If an expression involving the Boolean & operator is evaluated, both operands are evaluated. Then the &operator is applied to the operand. When an expression involving the && operator is evaluated, the first operand is evaluated.
If the first operand returns a value of true then the second operand is evaluated. The && operator is then applied to the first and second operands. If the first operand evaluates to false, the evaluation of the second operand is skipped.