#TestPackage.java

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package lesson01;

import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 *
 * @author Diep.Tran
 */
public class TestPackage {
    public static void main(String[] args) {
        String s = "A";
        s += "B";
        s += "C";
        s += "D";
        s += "E";
        System.out.println("s = " + s);
        
        //Trong bai toan -> string -> join -> large
        StringBuilder builder = new StringBuilder();
        builder.append("123123");
        builder.append("sdfdsf");
        builder.append("srewr23");
        builder.append("234asd");
        builder.append("t43t3t");
        
        System.out.println(builder.toString());
        
        
        StringBuffer buffer = new StringBuffer();
        buffer.append("123123");
        buffer.append("sdfdsf");
        buffer.append("srewr23");
        buffer.append("234asd");
        buffer.append("t43t3t");
        
        System.out.println(buffer.toString());
        
        String s1 = "Sinh vien Aptech123 abcs aptech323 okk aptech666 akak";
        //Tim kiem xem trong chuoi s1 co chua bao nhieu chuoi tuan theo quy tac sau
        //ab -> a:[a-zA-Z]{3,10}, b:[0-9]{2,6}
        //Code nhu the nao??? for, if, else, ... => giai thuat.
        String s2 = "[a-zA-Z]{3,10}[0-9]{2,6}";
        Pattern p = Pattern.compile(s2);
        Matcher matcher = p.matcher(s1);
        
        while(matcher.find()) {
            System.out.println(matcher.start() + "-" + matcher.end() + "-" + matcher.group());
        }
    }
}

#Test.java

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package lesson01;

import java.util.Scanner;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 *
 * @author Diep.Tran
 */
public class Test {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        System.out.println("Nhap x=");
        int x = scan.nextInt();
        System.out.println("Nhap y=");
        int y = scan.nextInt();
        
        float s;
        try {
            s = Calculator.chia(x, y);
            System.out.println("s = " + s);
        } catch (Exception ex) {
            //Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);
            System.out.println(ex.getMessage());
        }
    }
}

#Main.java

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package lesson01;

import java.util.Scanner;

/**
 *
 * @author Diep.Tran
 */
public class Main {
    public static void main(String[] args) {
        //Exception
        //TH1 -> Giai phap -> Fix logic -> Chinh xac
        Scanner scan = new Scanner(System.in);
        System.out.println("Nhap x=");
        int x = scan.nextInt();
        System.out.println("Nhap y=");
        int y = scan.nextInt();
        //Cach 1 -> Fix logic
        if(y == 0) {
            System.out.println("Khong thuc hien phep chia cho 0"); 
        } else {
            int s = x/y;
            System.out.println("s = " + s);
        }
        //TH -> goi thu vien ben thu 3.
        try {
            //De khoi code -> ghi co the gay ra error
            int s = x/y;
            System.out.println("s = " + s);
        } catch(ArithmeticException e) {
            //Xay ra error -> nhay vao khu vuc nay
            System.out.println("ArithmeticException Exception ...");
        } finally {
            //Du code error - hay ko error -> deu goi vao day
            //Code dat trong finally -> giai phong tai nguyen
            System.out.println("finally ...");
        }
        
        //TH2
        int[] t = {1, 5, 2};//length: 3, index: 0 -> 2
        for (int i = 0; i < t.length; i++) {
            System.out.printf("\nt[%d]=%d", i, t[i]);
        }
    }
}

#Calculator.java

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package lesson01;

/**
 *
 * @author Diep.Tran
 */
public class Calculator {
    public static float cong(float x, float y) {
        return x + y;
    }
    
    public static float tru(float x, float y) {
        return x - y;
    }
    
    public static float nhan(float x, float y) {
        return x/y;
    }
    
    /**
     * Yeu cau nghiep vu -> TH y = 0 -> chuong trinh thong bao error -> Crash
     * @param x
     * @param y
     * @return 
     */
    public static float chia(float x, float y) throws Exception {
        if(y == 0) {
            throw new Exception("Error chia cho 0");
        }
        return x/y;
    }
}