黑马程序员--第二十一天:io流的第四天

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//21-1import java.io.*;class ObjectStreamDemo{public static void writeObj() throws IOException {ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("object.object"));oos.writeObject(new Person("person1",19,"kr"));oos.close();}public static void readObj() throws Exception {ObjectInputStream ois = new ObjectInputStream(new FileInputStream("object.object"));Person p = (Person)ois.readObject();System.out.println(p);ois.close();}public static void main(String[] args)throws Exception {writeObj();readObj();System.out.println("Hello World!");}}//import java.io.*;class Person implements Serializable//用于类的标记{public static final long serialVersionUID = 42L;//用于类的标记。String name;transient int age;//transient 关键字,用于变量不序列化。static String country = "cn";  //static 的数据不能序列化。Person(String name, int age,String country){this.name = name;this.age = age;this.country = country;}public String toString(){return name+":"+age+":"+country;}}//21-2/*PipedInputStream: 从管道中读取PipedOutputStream: 写入管道*/import java.io.*;class  Read implements Runnable{private PipedInputStream in;Read(PipedInputStream in){this.in = in;}public void run (){try{byte[] buf = new byte[1024];System.out.println("读取前");int len = in.read(buf);System.out.println("读取后");String s = new String(buf,0,len);System.out.println(s);in.close();}catch (IOException e){throw new RuntimeException("管道读取流失败");}}}class Write implements Runnable{private PipedOutputStream out;Write(PipedOutputStream out){this.out = out;}public void run(){try{System.out.println("等待3秒");Thread.sleep(3000);//static 方法out.write("piped".getBytes());//out.close();}catch (Exception e){throw new RuntimeException("管道读取失败");}}}class PipedStreamDemo{public static void main(String[] args) throws IOException{PipedInputStream in = new PipedInputStream();PipedOutputStream out = new PipedOutputStream();in.connect(out);Read r = new Read(in);Write w = new Write(out);new Thread(r).start();//new Thread(w).start();System.out.println("Hello World!");}}/*21-3RandomAccessFile:该类不是IO体系的子类。而是直接继承自Object。但是它是IO包中的成员,因为它具备读和写功能。内部封装了一个数组,而且通过指针对数组的元素进行操作。可以通过getFilePointer获取指针位置。同时通过seek改变指针的位置。其实完成读写的原理就是内部封装了字节输入流和输出流。通过构造方法可以看出,该类只能操作文件。而且访问文件还有模式。"r","rw","rws","rwd"如果模式为只读,不会创建文件,会去读取一个已存在文件,如果该文件,如果该文件不存在,则会出现异常。如果模式为"rw",操作的文件不存在,会自动创建,如果存在不会覆盖。该类可以实现多线程下载只能操作文件而且该对象的构造函数要操作的文件不存在,会自动创建,且不覆盖已存在的文件。*/import java.io.*;class RandomAccessFileDemo{public static void main(String[] args) throws IOException{writeFile();readFile();System.out.println("Hello World!");}public static void readFile() throws IOException{RandomAccessFile raf = new RandomAccessFile("ran.txt","r");raf.seek(8);//raf.skipBytes(8);byte[] b = new byte[4];raf.read(b);String name = new String(b);int age = raf.readInt();System.out.println("name:" +name);System.out.println("age:" +age);}public static void writeFile() throws IOException{RandomAccessFile raf = new RandomAccessFile("ran.txt","rw");raf.write("人名".getBytes());//raf.write(97);//raf.write("97".getBytes());raf.writeInt(97);raf.write("随机".getBytes());raf.writeInt(255);raf.close();}}/*21-4可以用于操作基本数据类型*/import java.io.*;class DataStreamDemo {public static void main(String[] args) throws IOException{readData();System.out.println("Hello World!");}public static void writeUTFDemo()throws IOException{DataOutputStream dos = new DataOutputStream(new FileOutputStream("utfdata.txt"));dos.writeUTF("你好");//修改的utf-8编码dos.close();}public static void readUTFDemo()throws IOException{DataInputStream dis = new DataInputStream(new FileInputStream("utfdata.txt"));String s = dis.readUTF();//System.out.println(s);dis.close();}public static void readData() throws IOException {DataInputStream dis = new DataInputStream(new FileInputStream("data.txt"));int num = dis.readInt();boolean b = dis.readBoolean();double d = dis.readDouble();System.out.println(num);System.out.println(b);System.out.println(d);}public static void writeData() throws IOException {DataOutputStream dos = new DataOutputStream(new FileOutputStream("data.txt"));dos.writeInt(255);dos.writeBoolean(true);dos.writeDouble(9999.555);dos.close();}}/*21-5关闭 ByteArrayInputStream 无效。此类中的方法在关闭此流后仍可被调用,而不会产生任何 IOException。 ByteArrayInputStream: 在构造的时候,需要接收数据源,而且数据是一个字节数组。ByteArrayOutputStream: 在构造的时候,不需要接收目的,因为该对象中已经封装了可变长度的内部数组。这就是数组目的地。因为这两个流对象都操作数组,并没有使用系统资源,所以不用 close() 关闭。用流的读写思想来操作数组*///writeTo(OutputStream o)import java.io.*;class ByteArrayStream {public static void main(String[] args) {ByteArrayInputStream bis = new ByteArrayInputStream("abcdefg".getBytes());//ByteArrayOutputStream bos = new ByteArrayOutputStream();//int len = 0;while ((len = bis.read())!=-1){bos.write(len);}System.out.println(bos.size());//}}/*设备:键盘System.in/System.out 硬盘FileStream 内存ArrayStream*///21-6import java.io.*;class EncodeStream {public static void main(String[] args) throws IOException{readText();System.out.println("Hello World!");}public static void readText() throws IOException{InputStreamReader isr = new InputStreamReader(new FileInputStream("utf.txt"), "utf-8");//"gbk"char[] buf = new char[10];int len = isr.read(buf);String str = new String(buf,0,len);//System.out.println(str);isr.close();}public static void writeText() throws IOException{OutputStreamWriter osw = new OutputStreamWriter(new FileOutputStream("utf.txt"),"utf-8");osw.write("你好");osw.close();}}/*21-7编码:字符串变字节解码:字节变字符串String -->byte[]; str.getBytes(charsetName);byte[] -->String; new String(byte[],charsetName);Arrays.toString(b1)*/import java.util.*;class  EncodeDemo {public static void main(String[] args) throws Exception{String s = "你好";byte[] b1 = s.getBytes("utf-8");String s1 = new String (b1,"iso8859-1");byte[] b2 = s1.getBytes("iso8859-1");String s2 = new String (b2,"utf-8");System.out.println(s1);System.out.println(Arrays.toString(b1));System.out.println(s2);}}/*21-9有5个学生,每个学生有3门课成绩:从键盘输入以上数据(包括姓名,三门课成绩),输入的格式:如: zhangsan,30,40,60计算总成绩。并把学生的信息和计算出来的总分数由高到底的顺序保存到"stu.txt"中。*/import java.io.*;import java.util.*;class StudentInfoTool{public static void main(String[] args) throws IOException{Comparator<Student> cmp = Collections.reverseOrder();//CollectionsSet<Student> stus = StudentInfoTool.getStudents(cmp);StudentInfoTool.write2File(stus);System.out.println("Hello World!");}public static Set<Student> getStudents()throws IOException{return getStudents(null);}public static Set<Student> getStudents(Comparator<Student> cmp)throws IOException{BufferedReader bufr = new BufferedReader(new InputStreamReader(System.in));String line = null;Set<Student> stus = null;if (null==cmp)stus = new TreeSet<Student>();elsestus = new TreeSet<Student>(cmp);while ((line=bufr.readLine())!=null)//{if("over".equals(line))break;String[] info = line.split(",");Student stu = new Student(info[0],Integer.parseInt(info[1]),Integer.parseInt(info[2]),Integer.parseInt(info[3]));stus.add(stu);}bufr.close();return stus;}public static void write2File(Set<Student> stus)throws IOException{BufferedWriter bufw = new BufferedWriter(new FileWriter("stuinfo.txt"));for(Student stu: stus){bufw.write(stu.toString()+"\t");bufw.write(stu.getSum()+"");bufw.newLine();bufw.flush();}bufw.close();}}class Student implements Comparable<Student>//Comparable 接口{private String name;private int ma,cn,en;private int sum;Student(String name,int ma,int cn,int en){this.name = name;this.ma = ma;this.cn = cn;this.en = en;sum = ma + cn +en;}public int compareTo(Student s){int num = new Integer(this.sum).compareTo(new Integer(s.sum));if(0==num)return this.name.compareTo(s.name);return num;}public String getName(){return name;}public int getSum(){return sum;}public int hashCode(){//?????????????return name.hashCode() + sum*78;}public boolean equals(Object obj){//?????????????if(!(obj instanceof Student))throw new ClassCastException("类型不匹配");Student s = (Student)obj;return this.name.equals(s.name)&&this.sum==s.sum;}public String toString(){return "student{"+name+","+ma+","+cn+","+en+"}";}}/*必须自己重新写一次*/


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