從二進制文件中讀取和打印一個隨機元素

Question

現在我有一個二進制文件，它充滿了5組問題，答案和點值。我需要從二進制文件中挑選一個隨機問題及其匹配答案和分值，並將其打印出來。我怎麼去做這件事，因爲與二進制文件，我不認爲我可以只使用nextLine()等等。任何幫助表示讚賞，謝謝！

import java.io.*; 

public class Trivia implements Serializable { 
private String question; 
private String answer; 
private int points; 

public Trivia() { 
    question = " "; 
    answer = " "; 
    points = 0; 
} 

public String getQuestion() { 
    return question; 
} 

public String getAnswer() { 
    return answer; 
} 

public int getPoints() { 
    return points; 
} 

public void setQuestion(String q) { 
    question = q; 
} 

public void setAnswer(String a) { 
    answer = a; 
} 

public void setPoints(int p) { 
    points = p; 
} 

} 
import java.io.*; 
import java.util.*; 

public class Driver { 

public static void main(String[] args) { 

    Trivia[] t = new Trivia[5]; 
    for (int i = 0; i < 5; i++) { 
     t[i] = new Trivia(); 
    } 

    t[0].setQuestion("How many states are in the US?"); 
    t[0].setAnswer("50"); 
    t[0].setPoints(1); 

    t[1].setQuestion("Who is the richest person in the US"); 
    t[1].setAnswer("You"); 
    t[1].setPoints(1); 

    t[2].setQuestion("How many senators come from each state?"); 
    t[2].setAnswer("2"); 
    t[2].setPoints(2); 

    t[3].setQuestion("What is the largest state?"); 
    t[3].setAnswer("Alaska"); 
    t[3].setPoints(2); 

    t[4].setQuestion("Who was the thrid president?"); 
    t[4].setAnswer("Thomas Jefferson"); 
    t[4].setPoints(3); 

    ObjectOutputStream outputStream = null; 

    try { 
     outputStream = new ObjectOutputStream(new FileOutputStream("trivia.dat")); 

    } catch (IOException e) { 
     System.out.println("Could not open file"); 
     System.exit(0); 
    } 

    try { 
     outputStream.writeObject(t); 
     outputStream.close(); 
    } catch (IOException e) { 
     System.out.println("Writing error"); 
     System.exit(0); 
    } 

    ObjectInputStream inputStream = null; 


    try { 
     inputStream = new ObjectInputStream(new FileInputStream("trivia.dat")); 

    } catch (IOException e) { 
     System.out.println("File not found."); 
     System.exit(0); 
    } 
    Trivia[] test = null; 

    try { 
     test = (Trivia[]) inputStream.readObject(); 
    } catch (Exception e) { 
     System.out.println("Reading error"); 
     System.exit(0); 
    } 

} 

ArrayList<Trivia> triviaQuestions = new ArrayList<Trivia>(5); 
ObjectInputStream ois = new ObjectInputStream(new FileInputStream("trivia.dat")); 
triviaQuestions.add((Trivia) ois.readObject()); // This should be repeated (looped) until all questions are read 


} 

下面是二進制文件的截圖： http://imgur.com/a/zask2

Answer 1

假設的題量沒有那麼大，我建議閱讀完整的文件，同時存儲問題的對象（包括theire答案財產和點）列表中。然後你可以從這個列表中請求一個隨機問題。

List<Question> questions = readQuestions(); 
Question randomQuestion = questions.get((new Random()).nextInt(questions.size())); 

關於二進制文件

它看起來像文件是使用用ObjectOutputStream創建更新。閱讀它可以使用ObjectInputStream類。逐一讀取每個對象將其添加到列表中。您可以使用它像這樣：

ObjectInputStream in = new ObjectInputStream(new FileInputStream("path_to_file")); 
tiviaQuestions.add((Trivia) in.readObject()); // This should be repeated (looped) until all questions are read 

你最終Driver類應該是這樣的：

public class Driver { 

public static void main(String[] args) { 

    Trivia[] t = new Trivia[5]; 
    for (int i = 0; i < 5; i++) { 
     t[i] = new Trivia(); 
    } 

    t[0].setQuestion("How many states are in the US?"); 
    t[0].setAnswer("50"); 
    t[0].setPoints(1); 

    t[1].setQuestion("Who is the richest person in the US"); 
    t[1].setAnswer("You"); 
    t[1].setPoints(1); 

    t[2].setQuestion("How many senators come from each state?"); 
    t[2].setAnswer("2"); 
    t[2].setPoints(2); 

    t[3].setQuestion("What is the largest state?"); 
    t[3].setAnswer("Alaska"); 
    t[3].setPoints(2); 

    t[4].setQuestion("Who was the thrid president?"); 
    t[4].setAnswer("Thomas Jefferson"); 
    t[4].setPoints(3); 

    ObjectOutputStream outputStream = null; 

    try { 
     outputStream = new ObjectOutputStream(new FileOutputStream("trivia.dat")); 

    } catch (IOException e) { 
     System.out.println("Could not open file"); 
     System.exit(0); 
    } 

    try { 
     outputStream.writeObject(t); 
     outputStream.close(); 
    } catch (IOException e) { 
     System.out.println("Writing error"); 
     System.exit(0); 
    } 

    ObjectInputStream inputStream = null; 
    ArrayList<Trivia> triviaQuestions = new ArrayList<Trivia>(); 

    try { 
     inputStream = new ObjectInputStream(new FileInputStream("trivia.dat")); 

     for(int i=0; i<5; i++){ // Repeats the content of the loop five times 
      triviaQuestions.add((Trivia) inputStream.readObject()); 
     } 
     inputStream.close(); // Closes the input stream because it is not longer needed 


    } catch (IOException e) { 
     System.out.println("File not found."); 
     System.exit(0); 
    } 

    Trivia yourRandomTrivia = triviaQuestions.get((new Random()).nextInt(triviaQuestions.size())); // This will be your random question 

} 

// You did not get an auto complete suggestion because you typed outside of a method 


}