Java题库——Chapter17 二进制I/0

Introduction to Java Programming 的最后一章，完结撒花！
Chapter 17 Binary I/O

Section 17.2 How is I/O Handled in Java?
1. Which of the following statements are true?
a. A File object encapsulates the properties of a file or a path, but does not contain the methods for reading/writing.
b. You can use the PrintWriter class for outputting text to a file.
c. You can use the Scanner class for reading text from a file.
d. An input object is also called an input stream.
e. An output object is also called an output stream.
Key:abcde
File对象封装了文件或路径属性，但是不包含从/向文件读/写数据的方法

使用Scanner类读取文本数据，使用PrintWriter类写文本数据

输入对象从文件中读取数据流，输出对象将数据流写入文件。

输入对象也称作输入流，输出对象也称作输出流。

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Section 17.3 Text I/O vs. Binary I/O
2. Which of the following statements are true?
a. Text I/O is built upon binary I/O to provide a level of abstraction for character encoding and decoding.
b. Text I/O involves encoding and decoding.
c. Binary I/O does not require conversions.
d. Binary I/O is more efficient than text I/O, because binary I/O does not require encoding and decoding.
e. Binary files are independent of the encoding scheme on the host machine and thus are portable.
Key:abcde

文本I/O建立在二进制I/O之上，为字符编码和解码提供了一个抽象级别。
文本I/O涉及编码和解码。
二进制I/O不需要转换。
二进制I/O比文本I/O更有效，因为二进制I/O不需要编码和解码。
二进制文件与主机的编码方案无关，因此是可移植的。

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Section 17.4 Binary I/O Classes

注意这张图所描述的类之间的关系。

3.    Which method can you use to find out the number of the bytes in a file using InputStream?
a.    length()
b.    available()
c.    size()
d.    getSize()
Key:b

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4. Which of the following statements are true?
a. All methods in FileInputStream/FileOutputStream are inherited from InputStream/OutputStream.
b. You can create a FileInputStream/FileOutputStream from a File object or a file name using FileInputStream/FileOutputStream constructors.
c. The return value -1 from the read() method signifies the end of file.
d. A java.io.FileNotFoundException would occur if you attempt to create a FileInputStream with a nonexistent file.
e. A java.io.FileNotFoundException would occur if you attempt to create a FileOutputStream with a nonexistent file.
Key:abcd

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5. To append data to an existing file, use _____________ to construct a FileOutputStream for file out.dat.
a. new FileOutputStream("out.dat")
b. new FileOutputStream("out.dat", false)
c. new FileOutputStream("out.dat", true)
d. new FileOutputStream(true, "out.dat")
Key:c

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6.    What does the following code do?

FileInputStream fis = new FileInputStream("test.dat");
a.    It creates a new file named test.dat if it does not exist and opens the file so you can write to it.
b.    It creates a new file named test.dat if it does not exist and opens the file so you can write to it and read from it.
c.    It creates a new file named test.dat regardless of whether it exists or not and opens the file so you can write to it.
d.    It creates a new file named test.dat regardless of whether it exists or not and opens the file so you can write to it and read from it.
e. It creates a FileInputStream for test.dat if test.dat exists.
Key:e

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7.    Which type of exception occurs when creating a DataInputStream for a nonexistent file?
a.    FileNotExist
b.    FileNotExistException
c.    FileNotFound
d.    FileNotFoundException
Key:d

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8.    Which of the following statements is correct to create a DataOutputStream to write to a file named out.dat?
a.    DataOutputStream outfile = new DataOutputStream(new File("out.dat"));
b.    DataOutputStream outfile =  new DataOutputStream(new FileOutputStream("out.dat"));
c.    DataOutputStream outfile = new DataOutputStream(FileOutputStream("out.dat"));
d.    DataOutputStream outfile =  new DataOutputStream("out.dat");
Key:b

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9. After the following program is finished, how many bytes are written to the file t.dat?

import java.io.*;

public class Test {
  public static void main(String[] args) throws IOException {
    DataOutputStream output = new DataOutputStream(
      new FileOutputStream("t.dat"));
    output.writeShort(1234);
    output.writeShort(5678);
    output.close();
  }
}

a. 2 bytes.
b. 4 bytes.
c. 8 bytes.
d. 16 bytes.
Key:b Each short number takes 2 bytes. So total is 4 bytes.

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10. After the following program is finished, how many bytes are written to the file t.dat?

import java.io.*;

public class Test {
  public static void main(String[] args) throws IOException {
    DataOutputStream output = new DataOutputStream(
      new FileOutputStream("t.dat"));
    output.writeChar('A');
    output.close();
  }
}

a. 2 bytes.
b. 4 bytes.
c. 8 bytes.
d. none of the above.
Key:a Two bytes of Unicode for 'A' is written

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11. After the following program is finished, how many bytes are written to the file t.dat?

import java.io.*;

public class Test {
  public static void main(String[] args) throws IOException {
    DataOutputStream output = new DataOutputStream(
      new FileOutputStream("t.dat"));
    output.writeChars("ABCD");
    output.close();
  }
}

a. 2 bytes.
b. 4 bytes.
c. 8 bytes.
d. 12 bytes.
e. 16 bytes.
Key:c Two bytes of Unicode for each character is written to output.

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12. After the following program is finished, how many bytes are written to the file t.dat?

import java.io.*;

public class Test {
  public static void main(String[] args) throws IOException {
    DataOutputStream output = new DataOutputStream(
      new FileOutputStream("t.dat"));
    output.writeUTFString("ABCD");
    output.close();
  }
}

以UTF格式写一个字符串s

a. 2 bytes.
b. 4 bytes.
c. 6 bytes.
d. 8 bytes.
e. 10 bytes.
Key:c "ABCD" are ASCII code, so each takes one byte in UTF. Total is 6 because the first two bytes stores the number of characters in the string.

头两个字节存储的是字符串中的字符个数。

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13. Which of the following statements are true?
a. All files are stored in binary format. So, all files are essentially binary files.
b. Text I/O is built upon binary I/O to provide a level of abstraction for character encoding and decoding.
c. Encoding and decoding are automatically performed by text I/O.
d. For binary input, you need to know exactly how data were written in order to read them in correct type and order.
Key:abcd
所有文件都以二进制格式存储。所以，所有的文件本质上都是二进制文件。
文本I/O建立在二进制I/O之上，为字符编码和解码提供了一个抽象级别。
编码和解码由文本I/O自动执行。
对于二进制输入，需要确切地知道数据是如何写入的，以便以正确的类型和顺序读取它们。

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Section 17.6 Object I/O
14. Which of the following statements are true?
a. ObjectInputStream/ObjectOutputStream enables you to perform I/O for objects in addition for primitive type values and strings.
b. Since ObjectInputStream/ObjectOutputStream contains all the functions of DataInputStream/DataOutputStream, you can replace DataInputStream/DataOutputStream completely by ObjectInputStream/ObjectOutputStream.
c. To write an object, the object must be serializable.
d. The Serializable interface does not contain any methods. So it is a mark interface.
e. If all the elements in an array is serializable, the array is serializable too.
Key:abcde

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15. The Loan class given in the text does not implement java.io.Serializable. Analyze the following code.

public class Foo implements java.io.Serializable {
  private int v1;
  private static double v2;
  private Loan v3 = new Loan();
}

a. An instance of Foo can be serialized because Foo implements Serializable.
b. An instance of Foo cannot be serialized because Foo contains a non-serializable instance variable v3.
c. If you mark v3 as transient, an instance of Foo is serializable.
Key:bc An object may not be serialized even though its class implements java.io.Serializable, because it may contain non-serializable instance variables.

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16. Which of the following statements is not true?

a. A static variable is not serialized.
b. A transient variable is not serialized.
c. An object must be an instance of Serializable or Externalizable for it to be serialized.
d. The methods in an object are serialized.
e. All of the above are true.
Key:d
方法不能序列化
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Section 17.7 Random Access Files
17.    To create a file, you can use __________.
a.    FileOutputStream
b.    FileWriter
c.    RandomAccessFile
d.    All of the above.
Key:d

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18.    Which of the following is the legal mode for creating a new RandomAccessFile stream?
a.    "w"
b.    'r'
c.    "rw"
d.    "rwx"
Key:c

如果文件不存在则不能够使用模式"r"了，必须使用模式“rw”

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19.    What happens if the file test.dat does not exist when you attempt to compile and run the following code?

import java.io.*;

class Test  {
  public static void main(String[] args) {
    try {
      RandomAccessFile raf =
        new RandomAccessFile("test.dat", "r");
      int i = raf.readInt();
    }
    catch(IOException ex) {
      System.out.println("IO exception");
    }
  }
}

a.    The program does not compile because raf is not created correctly.
b.    The program does not compile because readInt() is not implemented in RandomAccessFile.
c.    The program compiles, but throws IOException because the file test.dat doesn't exist. The program displays IO exception.
d.    The program compiles and runs fine, but nothing is displayed on the console.
Key:c The problem is in line: new RandomAccessFile("test.dat", "r"); Because the file does not exist, you cannot open it for reading.

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20. With which I/O class can you append or update a file?

a. RandomAccessFile(),
b. OutputStream()
c. DataOutputStream()
d. None of the above
Key:a