IO中的字节流练习

1. FileInputStream  FileOutputStream通过字节流来读写文件

public static void main(String[] args) throws Exception {//将文件里写数据File f = new File("d:\\dmeo.txt");FileOutputStream output = new FileOutputStream(f);String s = "I Am Learning Java , 我在学习Java";byte[] b = s.getBytes(); //将String变为byte数组//output.write(b);write可以接收byte数组for (int i = 0; i < b.length; i++) {output.write(b[i]);}output.flush();output.close();//读取文件里数据FileInputStream input = new FileInputStream(f);//开辟一个文件大小的数组空间byte[] in = new byte[(int) f.length()];//将读取来的字节放入数组中for (int i = 0; i < in.length; i++) {in[i] = (byte) input.read(); }System.out.print(new String(in));input.close();}

2. BufferedInputStream BufferedOutPutStream 带有缓存的读写字节流

 public static void main(String[] args) throws Exception {//将文件里写数据File f = new File("d:\\dmeo.txt");BufferedOutputStream output = new BufferedOutputStream(new FileOutputStream(f));String s = "I Am Learning Java , 我在学习Java";byte[] b = s.getBytes();output.write(b); //默认会有512字节的缓存，当缓存存满时一次性向文件中写入output.flush(); output.close();BufferedInputStream input = new BufferedInputStream(new FileInputStream(f));byte[] in = new byte[(int)f.length()];for (int i = 0; i < in.length; i++) {in[i] = (byte)input.read();}System.out.println(new String(in));input.close(); }

2. DataInputStream DataOutputStream 可以读写基本数据类型的字节流

import java.io.*;//一个简单的人员类，只有姓名和年龄public class Person {private String name;private int age;public Person(String name ,int age){this.name = name;this.age = age;}public String getName(){return this.name;}public int getAge() {return this.age;}public static void main(String[] args) {//构造对象数组Person[] p1 = {new Person("Ryan",20),new Person("Tom",30),new Person("Jerry",15)};File f = new File("d:\\demo\\demo.txt");try {DataOutputStream output =  new DataOutputStream(new FileOutputStream(f));//写入数据for (int i = 0; i < p1.length; i++) {output.writeUTF(p1[i].getName()); //以UTF编码写入姓名output.writeInt(p1[i].getAge()); //以Int型写入年龄}output.flush();output.close();} catch (Exception e) {e.printStackTrace();}Person[] p2 = new Person[p1.length];try {//读出数据DataInputStream input = new DataInputStream(new FileInputStream(f));for (int i = 0; i < p1.length; i++) {String name =  input.readUTF(); //读出姓名int age  = input.readInt(); //读出年龄//重新构造person对象p2[i] = new Person(name,age);}                input.close();} catch (Exception e) {e.printStackTrace();}//检查是否还原正确for (int i = 0; i < p2.length; i++) {System.out.println("姓名：" + p2[i].getName() + " ；年龄：" + p2[i].getAge());}}}

2. PrintStream  将内存中的数据经过相应的转换后再输出

public static void main(String[] args){File f = new File("d:\\dmeo.txt");String studentName = "TOM";int age = 20;double totalScore = 600.0f;PrintStream ps = null;try {ps = new PrintStream(new FileOutputStream(f));} catch (FileNotFoundException e) {e.printStackTrace();}//格式化后输出ps.printf("姓名：%s , 年龄：%d , 总分：%3.1f",studentName,age,totalScore);}