Toán tử logic và bitwise — short-circuit, cờ bit và thứ tự ưu tiên

boolean a = true, b = false;
System.out.println(a && b);  // false
System.out.println(a || b);  // true
System.out.println(!a);      // false

String s = null;

// AN TOAN: neu s == null thi khong goi s.isEmpty() (short-circuit)
if (s != null && s.isEmpty()) {
    System.out.println("Chuoi rong");
}

// NGUY HIEM: & khong short-circuit -- luon evaluate ca hai ve
// if (s != null & s.isEmpty())  // NPE neu s == null!

// Short-circuit trong OR: neu isAdmin() tra true, checkPermission() khong chay
boolean coQuyen = isAdmin() || checkPermission(userId);

int diem = 75;
String ketQua = (diem >= 50) ? "Dat" : "Roi";
System.out.println(ketQua);  // Dat

// Thay the if/else don gian -- gon hon
int max = (a > b) ? a : b;

// TRANH: nested ternary -- kho doc
String muc = (diem >= 90) ? "Xuat sac" : (diem >= 70) ? "Gioi" : (diem >= 50) ? "Trung binh" : "Roi";

// NEN: if/else if ro rang hon
String muc;
if      (diem >= 90) muc = "Xuat sac";
else if (diem >= 70) muc = "Gioi";
else if (diem >= 50) muc = "Trung binh";
else                 muc = "Roi";

int a = 5;  // binary: 0101
int b = 3;  // binary: 0011

System.out.println(a & b);   // 0001 = 1
System.out.println(a | b);   // 0111 = 7
System.out.println(a ^ b);   // 0110 = 6
System.out.println(~a);      // ...11111010 = -6 (two's complement)
System.out.println(1 << 3);  // 0001 << 3 = 1000 = 8 (nhan 2^3)
System.out.println(8 >> 1);  // 1000 >> 1 = 0100 = 4 (chia 2)

// Dinh nghia flags (moi flag la mot bit rieng)
static final int FLAG_READ    = 0b001;  // bit 0 = 1
static final int FLAG_WRITE   = 0b010;  // bit 1 = 2
static final int FLAG_EXECUTE = 0b100;  // bit 2 = 4

int quyen = FLAG_READ | FLAG_WRITE;  // 0b011 = 3 (co ca READ va WRITE)

// Kiem tra mot flag
boolean coRead = (quyen & FLAG_READ) != 0;    // true
boolean coExec = (quyen & FLAG_EXECUTE) != 0; // false

// Bat them flag
quyen |= FLAG_EXECUTE;  // them EXECUTE

// Tat flag
quyen &= ~FLAG_WRITE;   // xoa WRITE (AND voi NOT WRITE)

// Toggle flag
quyen ^= FLAG_READ;     // bat neu tat, tat neu bat

// Kiem tra so chan: bit cuoi == 0
boolean laSoChan = (n & 1) == 0;

// Chia doi nhanh bang shift (chi dung voi so duong)
int halved = n >> 1;  // tuong duong n / 2 nhung nhanh hon

int negative = -8;  // binary: 11111111111111111111111111111000

System.out.println(negative >> 1);   // -4: dich phai giu bit dau (1)
System.out.println(negative >>> 1);  // 2147483644: dich phai dien 0 vao bit cao nhat

// Khong ngoac -- dua vao precedence
int result = 2 + 3 * 4;   // = 14 (3*4 truoc, roi cong 2)

// Ro rang hon voi ngoac
int result2 = 2 + (3 * 4); // = 14 -- cung ket qua, ro hon
int result3 = (2 + 3) * 4; // = 20 -- thay doi thu tu

// Ket hop comparison va logical
boolean check = x > 0 && x < 100;  // > va < truoc &&

public class LogicBitwiseDemo {
    static final int FLAG_READ    = 0b001;
    static final int FLAG_WRITE   = 0b010;
    static final int FLAG_EXECUTE = 0b100;

    public static void main(String[] args) {

        // --- Short-circuit null safe ---
        String s = null;
        if (s != null && s.isEmpty()) {
            System.out.println("Chuoi rong");
        } else {
            System.out.println("s la null hoac co noi dung");
        }

        // --- Bitwise flags ---
        int permissions = FLAG_READ | FLAG_WRITE;
        System.out.println("Co READ: " + ((permissions & FLAG_READ) != 0));       // true
        System.out.println("Co EXECUTE: " + ((permissions & FLAG_EXECUTE) != 0)); // false

        // Kiem tra so chan bang bitwise
        for (int i = 0; i < 6; i++) {
            System.out.println(i + " la so " + ((i & 1) == 0 ? "chan" : "le"));
        }

        // --- Shift: giu dau vs dien 0 ---
        int negative = -8;
        System.out.println(negative >> 1);   // -4
        System.out.println(negative >>> 1);  // 2147483644

        // --- Ternary ---
        int score = 75;
        String result = (score >= 50) ? "Pass" : "Fail";
        System.out.println("Ket qua: " + result);
    }
}