20155314 2016-2017-2 《Java程序设计》第7周学习总结

教材学习内容总结

了解Lambda语法
了解方法引用
了解Fucntional与Stream API
掌握Date与Calendar的应用
会使用JDK8新的时间API

教材学习中的问题和解决过程

课后习题

所谓“实践是检验认识真理性的唯一标准”，我在IntelliJ IDEA上把教材第三章课后练习题又敲了一

遍，给出了自己的答案，并加上了一些自己的分析，通过逐题进行代码调试实践的方式来深入对java类与对象的理解。小白在此恳请大家积极指出错误的地方(>_<)

9.4.1 选择题

CD 分析：

 import java.util.*;

 import java.util.ArrayList;

 public class Exercise9411 {

     public static void main(String[] args) {

         foreach(new HashSet());

         foreach(new ArrayList());

     }

     private static void foreach(Collection elements) {

         for(Object o : elements) {

         }

     }

 }

AB 分析：

 import java.util.*;

 //import java.util.ArrayList;

 public class Exercise9412 {

     public static void main(String[] args) {

         foreach(new HashSet() {

         });

     }

     private static void foreach(Iterable iterable) {

         for(Object o : iterable) {

         }

     }

 }

C 分析：

 import java.util.*;

 public class Exercise9413 {

     public static void main(String[] args) {

         foreach(new HashSet());

     }

     private static void foreach(Collection collection) {

         Iterator elements = collection.iterator();

         while(elements.hasNext()) {

             System.out.println(elements.next());

         }

     }

 }

D 分析：

 import java.util.*;

 class Student9414 {

     String number;

     String name;

     int score;

     Student9414(String number, String name, int score) {

         this.number = number;

         this.name = name;

         this.score = score;

     }

 }

 public class Exercise9414 {

     public static void main(String[] args) {

         Set<Student9414> students = new TreeSet<>();

         students.add(new Student9414("B1234", "Justin", 90));

         students.add(new Student9414("B5678", "Monica", 100));

         foreach(students);

     }

     private static void foreach(Collection<Student9414> students) {

         for(Student9414 student : students) {

         System.out.println(student.score);

     }

     }

 }

D 分析：

 import java.util.*;

 class Student9415 {

     String number;

     String name;

     int score;

     Student9415(String number, String name, int score) {

         this.number = number;

         this.name = name;

         this.score = score;

     }

 }

 public class Exercise9415 {

     public static void main(String[] args) {

         Set<Student9415> students = new HashSet<>();

         students.add(new Student9415("B1234", "Justin", 90));

         students.add(new Student9415("B5678", "Monica", 100));

         students.add(new Student9415("B1234", "Justin", 100));

         students.add(new Student9415("B5678", "Monica", 98));

         students.add(new Student9415("B5678", "Monica", 100));

         System.out.println(students.size());

     }

 }

A 分析：

 import java.util.*;

 public class Exercise9416 {

     public static void main(String[] args) {

         Set<Integer> numbers = new TreeSet<>();

         numbers.add(1);

         numbers.add(2);

         numbers.add(1);

         numbers.add(3);

         foreach(numbers);

     }

     private static void foreach(Collection<Integer> numbers) {

         for(Integer number : numbers) {

             System.out.println(number);

         }

     }

 }

 import java.util.*;

 public class Exercise9418 {

     public static void main(String[] args) {

         Set numbers = new TreeSet();

         numbers.add(1);

         numbers.add(2);

         numbers.add(1);

         numbers.add(3);

         for(Integer number : numbers) {

             System.out.println(number);

         }

     }

 }

C 分析：

 import java.util.*;

 public class Exercise9419 {

     public static void main(String[] args) {

         Set<Integer> numbers = new TreeSet<>();

         numbers.add(1);

         numbers.add(2);

         numbers.add(1);

         numbers.add(3);

         for(Integer number : numbers) {

             System.out.println(number);

         }

     }

 }

import java.util.*;

public class Exercise94110 {

    public static void main(String[] args) {

        Map<String, String> messages = new HashMap<>();

        messages.put("Justin", "Hello");

        messages.put("Monica", "HiHi");

        foreach(messages.values());

    }

    private static void foreach(Iterable<String> values) {

        for(String value : values) {

            System.out.println(value);

        }

    }

}

代码调试中的问题和解决过程

帮助20155324王鸣宇同学解决了Linux命令行下git commit和git push的问题~为此鸣宇还专门写了一篇博客记录下我们探索的详细过程～总之挺有成就感的嘻嘻( ̀⌄ ́)

如何解决无法成功git commit 和git push
关于20155322秦诗茂同学macOS下Vim编码问题（已解决，改为UTF-8即可）

代码托管

（statistics.sh脚本的运行结果截图）

上周考试错题总结

本周第二次采用了在蓝墨云班课上考试的形式，在45分钟的时间里需要作答20道选择题，而且还有不少多选题，甚至大多都是程序分析题，一道一道敲到电脑上再去运行肯定是来不及的(>_<)，更要命的是很多题不去跑程序的话我根本无从下手(>o<)所以还是老老实实学扎实才是万全之策啊～

下面哪条命令可以把 f1.txt 复制为 f2.txt ?
- A .cp f1.txt f2.txt
- B .copy f1.txt f2.txt
- C .cat f1.txt > f2.tx
- D .cp f1.txt | f2.tx
- E .copy f1.txt | f2.tx
正确答案： A C

我的答案： C

分析：copy是Windows下的命令。cat f1.txt > f2.tx 通过输出重定向实现了复制。

下面代码中共有（）个线程？

  public class ThreadTest {

      public static void main(String args[]){

          MyThread myThread =new MyThread();

          Thread t1=new Thread(myThread);

          Thread t2=new Thread(myThread);

          t1.start();

          t2.start();

      }

  }

  class MyThread extends Thread {

      ...

  }

A .1
B .2
C .3
D .4

正确答案： C

我的答案： B

分析：除了t1,t2, 不要忘了main所在的主线程。

调用线程的interrupt()方法，会抛出（）异常对象？
- A .IOException
- B .IllegalStateException
- C .RuntimeException
- D .InterruptedException
- E .SecurityException
正确答案： D E

我的答案： D

分析：查看帮助文档
Given an instance of a Stream, s, and a Collection, c, which are valid ways of creating a parallel stream? (Choose all that apply.)

给定一个Stream的实例s, 一个Collection的实例c, 下面哪些选项可以创建一个并行流？
- A .new ParallelStream(s)
- B .c.parallel()
- C .s.parallelStream()
- D .c.parallelStream()
- E .new ParallelStream(c)
- F .s.parallel()
正确答案： D F

我的答案： B

分析：D, F. There is no such class as ParallelStream, so A and E are incorrect. The method defined in the Stream class to create a parallel stream from an existing stream is parallel(); therefore F is correct and C is incorrect. The method defined in the Collection class to create a parallel stream from a collection is parallelStream(); therefore D is correct and B is incorrect.
Which of the following statements about the Callable call() and Runnable run() methods are correct? (Choose all that apply.)
- A .Both can throw unchecked exceptions.
- B .Callable takes a generic method argument.
- C .Callable can throw a checked exception.
- D .Both can be implemented with lambda expressions.
- E .Runnable returns a generic type.
- F .Callable returns a generic type.
- G .Both methods return void
正确答案： A C D F

我的答案： C E
What are some reasons to use a character stream, such as Reader/Writer, over a byte stream, such as InputStream/OutputStream? (Choose all that apply.)
- A .More convenient code syntax when working with String data
- B .Improved performance
- C .Automatic character encoding
- D .Built-in serialization and deserialization
- E .Character streams are high-level streams
- F .Multi-threading support
正确答案： A C

我的答案： F

分析：Character stream classes often include built-in convenience methods for working withString data, so A is correct. They also handle character encoding automatically, so C is also correct. The rest of the statements are irrelevant or incorrect and are not properties of all character streams.
Assuming zoo-data.txt is a multiline text file, what is true of the following method?

private void echo() throws IOException {

try (FileReader fileReader = new FileReader("zoo-data.txt");

BufferedReader bufferedReader = new BufferedReader(fileReader)) {

System.out.println(bufferedReader.readLine());

}

}
- A .It prints the first line of the file to the console.
- B .It prints the entire contents of the file.
- C .The code does not compile because the reader is not closed.
- D .The code does compile, but the reader is not closed.
- E .The code does not compile for another reason.
正确答案： A

我的答案： C

分析：This code compiles and runs without issue, so C and E are incorrect. It uses a try-with- resource block to open the FileReader and BufferedReader objects. Therefore, both get closed automatically, and D is incorrect. The body of the try block reads in the first line of the file and outputs it to the user. Therefore, A is correct. Since the rest of the file is not read, B is incorrect.
Assuming / is the root directory, which of the following are true statements? (Choose all that apply.)
- A ./home/parrot is an absolute path.
- B ./home/parrot is a directory.
- C ./home/parrot is a relative path.
- D .The path pointed to from a File object must exist.
- E .The parent of the path pointed to by a File object must exist.
正确答案： A

我的答案： E

分析：Paths that begin with the root directory are absolute paths, so A is correct and C is incorrect. B is incorrect because the path could be a file or directory within the file system. A File object may refer to a path that does not exist within the file system, so D and E are incorrect.
What is the result of executing the following code? (Choose all that apply.)

String line;

Console c = System.console();

Writer w = c.writer();

if ((line = c.readLine()) != null)

w.append(line);

w.flush();
- A .The code runs without error but prints nothing.
- B .The code prints what was entered by the user.
- C .An ArrayIndexOutOfBoundsException might be thrown.
- D .A NullPointerException might be thrown.
- E .An IOException might be thrown.
- F .The code does not compile.
正确答案： B D E

我的答案： C

分析：This is correct code for reading a line from the console and writing it back out to the console, making option B correct. Options D and E are also correct. If no con- sole is available, a NullPointerException is thrown. The append() method throws anIOException.
Which of the following are true? (Choose all that apply.)
- A .A new Console object is created every time System.console() is called.
- B .Console can only be used for reading input and not writing output.
- C .Console is obtained using the singleton pattern.
- D .When getting a Console object, it might be null.
- E .When getting a Console object, it will never be null.
正确答案： C D

我的答案： B D

分析：A Console object is created by the JVM. Since only one exists, it is a singleton, mak- ing option C correct. If the program is run in an environment without a console, System. console() returns null, making D also correct. The other statements about Console are incorrect.
Which classes will allow the following to compile? (Choose all that apply.)

InputStream is = new BufferedInputStream(new FileInputStream("zoo.txt"));

InputStream wrapper = new _____(is);
- A .BufferedInputStream
- B .FileInputStream
- C .BufferedWriter
- D .ObjectInputStream
- E .ObjectOutputStream
- F .BufferedReader
正确答案： A D

我的答案： A B

分析：The reference is for an InputStream object, so only a high-level input Stream class is permitted. B is incorrect because FileInputStream is a low-level stream that interacts directly with a file resource, not a stream resource. C and F are incorrect because you can- not use BufferedReader/BufferedWriter directly on a stream. E is incorrect because

the reference is to an InputStream, not an OutputStream. A and D are the only correct options. Note that a BufferedInputStream can be wrapped twice, since high-level streams can take other high-level streams.
Suppose that the file c:\book\java exists. Which of the following lines of code creates an object that represents the file? (Choose all that apply.)
- A .new File("c:\book\java");
- B .new File("c:\book\java");
- C .new File("c:/book/java");
- D .new File("c://book//java");
- E .None of the above
正确答案： B C

我的答案： A

分析：Option B is correct because Java requires a backslash to be escaped with another backslash. Option C is also correct because Java will convert the slashes to the right one when working with paths.

结对及互评

评分标准

正确使用Markdown语法（加1分）：
- 不使用Markdown不加分
- 有语法错误的不加分（链接打不开，表格不对，列表不正确...）
- 排版混乱的不加分
模板中的要素齐全（加1分）
- 缺少“教材学习中的问题和解决过程”的不加分
- 缺少“代码调试中的问题和解决过程”的不加分
- 代码托管不能打开的不加分
- 缺少“结对及互评”的不能打开的不加分
- 缺少“上周考试错题总结”的不能加分
- 缺少“进度条”的不能加分
- 缺少“参考资料”的不能加分
教材学习中的问题和解决过程, 一个问题加1分
代码调试中的问题和解决过程, 一个问题加1分
本周有效代码超过300分行的（加2分）
- 一周提交次数少于20次的不加分
其他加分：
- 周五前发博客的加1分
- 感想，体会不假大空的加1分
- 排版精美的加一分
- 进度条中记录学习时间与改进情况的加1分
- 有动手写新代码的加1分
- 课后选择题有验证的加1分
- 代码Commit Message规范的加1分
- 错题学习深入的加1分
- 点评认真，能指出博客和代码中的问题的加1分
- 结对学习情况真实可信的加1分
扣分：
- 有抄袭的扣至0分
- 代码作弊的扣至0分
- 迟交作业的扣至0分

点评模板：

博客中值得学习的或问题：
- xxx
- xxx
- ...
代码中值得学习的或问题：
- xxx
- xxx
- ...
基于评分标准，我给本博客打分：XX分。得分情况如下：xxx
参考示例

点评过的同学博客和代码

本周结对学习情况
- 20155323
- 结对照片
- 结对学习内容
  - 第六章继承与多态
  - 第三章基础语法
上周博客互评情况
- 20155318
- 20155314
- 20155210
- 20155301
- 20155208
- 20155305

感悟

也许是进入了瓶劲期了吧，感觉Java真的学不动了，难受(>_<)目前已经离老师布置的教学进程差了整整两章:(那又有什么办法呢只能老老实实按照自己的进度龟速向前爬呗～希望自己能在清明假期调整一下状态，争取迎头赶上吧……(｡ì _ í｡)

学习进度条

	代码行数（新增/累积）	博客量（新增/累积）	学习时间（新增/累积）	重要成长
目标	5000行	20篇	300小时
第一周	34/34	1/4	12/12
第二周	360/394	1/5	16/28
第三周	701/1018	1/6	19/ 47	代码量激增( ̀⌄ ́)
第四周	608/1375	1/7	18/55	①蹭了一节张健毅老师的Java课；②自己将数据结构课上所学的排序算法除了基数排序之外全部用C语言实现了一遍(｀_´)ゞ；③本次博客史无前例的长:)
第五周	1205/2580	1/8	9/64	蹭了一节张健毅老师的Java课
第六周	826/3339	1/9	8/72
第七周	/	2/11	13/85	①蹭了一节张健毅老师的Java课；②在写了无数篇实验报告之后还写了两篇博客！！

计划学习时间:10小时
实际学习时间:13小时

参考资料