Boolean type

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:"

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:"

public boolean isALessThanB (int a, int b)
{
    if (a < b)
        return true;
    else
        return false;
}

public boolean isALessThanB (int a, int b)
{
   boolean m = (a < b);
    if (m)
        return true;
    else
        return false;
}

public boolean isALessThanB (int a, int b)
{
    boolean m = (a < b);
    return m;
}

public boolean isALessThanB (int a, int b)
{
    return a < b;
}

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

Open

"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:"

"Could you give me more examples?"

"Sure:"

"Now, do some tasks."

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

Open

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

Open

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

Open