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互评作业

  1. 字节流与二进制文件
    ==========================

我的代码

class Student {
	private int id;
	private String name;
	private int age;
	private double grade;

	public Student() {

	}
	public Student(int id, String name, int age, double grade) {
		this.id = id;
		this.setName(name);
		this.setAge(age);
		this.setGrade(grade);
	}
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		if (name.length() > 10) {
			throw new IllegalArgumentException("name's length should <=10 " + name.length());
		}
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		if (age <= 0) {
			throw new IllegalArgumentException("age should >0 " + age);
		}
		this.age = age;
	}
	public double getGrade() {
		return grade;
	}
	public void setGrade(double grade) {
		if (grade < 0 || grade > 100) {
			throw new IllegalArgumentException("grade should be in [0,100] " + grade);
		}
		this.grade = grade;
	}
	@Override
	public String toString() {
		return "Student [id=" + id + ", name=" + name + ", age=" + age + ", grade=" + grade + "]";
	}
}

public class Main {
	public static void main(String[] args)
          {         
             String fileName="d:\\student.data";
              try(DataOutputStream dos=new DataOutputStream(new FileOutputStream(fileName)))
             {
                  Student[] stu=new Student[3];
                  stu[0]=new Student(1,"zhangsan",19,65.0);
                  stu[1]=new Student(2,"lisi",19,75.0);
                  stu[2]=new Student(3,"wangwu",20,85.0);
                  for(Student stu1:stu) {
                     dos.writeInt(stu1.getId());
                     dos.writeUTF(stu1.getName());
                     dos.writeInt(stu1.getAge());
                     dos.writeDouble(stu1.getGrade());
                }
                 
            } catch (FileNotFoundException e) {
                e.printStackTrace();
                 System.out.println("1");
            } catch (IOException e) {
                 e.printStackTrace();
               System.out.println("2");
            }
            try(DataInputStream dis=new DataInputStream(new FileInputStream(fileName)))
             {
                while(dis!=null) {
                    int id=dis.readInt();
                    String name=dis.readUTF();
                    int age=dis.readInt();
                     double grade=dis.readDouble();
                     Student stu=new Student(id,name,age,grade);
                    System.out.println(stu);
                }
                 
                
            } catch (FileNotFoundException e) {
                e.printStackTrace();
                 System.out.println("3");
            } catch (IOException e) {
                e.printStackTrace();
                System.out.println("4");
           }
             
         }

我的总结

学会了使用try..with...resouces关闭资源,原来可以用用finally来关闭文件,但也要判断是否可以关闭资源的问题。而用try…with…resource可以解决该问题,当try语句块运行结束时,相应资源会被自动关闭。这是因为FileInputStream 实现了java中的java.lang.AutoCloseable。所有实现了这个接口的类都可以在try-with-resources结构中使用。 
  1. 字符流与文本文件
    ==========================

我的代码

public class Main {
	public static void main(String[] args) throws IOException {
		String FileName = "D:\\TSBrowserDownloads\\Students.txt";
		BufferedReader br = null;
		try {
			br = new BufferedReader(new InputStreamReader(new FileInputStream(FileName), "UTF-8"));
			String line = null;
			while ((line = br.readLine()) != null)
				System.out.println(line);
		} finally {
			if (br != null) {
				br.close();
			}
		}
	}

}
public static void ListreadStudents(String fileName){
             ArrayList<Student> StudentList=new ArrayList<Student>();
            BufferedReader br = null;
            try {
                br = new BufferedReader(new InputStreamReader(new FileInputStream(fileName),"UTF-8"));
               while(br!=null) {
                    String line=br.readLine();
                    String[] stu=line.split("\\s+");
                    int id=Integer.parseInt(stu[0]);
                     String name=stu[1];
                     int age=Integer.parseInt(stu[2]);
                     double grade=Double.parseDouble(stu[3]);
                     Student Stu=new Student(id,name,age,grade);
                    StudentList.add(Stu);          
                }                
            } finally{
                if (br!=null){
                    br.close();
                 }
             }
 }

我的总结

要以UTF-8打开文件,否则会乱码。BufferedReader只用read和ReadLine方法,得用实验提到的"\\s+"的方法将读到的一整行用分隔符来分开,再用类型转换来读。

2.缓冲流

我的代码

public class test {
	@Test
	public void test() {
		String FILENAME = "test.txt";
		long begin = System.currentTimeMillis();
		Scanner scanner = null;
		try {
			scanner = new Scanner(new File(FILENAME));
			while (scanner.hasNextLine()) {// 只是读出每一行,不做任何处理
				scanner.nextLine();
			}
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} finally {
			scanner.close();
		}
		long end = System.currentTimeMillis();
		System.out.println("last " + (end - begin));
		System.out.println("read using Scanner done");
	}

	@Test
	public void Bufftest() {
		String FILENAME = "test.txt";
		long begin = System.currentTimeMillis();
		BufferedReader br = null;
		try {
			br = new BufferedReader(new FileReader(new File(FILENAME)));
			while (br.readLine() != null) {
			}
			;// 只是读出,不进行任何处理
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			try {
				br.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
		long end = System.currentTimeMillis();
		System.out.println("last " + (end - begin));
		System.out.println("read using BufferedReader done");
	}
}

我的总结

缓冲流BufferedReader的方法要比Scanner的方法快很多

posted on 2019-11-26 22:24  haiqingz  阅读(253)  评论(0编辑  收藏  举报