"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:"

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);

"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;
}
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3
Task
New Java Syntax, level 3, lesson 10
Locked
Labels and numbers
Use the keyboard to enter an integer. Display a string description as follows: "Negative even number" - if the number is negative and even, "Negative odd number" - if the number is negative and odd, "Zero" - if the number is 0, "Positive even number" - if the number is positive and even, "Positive o

"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
! 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."

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3
Task
New Java Syntax, level 3, lesson 10
Locked
Describing numbers
Enter an integer from the keyboard in the range 1 - 999. Display a string description as follows: "even single-digit number" - if the number is even and has one digit, "odd single-digit number" - if the number is odd and has one digit, "even two-digit number" - if the number is even and has two digi
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3
Task
New Java Syntax, level 3, lesson 10
Locked
Positive number
Use the keyboard to enter three integers. Display the number of positive numbers in the original set. Here are some examples: a) if you enter the numbers -4 6 6 then we display 2 b) if you enter the numbers -6 -6 -3 then we display 0 c) if you enter the numbers 0 1 2 then we display 2
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3
Task
New Java Syntax, level 3, lesson 10
Locked
Positive and negative numbers
Use the keyboard to enter three integers. Display the number of positive and negative numbers in the original set in the following form: "Number of negative numbers: a", "Number of positive numbers: b", where a and b are the relevant values. Examples: a) if you enter the numbers: 2 5 6 then we displ