> ## Documentation Index
> Fetch the complete documentation index at: https://docs.syntblaze.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Java Bitwise AND Assignment
The `&=` operator is a compound assignment operator that performs a bitwise AND (for integral types) or a logical AND (for boolean types) operation between the left and right operands, assigning the computed result back to the left operand.
## Syntax and Evaluation
```java theme={"dark"}
variable &= expression;
```
Internally, the Java compiler evaluates `a &= b` as `a = (T) (a & b)`, where `T` is the declared data type of `a`. This includes an implicit narrowing primitive conversion, which prevents compilation errors when operating on types smaller than `int` (such as `byte`, `short`, or `char`) that are automatically promoted to `int` during bitwise operations.
Crucially, Java semantics dictate that the left-hand operand in a compound assignment is evaluated **exactly once**. This distinguishes `a &= b` from its expanded form `a = (T) (a & b)` when the left operand contains side effects. For example, the expression `arr[i++] &= b` evaluates the array access and increments `i` only once, whereas `arr[i++] = (T) (arr[i++] & b)` would evaluate the array access and increment `i` twice.
## Behavior by Data Type
**1. Integral Types (`byte`, `short`, `int`, `long`, `char`)**
When applied to integral types, `&=` performs a bit-by-bit comparison of the binary representations of both operands. A bit in the resulting value is set to `1` if and only if the corresponding bits in both operands are `1`. Otherwise, the resulting bit is `0`.
```java theme={"dark"}
int a = 12; // Binary representation: 0000 1100
int b = 10; // Binary representation: 0000 1010
a &= b; // Bitwise AND operation
// 0000 1100
// 0000 1010
// ------
// 0000 1000 (Decimal: 8)
// a is now 8
```
**2. Boolean Type (`boolean`)**
When applied to boolean variables, `&=` performs a strict logical AND operation. The left operand is assigned `true` if and only if both the initial value of the left operand and the evaluated right operand are `true`. Otherwise, it is assigned `false`.
Unlike the conditional AND operator (`&&`), the `&=` operator **does not short-circuit**. The right-hand expression is always evaluated, regardless of the initial state of the left-hand operand.
```java theme={"dark"}
boolean flag = false;
// The method evaluateCondition() WILL be executed even though flag is already false.
flag &= evaluateCondition();
```
## Implicit Casting Mechanics
Because compound assignment operators automatically cast the result back to the left operand's type, `&=` bypasses the explicit casting requirement that a standard `&` operation would demand when working with narrower primitive types.
```java theme={"dark"}
byte b1 = 12;
byte b2 = 10;
// Standard bitwise AND requires explicit casting because operands are promoted to int
// b1 = b1 & b2; // Compilation error: incompatible types: possible lossy conversion from int to byte
b1 = (byte) (b1 & b2); // Compiles
// Compound assignment handles the cast implicitly
b1 &= b2; // Compiles successfully
```
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