Java Notes (2) - Conditionals and Control Flow

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The note introduces how to use control flow and conditional statements in Java.

Java notes of open courses @Codecademy.

Boolean Operators

&&

: and operator

It returns a boolean value of

true

only when the expressions on both sides of

&&

are true.

||

: or operator

It returns a Boolean value of true when at least one expression on either side of

||

is true.

!

: not operator

It will return the opposite of the expression immediately after it. It will return

false

if the expression is true, and

true

if the expression is false.

Boolean Operator Precedence

!

>

&&

>

||

Every expression within parentheses is evaluated first.

Expressions are also read from left to right.

Conditional Expressions

if

statement

In Java, the keyword

if

is the first part of a conditional expression.

It is followed by a Boolean expression and then a block of code. If the Boolean expression evaluates to

true

, the block of code that follows will be run.

The

if

statement is not followed by a semicolon (

;

). Instead it uses curly braces (

{

and

}

) to surround the code block.

if

/

else

statement

The

if

/

else

conditional will run the block of code associated with the

if

statement if its Boolean expression evaluates to

true

.

Otherwise, if the Boolean expression evaluates to

false

, it will run the block of code after the

else

keyword.

if

/

elseif

/

else

statement

If the Boolean expression after the

if

statement evaluates to

true

, it will run the code block that directly follows.

Otherwise, if the Boolean expression after the

else if

statement evaluates to

true

, the code block that directly follow will run.

Finally, if all previous Boolean expressions evaluate to

false

, the code within the

else

block will run.

Ternary Conditional Statement

It can write

if

/

else

statements in a single line of code.

It from a Latin word that means “composed of three parts”:

A Boolean expression

A single statement that gets executed if the Boolean expression is true

A single statement that gets executed if the Boolean expression is false

E.g.,

(Boolean expression) ? 'T' : 'F';

Switch Statement

Java also provides a way to execute code blocks based on whether a block is equal to a specific value.

int restaurantRating = 3;

switch (restaurantRating) {

case 1: System.out.println("This restaurant is not my favorite.");
break;

case 2: System.out.println("This restaurant is good.");
break;

case 3: System.out.println("This restaurant is fantastic!");
break;

default: System.out.println("I've never dined at this restaurant.");
break;
}

The

break

statement will exit the

switch

statement after a condition is met. Without the

break

statement, Java will continue to check whether the value of

restaurantRating

matches any other cases.

The

default

case is printed only if

restaurantRating

is not equal to an int with the value of

1

,

2

, or

3

.

Review

Boolean Operators:

&&

,

||

, and

!

are used to build Boolean expressions and have a defined order of operations

Statements:

if

,

if

/

else

, and

if

/

else if

/

else

statements are used to conditionally execute blocks of code

Ternary Conditional: a shortened version of an

if

/

else

statement that returns a value based on the value of a Boolean expression

Switch: allows us to check equality of a variable or expression with a value that does not need to be a Boolean

External Resources

More Java Operators

Control Flow Statements