Java 運算符全解析：算術、關系、位運算符核心差異與實戰陷阱

二、關系運算符

六大運算符

>、<、>=、<=、==、!=

與 C 語言的關鍵差異

代碼驗證

public class RelationalDemo {
    public static void main(String[] args) {
        System.out.println("10 > 5  = " + (10 > 5));   // true
        System.out.println("10 >= 5 = " + (10 >= 5));  // true
        System.out.println("10 < 5  = " + (10 < 5));   // false
        System.out.println("10 <= 5 = " + (10 <= 5));  // false
        System.out.println("10 == 5  = " + (10 == 5));  // false
        System.out.println("10 != 5  = " + (10 != 5));  // true
    }
}

三、位運算符

四大核心運算符

真值表速查

public class BitwiseTruthTable {
    public static void main(String[] args) {
        System.out.println("--- AND ---");
        System.out.println("0 & 0 = " + (0 & 0));
        System.out.println("0 & 1 = " + (0 & 1));
        System.out.println("1 & 0 = " + (1 & 0));
        System.out.println("1 & 1 = " + (1 & 1));
        
        System.out.println("\n--- OR ---");
        System.out.println("0 | 0 = " + (0 | 0));
        System.out.println("0 | 1 = " + (0 | 1));
        System.out.println("1 | 0 = " + (1 | 0));
        System.out.println("1 | 1 = " + (1 | 1));
        
        System.out.println("\n--- XOR ---");
        System.out.println("0 ^ 0 = " + (0 ^ 0));
        System.out.println("0 ^ 1 = " + (0 ^ 1));
        System.out.println("1 ^ 0 = " + (1 ^ 0));
        System.out.println("1 ^ 1 = " + (1 ^ 1));
        
        System.out.println("\n--- NOT ---");
        System.out.println("~0 = " + (~0)); // -1
        System.out.println("~1 = " + (~1)); // -2
    }
}

位運算實戰技巧

• 判斷奇偶：(n & 1) == 1 比 n % 2 != 0 更快
• 乘除 2 的冪次：n << 1 ≡ n*2，n >> 1 ≡ n/2
• 交換變量：異或法 a ^= b; b ^= a; a ^= b;（前文詳述）
• 權限掩碼：if (permission & READ) != 0 檢查讀權限

四、總結建議

1. 算術運算：注意整數除法截斷、強制轉型精度損失
2. 關系運算：牢記結果是 boolean，不可當 int 用
3. 位運算：掌握真值表，善用位運算優化性能敏感代碼
4. 短路原則：&& || 遇真/假即停，可用於防空指針 obj != null && obj.method()