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Daraja

28 February 2021
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31-daraja. Daraja mavzusi bo'yicha suhbat savollariga javoblar

Ob'ekt Filehali mavjud bo'lmagan faylga mos kelishi mumkinmi?

Ha, agar siz katalog qiymatini konstruktorga o'tkazsangiz.

String dirPath = "/";
File f = new File(dirPath);
File[] files = f.listFiles();

Bu, masalan, fayllar qatorini olish uchun amalga oshiriladi.

public class MyClass {
    public static void main(String[] args) {
        boolean isObject = false;


        File file = new File("/");
        if (file instanceof Object){
            isObject = true;
        }
        boolean isFile = file.isFile(); // Tests whether the file denoted by this abstract pathname is a normal file.
Это из documentации
        System.out.println(isObject + " "+ isFile);

    }
}

Chiqish:

haqiqiy yolg'on

Filedan meros oladi object. Javob: ha! Fikrlaringizni kutaman.

Ob'ektni Fileturga qanday aylantirish mumkin Path?

UsultoPath();

toPath(); //Returns a java.nio.file.Path object constructed from the this abstract path.

Files klassi nima uchun kerak?

Biz sinfni asos qilib oldik File, unga ozgina yangi narsa qo'shdik, usullarni o'zgartirdik va oxirida uni ikkiga bo'ldik. Shunday qilib, endi ikkita yangi sinf mavjud - Pathva Files.

Path- bu, aslida, sinfning yangi analogidir Fileva Files- bu yordamchi sinf ( Arrays& classes bilan o'xshashlik bo'yicha Collections), sinfning barcha statik usullari unga o'tkazildi File. Bu OOP.M nuqtai nazaridan "to'g'riroq"

Hujjatlardan ba'zilari:

public final class Files
extends Object

Bu sinf faqat fayllar, kataloglar yoki boshqa turdagi fayllarda ishlaydigan statik usullardan iborat.
Ko'pgina hollarda, bu erda belgilangan usullar fayl operatsiyalarini bajarish uchun tegishli fayl tizimi provayderiga vakolat beradi.
Qanday arxivlash darslarini bilasiz?

Ushbu mavzu bo'yicha yaxshi maqola va undan parcha: Java'da arxivlash

Java spetsifikatsiyasida arxivlar bilan ishlash uchun ikkita paket mavjud - java.util.zipmos java.util.jarravishda zip va jar arxivlari uchun. Jar va zip formatlari o'rtasidagi farq faqat zip arxivining kengaytmasida. Paket konstruktorlarni amalga oshirish va sinf usulidan tashqari java.util.jarpaketga o'xshaydi . Faqat paketi quyida muhokama qilinadi . Barcha misollarni zip arxividan foydalanishga aylantirish uchun kodning hamma joyida Jar ni Zip bilan almashtiring.java.util.zipvoidputNextEntry(ZipEntry e)JarOutputStreamjava.util.jar

Arxivga katalogni qanday qo'shish mumkin?

O'zim uchun bu savolni tugallangan arxivga bo'sh katalog qo'shish deb tushundim. Men hech qanday ishlaydigan misol topmadim. Mana kod: (Bu arxivga istalgan faylni qo'yish mumkinligini aniq ko'rsatib turibdi, lekin bo'sh katalog bilan... Men qanday javob berishni bilmayman, StackOverFlow-ga yozmadim, bunday savol albatta bo'ladi. pastga ovoz berilgan) Agar kimdir biron bir taklif bo'lsa, yozing.

public class Main {
    public static void main(String[] args) {
        String[] myFiles = {"D:\\forJava\\MyArtifactName\\packForTest\\res2.txt",
                "D:\\forJava\\MyArtifactName\\packForTest\\res.txt",
                "D:\\forJava\\MyArtifactName\\packForTest\\res4.txt",
                "D:\\forJava\\MyArtifactName\\packForTest\\testDir\\"
                };
        String zipFile = "D:\\forJava\\MyArtifactName\\packForTest\\res.zip";
        ZipUtility zipUtil = new ZipUtility();
        try {
            zipUtil.zip(myFiles, zipFile);

        } catch (Exception ex) {
            // some errors occurred
            ex.printStackTrace();
        }
    }
}

Savol oxirgi testDir haqida, JVM uni olingan arxivga qo'ymaydi, boshqa barcha txt fayllari bilan u yaxshi ishlaydi.

ZipUtility.java:

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;

import java.io.FileOutputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.zip.ZipEntry;
import java.util.zip.ZipOutputStream;

public class ZipUtility {

    private static final int BUFFER_SIZE = 4096;

    public void zip(List<File> listFiles, String destZipFile) throws IOException {
        ZipOutputStream zos = new ZipOutputStream(new FileOutputStream(destZipFile));
        for (File file : listFiles) {
            if (file.isDirectory()) {
                zipDirectory(file, file.getName(), zos);
            } else {
                zipFile(file, zos);
            }
        }
        zos.flush();
        zos.close();
    }

    public void zip(String[] files, String destZipFile) throws IOException {
        List<File> listFiles = new ArrayList<File>();
        for (int i = 0; i < files.length; i++) {
            listFiles.add(new File(files[i]));
        }
        zip(listFiles, destZipFile);
    }

    private void zipDirectory(File folder, String parentFolder, ZipOutputStream zos) throws  IOException {
        for (File file : folder.listFiles()) {
            if (file.isDirectory()) {
                zipDirectory(file, parentFolder + "/" + file.getName(), zos);
                continue;
            }
            zos.putNextEntry(new ZipEntry(parentFolder + "/" + file.getName()));
            BufferedInputStream bis = new BufferedInputStream(
                    new FileInputStream(file));
            long bytesRead = 0;
            byte[] bytesIn = new byte[BUFFER_SIZE];
            int read = 0;
            while ((read = bis.read(bytesIn)) != -1) {
                zos.write(bytesIn, 0, read);
                bytesRead += read;
            }
            zos.closeEntry();
        }
    }

    private void zipFile(File file, ZipOutputStream zos)
            throws  IOException {
        zos.putNextEntry(new ZipEntry(file.getName()));
        BufferedInputStream bis = new BufferedInputStream(new FileInputStream(
                file));
        long bytesRead = 0;
        byte[] bytesIn = new byte[BUFFER_SIZE];
        int read = 0;
        while ((read = bis.read(bytesIn)) != -1) {
            zos.write(bytesIn, 0, read);
            bytesRead += read;
        }
        zos.closeEntry();
    }
}

Bu yerdan kod

Nima uchun ular kerak Properties?

Propertiesxususiyatlar faylidir. Uning tuzilishi: kalit - qiymat. Bunday fayllar bilan ishlash uchun Java-da sinf mavjud Properties, u meros qilib olinganHashTable<Object, Object>

Uni manipulyatsiya qilish haqida maqola bor - Java Properties fayl namunalari
Faylda ma'lumotlar qanday shaklda saqlanadi .properties?

Kalit - bu ma'no.

PropertiesOb'ektdagi ma'lumotlarni fayldan yuklagandan keyin o'zgartirish mumkinmi ?

Agar u dan meros bo'lib o'tgan bo'lsa HashMap, unda siz mumkin, faqat keyin siz ushbu faylga kiritilgan o'zgarishlarni yozishni bekor qilishingiz kerak bo'ladi. Buning uchun bir usul mavjud setProperty.

Mana kod:

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;

/**
 * Created by Роман on 12.09.2016.
 */
public class LoadAndSetProperties {

    public static void main(String[] args) {

        Properties prop = new Properties();
        InputStream input = null;
        try {

            input = new FileInputStream("D:\\forJava\\MyArtifactName\\packForTest\\config.properties");

            // load a properties file
            prop.load(input);

            // get the property value and print it out


            prop.setProperty("database", "ddfdfdfdfdf");
            System.out.print(prop.getProperty("database"));
        } catch (IOException ex) {
            ex.printStackTrace();
        } finally {
            if (input != null) {
                try {
                    input.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

}

Вывод:

ddfdfdfdfdf

Зачем нужен класс FileReader?

Java Docs:

public class FileReader
extends InputStreamReader

Convenience class for reading character files. The constructors of this class assume that the default character encoding and the default byte-buffer size are appropriate. To specify these values yourself, construct an InputStreamReader on a FileInputStream.

FileReader is meant for reading streams of characters.

Класс для чтения символов файлов. Конструкторы этого класса предполагают, что codeировка символов дефолтная и дефолтный размер буфера являются подходящими. Whatбы задать эти значения самостоятельно, следует построить InputStreamReader над FileInputStream. FileReader предназначен для считывания потоков символов.
Зачем нужен класс FileWriter?

public class FileWriter
extends OutputStreamWriter

Convenience class for writing character files. The constructors of this class assume that the default character encoding and the default byte-buffer size are acceptable. To specify these values yourself, construct an OutputStreamWriter on a FileOutputStream.

Whether or not a file is available or may be created depends upon the underlying platform. Some platforms, in particular, allow a file to be opened for writing by only one FileWriter (or other file-writing object) at a time. In such situations the constructors in this class will fail if the file involved is already open. FileWriter is meant for writing streams of characters.

Класс для записи символов файлов. Конструкторы этого класса предполагают, что codeировка символов дефолтная и дефолтный размер буфера являются приемлемым. Whatбы задать эти значения самостоятельно, следует построить OutputStreamWriter над FileOutputStream. Является ли файл доступен для записи, зависит от используемой платформы. Некоторые платформы разрешают держать файл для записи только одним FileWriter (or другого an object записи file), в одно время. FileWriter предназначен для записи потоков символов. Для написания потоков необработанных byteов, используйте FileOutputStream.

Эти классы (FileReader и FileWriter) специально ориентированы для работы с текстом и строками.