字符串数组随机化 ArrayIndexOutOfBoundsException（已编辑）

Question

需要帮助的家伙。我在代码中添加了随机方法，现在出现此错误。

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12-17 11:03:38.921: E/AndroidRuntime(306): FATAL EXCEPTION: main
12-17 11:03:38.921: E/AndroidRuntime(306): java.lang.ArrayIndexOutOfBoundsException
12-17 11:03:38.921: E/AndroidRuntime(306):  at com.example.boardrace.MainActivity.isCorrect(MainActivity.java:97)
12-17 11:03:38.921: E/AndroidRuntime(306):  at com.example.boardrace.MainActivity.checkAnswer(MainActivity.java:107)
12-17 11:03:38.921: E/AndroidRuntime(306):  at com.example.boardrace.MainActivity$1.onClick(MainActivity.java:48)
12-17 11:03:38.921: E/AndroidRuntime(306):  at android.view.View.performClick(View.java:2408)
12-17 11:03:38.921: E/AndroidRuntime(306):  at android.view.View$PerformClick.run(View.java:8816)
12-17 11:03:38.921: E/AndroidRuntime(306):  at android.os.Handler.handleCallback(Handler.java:587)
12-17 11:03:38.921: E/AndroidRuntime(306):  at android.os.Handler.dispatchMessage(Handler.java:92)
12-17 11:03:38.921: E/AndroidRuntime(306):  at android.os.Looper.loop(Looper.java:123)
12-17 11:03:38.921: E/AndroidRuntime(306):  at android.app.ActivityThread.main(ActivityThread.java:4627)
12-17 11:03:38.921: E/AndroidRuntime(306):  at java.lang.reflect.Method.invokeNative(Native Method)
12-17 11:03:38.921: E/AndroidRuntime(306):  at java.lang.reflect.Method.invoke(Method.java:521)
12-17 11:03:38.921: E/AndroidRuntime(306):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
12-17 11:03:38.921: E/AndroidRuntime(306):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
12-17 11:03:38.921: E/AndroidRuntime(306):  at dalvik.system.NativeStart.main(Native Method)

这是我在 youtube 上看到的全部代码

public class MainActivity extends Activity {

private int currentQuestion;
private String [] questions;
private String [] answers;
private Button answerButton;
private Button questionButton;
private TextView questionView;
private TextView answerView;
private EditText answerText; 

Random random = new Random();
String randString = questions[random.nextInt(questions.length)];

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    init();
}

public void init()
{questions = new String[]{"Q1?","Q2","Q3","Q4","Q5","Q6","Q7","Q8","Q9","Q10"};
 answers = new String[]{"A1","A2","A3","A4","A5","A6","A7","A8","A9","10",};
 currentQuestion = -1;
 answerButton = (Button)findViewById(R.id.AnswerButton);
 questionButton = (Button)findViewById(R.id.QuestionButton);
 questionView = (TextView) findViewById(R.id.QuestionTextView);
 answerView = (TextView) findViewById(R.id.AnswerTextView);
 answerText = (EditText) findViewById(R.id.AnswerText);

 answerButton.setOnClickListener(new OnClickListener(){
 @Override
 public void onClick(View v) {checkAnswer();              }});

 questionButton.setOnClickListener(new OnClickListener(){
     @Override
 public void onClick(View v) {
 showQuestion();
     }});
}

public void showQuestion()
{ currentQuestion++;
 if(currentQuestion == questions.length)
 currentQuestion =0;
questionView.setText(questions[currentQuestion]);
 answerView.setText("");
 answerText.setText("");
}

public boolean isCorrect(String answer)
{return (answer.equalsIgnoreCase(answers[currentQuestion]));
}

public void checkAnswer()
{String answer = answerText.getText().toString();
 if(isCorrect(answer))
 answerView.setText("You're right!");
 else answerView.setText("Sorry, the correct answer is "+answers[currentQuestion]);
}
}

代码是关于问题的随机化，您将输入正确的答案。

Answer 1

String randString = questions[random.nextInt(questions.length)];

由于randString被声明为成员变量，所以在创建类的对象时给this赋值，这个赋值依赖于questions，在init()中初始化，这个init()会被调用对象创建后。这就是你得到ArrayIndexOutOfBoundException 的原因，因为你在初始化之前尝试访问questions。

流程：

1. 对象已创建。

2. 成员被初始化。

   2.a) randString 被赋值，但这需要question。

   2.b) 所以现在，question 已被查找。

   2.c) 只能找到question 的声明。 question 不是指任何值。

   2.d) 现在 questions[random.nextInt(questions.length)] 正在尝试访问某个索引 (random int) 处的值，但 question 直到现在还没有任何东西。

   This is point where exception is raised.

Solution

如果randString 是一些初始化参数，那么做

init(){
// some code
questions = new String[]{"Q1?","Q2","Q3","Q4","Q5","Q6","Q7","Q8","Q9","Q10"};
String randString = questions[random.nextInt(questions.length)];
// some code
} 

Answer 2

试试这个：

questions[random.nextInt(questions.length-1)];

这个想法是数组位置从 0 开始。所以你的问题数组的值在 0 到 9 之间。

你传递的总长度是 10，它超出了最后一个位置，即 9。

Answer 3

尝试删除答案数组末尾的逗号“，”

answers = new String[]{"A1","A2","A3","A4","A5","A6","A7","A8","A9","10",};

作为

answers = new String[]{"A1","A2","A3","A4","A5","A6","A7","A8","A9","10"};

Answer 4

问题是你初始化了currentQuestion = -1;。所以如果第一次点击回答按钮没有点击前面的问题按钮，它将执行：

public boolean isCorrect(String answer) {
     return (answer.equalsIgnoreCase(answers[-1]));
}

因此IndexOutOfBoundsException。