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

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

1. 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) {
    
            }
        }
    }
   

   
   
   

2. 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) {
    
            }
        }
    }
   

   
   
   
   

3. 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());
            }
        } 
    }
   

   
   
   

4. 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);
        }
        }
    }
   

   

5. 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());
        }
    }
   

   

6. 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);
            } 
        }
    }
   

   

7. ABC

8. C

    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);
            }
        }
    }
   

   

9. 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);
            }
        }
    }
   

   
   
   
   

10. CD

    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:ookjava exists. Which of the following lines of code creates an object that represents the file? (Choose all that apply.)

  • A .new File("c:ookjava");
  • B .new File("c:ookjava");
  • 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

1. 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

2. 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

3. 教材学习中的问题和解决过程, 一个问题加1分

4. 代码调试中的问题和解决过程, 一个问题加1分

5. 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

6. 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

7. 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

• 如何解决无法成功git commit 和git push

• Java学习笔记(第8版)

• 《Java学习笔记(第8版)》学习指导

• 20155205 2016-2017-2 《Java程序设计》第4周学习总结