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IO流是Java程序中处理数据输入输出的核心机制，主要用于文件操作。根据数据类型的不同，可以分为字节流和字符流；根据数据流向的不同，又分为输入流和输出流。程序通过输入流读取数据，输出流写入数据进行处理。Java的IO包中，字节流由InputStream和OutputStream类表示，字符流由Reader和Writer类表示。具体分类可参考下图。

字节流

在JDK中，InputStream和OutputStream是字节流的顶级父类，所有字节输入流都继承自InputStream，所有字节输出流都继承自OutputStream。这些类用于读写文件时操作的字节数据。

字符流

对于处理字符数据，直接使用InputStream和OutputStream不太方便，JDK提供了字符流。字符流的顶级父类是Reader和Writer。Reader用于从文件或其他设备读取字符，Writer用于向目标设备写入字符。字符流更适合处理文本文件。

File类

File类用于操作文件和目录，提供了路径管理和文件操作的方法。常用方法包括文件存在性检查、创建、删除等。以下是File类的常用方法示例：

• bool exists(): 判断文件或目录是否存在。
• void createDir(): 创建目录。
• void delete(): 删除文件或目录。

代码示例

以下是管理车库的Java代码示例，展示了文件操作的实际应用：

import java.io.*;import java.util.ArrayList;import java.util.Arrays;import java.util.List;class Car {    public String carNum;    public String carBrand;    public String carModel;    public Car(String carNum, String carBrand, String carModel) {        this.carNum = carNum;    this.carBrand = carBrand;    this.carModel = carModel;    }    @Override    public String toString() {        return carNum + "，" + carBrand + "，" + carModel;    }}class ManagePark {    public Boolean findCarByCarNum(Car car) throws IOException {        if(car == null) {            return false;        }        FileReader fileReader = new FileReader("e:\\MyCarPark.txt");        BufferedReader bufferedReader = new BufferedReader(fileReader);        String findCar = bufferedReader.readLine();        while (findCar != null) {            String[] strings = findCar.split("，");            if(strings[0].equals(car.carNum)) {                return true;            }            findCar = bufferedReader.readLine();        }        bufferedReader.close();        fileReader.close();        return false;    }    public void stopAtPark(Car car) throws IOException {        if(car == null) {            return;        }        if(findCarByCarNum(car)) {            return;        }        FileWriter fileWriter = new FileWriter("e:\\MyCarPark.txt", true);        BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);        String carString = car.toString();        bufferedWriter.newLine();        bufferedWriter.write(carString);        bufferedWriter.close();        fileWriter.close();    }    public void LeavePark(Car car) throws IOException {        if(!findCarByCarNum(car)) {            return;        }        List
   
     listCar = new LinkedList<>();        FileReader fileReader = new FileReader("e:\\MyCarPark.txt");        BufferedReader bufferedReader = new BufferedReader(fileReader);        String findCar = bufferedReader.readLine();        while (findCar != null) {            String[] strings = findCar.split("，");            if(strings.length > 1) {                if(!strings[0].equals(car.carNum)) {                    listCar.add(new Car(strings[0], strings[1], strings[2]));                }            }            findCar = bufferedReader.readLine();        }        bufferedReader.close();        fileReader.close();        FileWriter fileWriter = new FileWriter("e:\\MyCarPark.txt");        BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);        for(Car c : listCar) {            String sCar = c.toString();            bufferedWriter.newLine();            bufferedWriter.write(sCar);        }        bufferedWriter.close();        fileWriter.close();    }    public Car[] getCarByBrand(String brand) throws IOException {        ArrayList
    
      carList = new ArrayList<>();        FileReader fileReader = new FileReader("e:\\MyCarPark.txt");        BufferedReader bufferedReader = new BufferedReader(fileReader);        String findCar = bufferedReader.readLine();        while (findCar != null) {            String[] strings = findCar.split("，");            if(strings.length > 1) {                if(strings[1].equals(brand)) {                    carList.add(new Car(strings[0], strings[1], strings[2]));                }            }            findCar = bufferedReader.readLine();        }        bufferedReader.close();        fileReader.close();        return carList.toArray(new Car[0]);    }    public void displayMyParkCar() throws IOException {        FileReader fileReader = new FileReader("e:\\MyCarPark.txt");        BufferedReader bufferedReader = new BufferedReader(fileReader);        String findCar = bufferedReader.readLine();        while (findCar != null) {            System.out.println(findCar);            findCar = bufferedReader.readLine();        }        System.out.println();        bufferedReader.close();        fileReader.close();    }}public class MyCarParkTest {    public static void main(String[] args) throws IOException {        try {            Car car = new Car("陕A33333", "宝马", "宝马X6");            Car car1 = new Car("陕A66666", "奔驰", "黑色G500");            ManagePark managePark = new ManagePark();            System.out.println("===初始车库===");            managePark.displayMyParkCar();            System.out.println("===找是否有陕A33333===");            System.out.println(managePark.findCarByCarNum(car));            System.out.println("===找是否有陕A66666===");            System.out.println(managePark.findCarByCarNum(car1));            System.out.println("===找车库中所有劳斯莱斯的车===");            Car[] cars = managePark.getCarByBrand("劳斯莱斯");            System.out.println(Arrays.toString(cars));            System.out.println();            System.out.println("===陕A66666离开车库陕A33333进入车库===");            managePark.LeavePark(car1);            managePark.stopAtPark(car);            System.out.println("===最终车库===");            managePark.displayMyParkCar();        } catch (IOException e) {            e.getStackTrace();        }    }}
    
   

运行结果

===初始车库===陕A66666，奔驰，黑色G500陕A88888，劳斯莱斯，劳斯莱斯幻影陕A00000，迈巴赫，迈巴赫62陕A11111，保时捷，保时捷911陕A99999，劳斯莱斯，劳斯莱斯古斯特===找是否有陕A33333===false===找是否有陕A66666===true===找车库中所有劳斯莱斯的车===[陕A88888，劳斯莱斯，劳斯莱斯幻影, 陕A99999，劳斯莱斯，劳斯莱斯古斯特]===陕A66666离开车库陕A33333进入车库===———===最终车库===陕A88888，劳斯莱斯，劳斯莱斯幻影陕A00000，迈巴赫，迈巴赫62陕A11111，保时捷，保时捷911陕A99999，劳斯莱斯，劳斯莱斯古斯特陕A33333，宝马，宝马X6