java(6)---CONDITIONALS AND CONTROL FLOW

CONDITIONALS AND CONTROL FLOW

to write Java programs that can follow different sets of instructions depending on the values that we provide to them. This is called control flow.

• There are three Boolean operators that we will explore. Let’s start with the first one: and.

1. The and operator is represented in Java by &&.2. It returns a boolean value of true only when the expressions on both sides of && are true.Ex:  System.out.println(true && true);

• The second Boolean operator that we will explore is called or.

1. The or operator is represented in Java by ||.2.It returns a Boolean value of true when at least one expression on either side of || is true.Ex: System.out.println(true || false);

• The final Boolean operator we will explore is called not.

1. The not operator is represented in Java by !.

2. 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.

Ex:    System.out.println(!false);
System.out.println( !(5>=1) );

NOTES: The three Boolean operators &&, ||, and ! can also be used together and used multiple times to form larger Boolean expressions,  just like numerical operators, Boolean operators follow rules that specify the order in which they are evaluated. This order is called Boolean operator precedence.

• The precedence of each Boolean operator is as follows:

1.! is evaluated first

2.&& is evaluated second

3.|| is evaluated third

• In Java, the keyword if is the first part of a conditional expression.

1. 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.

Ex: if (9 > 2) {

System.out.println("Control flow rocks!"); }

In the example above, 9 > 2 is the Boolean expression that gets checked. Since the Boolean expression “9 is greater than 2“ is true, Control flow rocks! will be printed to the console.

We could write a second if statement with a Boolean expression that is opposite the first, but Java provides a shortcut called the if/elseconditional.

1. The if/else conditional will run the block of code associated with the if statement if its Boolean expression evaluates to true.

2. Otherwise, if the Boolean expression evaluates to false, it will run the block of code after the else keyword.

For that case, we can use the if/else if/else statement in Java.

1. If the Boolean expression after the if statement evaluates to true, it will run the code block that directly follows.
2. Otherwise, if the Boolean expression after the else if statement evaluates to true, the code block that directly follow will run.
3. Finally, if all previous Boolean expressions evaluate to false, the code within the else block will run.

EX: int shoeSize = 10;

if (shoeSize > 12) { System.out.println("Sorry, your shoe size is currently not in stock."); } else if (shoeSize >= 6) { System.out.println("Your shoe size is in stock!"); } else { System.out.println("Sorry, this store does not carry shoes smaller than a size 6."); }

• The term ternary comes from a Latin word that means “composed of three parts”.

These three parts are:

• 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

We can also set different cases to different answers in the code, this will be really useful for online organizations that wants to do surveys and quizzes.

EX: public class Switch {

public static void main(String[] args) {

char penaltyKick = 'R';

switch (penaltyKick) {

case 'L': System.out.println("Messi shoots to the left and scores!");

break; 

case 'R': System.out.println("Messi shoots to the right and misses the goal!");

break;

case 'C': System.out.println("Messi shoots down the center, but the keeper blocks it!");

break;

default:

System.out.println("Messi is in position...");

}

}

}

What did I learned?

• 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

What I'll be doing tomorrow...

This is the last lesson of Java. For next class, I will go onto w3Schools to do quiz about Java and also Python. Then I will write a review and write down the questions that I got wrong onto the next blog post.