源码：labs/foundations/bitwise-operators-demo/src/BitwiseOperatorsBasicsDemo.java

• 原始路径：labs/foundations/bitwise-operators-demo/src/BitwiseOperatorsBasicsDemo.java
• 类型：java

/**
 * 位运算速查 Demo（通用，不绑 HashMap）。
 *
 * 理论文档：docs/00-foundations/01-bitwise-operators.md
 * HashMap 下标算法专题：labs/java/runtime-concurrency/map-concurrency-compare
 *
 * 运行：
 * cd labs/foundations/bitwise-operators-demo
 * javac -d out src/BitwiseOperatorsBasicsDemo.java
 * java -cp out BitwiseOperatorsBasicsDemo
 */
public class BitwiseOperatorsBasicsDemo {

    static final int READ = 1 << 0;
    static final int WRITE = 1 << 1;
    static final int EXEC = 1 << 2;

    public static void main(String[] args) {
        System.out.println("====== 位运算速查：符号与口诀 ======\n");
        printCheatSheet();

        System.out.println("\n====== 1. & 按位与 ——「掩码筛子，只留关心的位」======\n");
        demoAndMask();

        System.out.println("\n====== 2. | 按位或 ——「有 1 就 1，用来打开标志」======\n");
        demoOrFlags();

        System.out.println("\n====== 3. ^ 按位异或 ——「相同为 0，不同为 1」======\n");
        demoXorMix();

        System.out.println("\n====== 4. >>> 无符号右移 ——「右边扔掉，左边补 0」======\n");
        demoUnsignedShift();

        System.out.println("\n====== 5. >> 有符号右移 ——「负数左边补 1」======\n");
        demoSignedShift();

        System.out.println("\n====== 6. << 左移 ——「相当于乘 2 的幂」======\n");
        demoLeftShift();
    }

    static void printCheatSheet() {
        System.out.println("┌──────┬────────────────────┬──────────────────────────────────────┐");
        System.out.println("│ 符号 │ 名称               │ 常见用途                             │");
        System.out.println("├──────┼────────────────────┼──────────────────────────────────────┤");
        System.out.println("│  &   │ 按位与             │ 掩码：取出或清零某些位               │");
        System.out.println("│  |   │ 按位或             │ 置位：打开 READ / WRITE 等标志       │");
        System.out.println("│  ^   │ 按位异或           │ 翻转位、拌散数据                     │");
        System.out.println("│  ~   │ 按位非             │ 配合掩码做取反清零                   │");
        System.out.println("│  <<  │ 左移               │ 乘 2 的幂；构造 1<<n 标志位          │");
        System.out.println("│  >>  │ 有符号右移         │ 带符号整数除 2                       │");
        System.out.println("│ >>>  │ 无符号右移         │ 高位无符号地参与低位计算             │");
        System.out.println("└──────┴────────────────────┴──────────────────────────────────────┘");
        System.out.println("详细图解见：docs/00-foundations/01-bitwise-operators.md");
    }

    static void demoAndMask() {
        int value = 0b0000_0000_0000_0000_0000_0000_0000_1011; // 11
        int mask = 0x0F; // 低 4 位

        printBits("value", value);
        printBits("mask ", mask);
        printBits("value & mask", value & mask);

        System.out.println("比喻：mask 是筛子，只保留低 4 位。");
    }

    static void demoOrFlags() {
        int flags = 0;
        flags |= READ;
        flags |= WRITE;

        System.out.printf("flags = READ | WRITE → %d%n", flags);
        System.out.printf("含 READ?  %s%n", (flags & READ) != 0);
        System.out.printf("含 EXEC?  %s%n", (flags & EXEC) != 0);
    }

    static void demoXorMix() {
        int h = 0b0001_0010_0011_0100_0000_0000_1010_1011;
        int shifted = h >>> 16;
        int mixed = h ^ shifted;

        printBits("h        ", h);
        printBits("h >>> 16 ", shifted);
        printBits("h ^ (h>>>16)", mixed);

        System.out.println("比喻：把高位信息拌进低位（集合 hash 拌位同理，见 map-concurrency-compare）。");
    }

    static void demoUnsignedShift() {
        int h = 0x1234_ABCD;
        printBits("h       ", h);
        printBits("h >>> 16", h >>> 16);
        System.out.println(">>> 无符号：右边丢掉，左边补 0。");
    }

    static void demoSignedShift() {
        int negative = -1;
        printBits(" -1      ", negative);
        printBits(" -1 >> 4 ", negative >> 4);
        printBits(" -1 >>> 4", negative >>> 4);
        System.out.println("带符号除法用 >>；需要无符号语义时用 >>>。");
    }

    static void demoLeftShift() {
        System.out.println("1 << 3 = " + (1 << 3));
        System.out.println("5 << 2 = " + (5 << 2) + "  （5 × 4）");
    }

    static void printBits(String label, int value) {
        String bits = String.format("%32s", Integer.toBinaryString(value)).replace(' ', '0');
        System.out.printf("  %-14s = %11d  二进制: %s%n", label, value, bits);
    }
}