代码中的“？”是什么[重复]

Question

有人能解释这些代码吗？为什么它有＜code＞在那里？

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;
}
}

Answer 1

<代码>？：是if-then-else行为的运算符

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

这意味着

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

Answer 2

这是一个三元运算符。

这一行:

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

同这个：

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

它通常用于简单的条件和分配...一行。

Answer 3

其条件/三元运算符。

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

有效与 ：

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

else
{
output = "we may never know"
}