Course New Java Syntax - Lecture: Boolean type

"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:"


boolean m;
boolean m = false;
if (a > b)
     System.out.println(a);
boolean m = (a > b);
 if (m)
     System.out.println(a);
boolean m = (a > b);
 if (m == true)
     System.out.println(a);
boolean m = (a > b);
 if (m)
     System.out.println(a);

"More examples:"

	Code	Explanation
1	`public boolean isALessThanB (int a, int b) { if (a < b) return true; else return 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.
2	`public boolean isALessThanB (int a, int b) { boolean m = (a < b); if (m) return true; else return false; }`
3	`public boolean isALessThanB (int a, int b) { boolean m = (a < b); return m; }`
4	`public boolean isALessThanB (int a, int b) { return a < b; }`

"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."

"Like what?"

"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
NOT	!	! true	false
NOT	!	! false	true
Common combinations and expressions		m && !m	false
		m \|\| !m	true
		! (a && b)	!a \|\| !b
		! (a \|\| b)	!a && !b

"Could you give me more examples?"

"Sure:"

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."

Comments (3)

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Vadym

Level 34

27 December 2022, 03:57

I solved this task same way but only with another variables names and I'v got error...strange a little bit

Anonymous #3179019

Level 30

6 October 2022, 12:38

Java code convention by Oracle explicitly states that using if statements without braces should be avoided:

if (m)
    return true;
else
    return false;

Avoid such form! Use instead:

if (m) {
    return true;
}
else {
    return false;
}

See Code convention

Andrei Karavai

Level 29

24 October 2023, 15:35

I saw tons of ifs without braces on Leetcode. They try to save every line with that. I'd prefer this way to keep track of code blocks and to be able to find opening and closing braces easily:

	Code	Explanation
1	`boolean m;`	These two expressions are equivalent. The default value of a boolean variable is false.
2	`boolean m = false;`
3	`if (a > b) System.out.println(a);`	The result of the comparison (either true or false) will be assigned to the variable `m`. The condition is satisfied if the expression evaluates to true.
4	`boolean m = (a > b); if (m) System.out.println(a);`
5	`boolean m = (a > b); if (m == true) System.out.println(a);`	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.
6	`boolean m = (a > b); if (m) System.out.println(a);`