A lecture snippet with a mentor as part of the Codegym University course. Sign up for the full course.
"Hi, Amigo. Let me tell you about a new data type. The boolean. Variables of this type can take only two values: true and false."
"How do we use it?"
"This type is implicitly used in many places. Just as any addition operation produces a number, the result of any comparison is a boolean. Here are some examples:"
|These two expressions are equivalent. The default value of a boolean variable is false.|
|The result of the comparison (either true or false) will be assigned to the variable
|There is no need to compare a logical (boolean) variable with true or false. The result of the comparison will be a boolean that matches the other variable. For example, true == true evaluates to true; true == false evaluates to false.|
|This method verifies that number a is less than number b.
Here are four equivalent comparisons. The last one is the most compact and correct. Always try to use compact notation.
"What if I want to write 0<a<b?"
"Java doesn't have a comparison operator that takes three operands. So, you would need to do it like this: (0<a) AND (a<b)."
"Do I write the word AND?"
"Wait. I'll explain that. Java has three logical operators: AND, OR and NOT. You can use them to construct conditions of varying complexity. You can use these operators only with boolean expressions. So, you can't write (a+1) AND (3), but (a>1)AND (a<3) is OK."
"The NOT operator is unary: it affects only the expression to the right. It's more like a minus sign before a negative number rather than a multiplication sign between two numbers."
"You can perform various operations on boolean (logical) variables."
"Let's take a look:"
|Logical operator||Java notation||Expression||Result|
|AND||&&||true && true||true|
|true && false||false|
|false && true||false|
|false && false||false|
|OR||||||true || true||true|
|true || false||true|
|false || true||true|
|false || false||false|
|Common combinations and expressions||m && !m||false|
|m || !m||true|
|! (a && b)||!a || !b|
|! (a || b)||!a && !b|
"Could you give me more examples?"
|Java notation||Logical notation|
|(a<3) && (a>0)||(a < 3) AND (a>0)|
|(a>10) || (a<100)||(a>10) OR (a<100)|
|(a<b) && (!(c<=d))||(a<b) AND (NOT (c<=d))|
"Now, do some tasks."