Java boshlash

# Java dasturlash tilida dasturlash

java jdk o'rnatib olamiz.

main.java nomli fayl ochib ichiga quyidegilarni yozamiz:

public class Main{
  public static void main(String[] args){
    System.out.println("hello world");
  }
}

# Ma'lumotlar turlari

String  name       = "Adxamjon";
int     age        = 24;
float   myFloatNum = 5.99f;
char    myLetter   = 'D';
boolean myBool     = true;

# Qanday ma'lumot xotradan qancha joy egallashi

type	xotira	hajm
byte	1 byte	+-127
short	2 bytes	+-32 767
int	4 bytes	+-2 147 483 647
long	8 bytes	+-9 223 372 036 854 775 807
float	4 bytes	(,) keyin 6 to 7
double	8 bytes	(,) keyin 15
boolean	1 bit	true false
char	2 bytes	ASCII

# 1 turdan 2-turga o'tkazish

int myInt = 9;
double myDouble = myInt;

double myDouble2 = 9.78;
int myInt = (int) myDouble2;

# Matinlar uchun metdlar

String txt = "matin 'text'";
txt.length();
txt.toUpperCase() txt.toLowerCase()
txt.indexOf('text') // text boshlanish indexnini qaytaradi.

matinlar ichida ishlatish mumkin bo'lgan simvollar

code	simvol	nomi
'	'	tirnoq
"	"	qo'sh tirnoq
\	\	Backslash
\n		yangi qator
\r		Carriage Return
\t		Tab
\b		Backspace
\f		Form Feed

# Fayillar bilan ishlash

# Yayl yaratish

import java.io.File;

File myObj = new File("filename.txt");

Method	Type	Description
canRead()	Boolean	Tests whether the file is readable or not
canWrite()	Boolean	Tests whether the file is writable or not
createNewFile()	Boolean	Creates an empty file
delete()	Boolean	Deletes a file
exists()	Boolean	Tests whether the file exists
getName()	String	Returns the name of the file
getAbsolutePath()	String	Returns the absolute pathname of the file
length()	Long	Returns the size of the file in bytes
list()	String[]	Returns an array of the files in the directory
mkdir()	Boolean	Creates a directory

import java.io.File;  
// Import the File class
import java.io.IOException;  
// Import the IOException class to handle errors

public class CreateFile {
  public static void main(String[] args) {
    try {
      File myObj = new File("filename.txt");
      if (myObj.createNewFile()) {
        System.out.println("File created: " + myObj.getName());
      } else {
        System.out.println("File already exists.");
      }
    } catch (IOException e) {
      System.out.println("An error occurred.");
      e.printStackTrace();
    }
  }
}

Quyidegi ko'rinishdaham faylga murojat qilsa bo'ladi

File myObj = new File("C:\\Users\\MyName\\filename.txt");

# Yozish

import java.io.FileWriter;   // Import the FileWriter class
import java.io.IOException;  // Import the IOException class to handle errors

public class WriteToFile {
  public static void main(String[] args) {
    try {
      FileWriter myWriter = new FileWriter("filename.txt");
      myWriter.write("Files in Java might be tricky, but it is fun enough!");
      myWriter.close();
      System.out.println("Successfully wrote to the file.");
    } catch (IOException e) {
      System.out.println("An error occurred.");
      e.printStackTrace();
    }
  }
}

# O'qish

import java.io.File;  
// Import the File class
import java.io.FileNotFoundException;  
// Import this class to handle errors
import java.util.Scanner; 
// Import the Scanner class to read text files

public class ReadFile {
  public static void main(String[] args) {
    try {
      File myObj = new File("filename.txt");
      Scanner myReader = new Scanner(myObj);
      while (myReader.hasNextLine()) {
        String data = myReader.nextLine();
        System.out.println(data);
      }
      myReader.close();
    } catch (FileNotFoundException e) {
      System.out.println("An error occurred.");
      e.printStackTrace();
    }
  }
}

# fayl haqida ma'lumot

import java.io.File;  // Import the File class

public class GetFileInfo {
  public static void main(String[] args) {
    File myObj = new File("filename.txt");
    if (myObj.exists()) {
      System.out.println("File name: " + myObj.getName());
      System.out.println("Absolute path: " + myObj.getAbsolutePath());
      System.out.println("Writeable: " + myObj.canWrite());
      System.out.println("Readable " + myObj.canRead());
      System.out.println("File size in bytes " + myObj.length());
    } else {
      System.out.println("The file does not exist.");
    }
  }
}

# Faylni o'chirish

import java.io.File;  // Import the File class

public class DeleteFile {
  public static void main(String[] args) {
    File myObj = new File("filename.txt");
    if (myObj.delete()) {
      System.out.println("Deleted the file: " + myObj.getName());
    } else {
      System.out.println("Failed to delete the file.");
    }
  }
}

# Papkani o'chirish

import java.io.File;

public class DeleteFolder {
  public static void main(String[] args) {
    File myObj = new File("C:\\Users\\MyName\\Test");
    if (myObj.delete()) {
      System.out.println("Deleted the folder: " + myObj.getName());
    } else {
      System.out.println("Failed to delete the folder.");
    }
  }
}

# Javaning asosiy shart va takrorlanuvchi operatorlari

if(false){/*code*/}else{/*code*/}
switch(x){case 1: /*code*/ break; default: /*code*/};
while(false){}
do{/*code*/}while(false);
for(;;){/*code*/}
for(type var:vars){/*code*/} // foreach :
// break continue sikldan chiqsh o'tkazish

# Massivlar

int[] arr = {12,23}; // massiv hosil qilish
arr[0]; // massivni chaqirish
arr.length

int[][] arr={{},{},{}};

# Metodlar (Funksylar)

static void myMethod(String name, int age){/*code*/}  // void int
Math.max(x,y) // min(x,y) sqrt(x) abs(x) random() 0,0..1,0
final // konstanta

# OOP (class va obyektlar)

public class Car {// class yaratish
  int    modelYear;
  String modelName;

  public Car(int year, String name) {
    modelYear = year;
    modelName = name;
  }

  public static void metod(String[] args) {
    Car myCar = new Car(1969, "Mustang"); // obyekt yaratish
    
    System.out.println(myCar.modelYear + " " + myCar.modelName);
  }
} // public private protected

public abstract void study(); // abstract tanasiga ega bo'lmedi uni avlodi ega faqat

class Student extends Main{
  public void study(){/*code*/};
} //sherda

// inkapsulatsya privat qib get set bilan olish, this.name = name;

# Konsoldan kiritish

import java.util.Scanner;

// import package.name.Class;

Scanner myobj = new Scanner(System.in);

String userName = myobj.nextLine(); // malumot kiritng

// nextDouble() nextInt() nextChar()

# Shaxshiy paket yaratish

Java paketlari papkalar strukturasiga o'xshedi

masalan
  └── root
    └── mypack
      └── MyPackageClass.java

Чтобы создать пакет, используйте package ключевое слово:

MyPackageClass.java

package mypack;

class MyPackageClass {
  public static void main(String[] args) {
    System.out.println("This is my package!");
  }
}

Сохраните файл как MyPackageClass.java и скомпилируйте его:

C:\Users\Your Name>javac MyPackageClass.java
Затем скомпилируйте пакет:

C:\Users\Your Name>javac -d . MyPackageClass.java
Это заставляет компилятор создать пакет «mypack».

-d Ключевое слово указывает место для куда сохранить файл класса. Вы можете использовать любое имя каталога, например c:/user (windows), или, если вы хотите сохранить пакет в том же каталоге, вы можете использовать знак точки « .», как в примере выше.

Примечание. Имя пакета следует писать в нижнем регистре, чтобы избежать конфликта с именами классов.

Когда мы скомпилировали пакет в приведенном выше примере, была создана новая папка с именем «mypack».

Чтобы запустить файл MyPackageClass.java, напишите следующее:

C:\Users\Your Name>java mypack.MyPackageClass

Результат будет:
This is my package!

# interfeys

interface Animal{
  public void sleep();
}

class Pig implements Animal{}
// abstraksyaga o'xshedi public abstrackt

# enumiratsya

enum Level{
  LOW,
  MEDIUM,
  HIGH,
}

Level myVar = Level.MEDIUM;

// Level.values()
// Level.MEDIUM => MEDIUM

# massiv

import java.time.LocalDate;

LocalDate myObj = LocalDate.now();

import java.util.ArrayList;

ArrayList<String> arr = new ArrayList<String>();

arr.add("text");
arr.get(0);
arr.set(0, "text2");
arr.remove(0);
arr.clear();
arr.size(); // length

# Collecsya

import java.util.Collactions;

Collections.sort(arr);

import java.util.LinkedList;

LinkedList<int> arr = new LinkedList<int>(); // arrayList bilan birxil

addFirst()    // Adds an item to the beginning of the list.
addLast()     // Add an item to the end of the list
removeFirst() // Remove an item from the beginning of the list.
removeLast()  // Remove an item from the end of the list
getFirst()    // Get the item at the beginning of the list
getLast()     // Get the item at the end of the list

# Hato

try{}catch(Exception e){}finally{}    // hatoni tekshirish
throw new ArithmeticException("asd"); // hato qaytarish

# Patoklar bilan ishlash

public class Main extends Thread{
  public static void main(String[] args){
    Main thread = new Main();
    thread.start()
  }

  public void run(){}
}

# arrow function and foreach

import java.util.function.Consumer;

Consumer<Interger> method = (n) -> {System.out.println(n);};

arr.forEach(method);