answer) ? "42" : "We may never know";

the ? represents the ternary operator: http://docs.oracle.com/javase/tutorial/java/nutsandbolts/op2.html

if val == answer is true, the value assigned to output will be "42". If it equates to false, it will be assigned "We may never know"

val = answer;
...
String output = (val == answer) ? "42" : "We may never know";
System.out.println(output);

would output:

42

whereas:

val = answer + 1;
...
String output = (val == answer) ? "42" : "We may never know";
System.out.println(output);

would output:

We may never know

whats the '?' in code

6 Answers6