1. Introduction

In Java, & and && are operators used for evaluating boolean expressions. The & operator is the bitwise AND operator when used with numbers and the logical AND operator when used with boolean values. The && operator is the short-circuit logical AND operator that evaluates boolean expressions only.

2. Key Points

1. & evaluates both sides of the operation regardless of the result of the first one when used as a logical AND operator.

2. && evaluates the second operand only if the first operand is true.

3. & is also a bitwise operator for integer types.

4. && provides performance benefits by not evaluating the right-hand side expression if it's not necessary.

3. Differences

& (AND) && (Short-circuit AND)
Always evaluates both operands. Evaluates the second operand only if the first is true.
Can be used as both a bitwise and a logical operator. Used only as a logical operator.
No performance optimization in Boolean expressions. Can provide performance optimization in boolean expressions.

4. Example

``````
public class AndOperators {
public static void main(String[] args) {
int a = 4; // 100 in binary
int b = 5; // 101 in binary

// Step 1: Using the bitwise AND operator
int result = a & b; // This will be 100 in binary or 4 in decimal
System.out.println("Bitwise AND result: " + result);

// Step 2: Using the logical AND operator
boolean firstCondition = true;
boolean secondCondition = false;

// The & operator evaluates both conditions
if (firstCondition & secondCondition) {
System.out.println("Both conditions are true.");
} else {
System.out.println("Using & operator: one or both conditions are false.");
}

// The && operator does not evaluate the second condition because the first is false
if (firstCondition && secondCondition) {
System.out.println("Both conditions are true.");
} else {
System.out.println("Using && operator: one or both conditions are false.");
}
}
}

``````

Output:

```Bitwise AND result: 4
Using & operator: one or both conditions are false.
Using && operator: one or both conditions are false.
```

Explanation:

1. The bitwise AND operation between a and b results in 4, as it operates on each bit of the integers.

2. The logical AND & checks both firstCondition and secondCondition even though it's clear that the combined expression cannot be true if the first condition is false.

3. The short-circuit AND && checks firstCondition, finds it to be true, and then checks secondCondition. Since secondCondition is false, it stops and returns false.

5. When to use?

- Use & as a bitwise operator when you're working with bits or as a logical operator when you need to evaluate both conditions for their side effects.

- Use && when evaluating boolean expressions where the second condition does not need to be evaluated if the first one is false, for performance reasons.