Hello everyone, welcome to the third lesson in my Java programming for beginners tutorials series. The second lesson(lesson - 1) - Variables can be found at - https://steemit.com/programming/@robertlyon/java-programming-for-beginners-lesson-1-variables

In this lesson, I am going to be focusing on operators and conditional statements. We are going to look at mathematical operators first. Then we will take a look at relational and logical operators which will set us up for covering If statements in the next lesson.

Operators

So operators are ways of manipulating our data, you will be familiar with basic math operators such as + and - which I will cover in this section. These operators allow us to perform actions on our variable and create our logic. In this section, I will cover all the basic operators that you need for working with Java.

Unary Operators

Below is a list of the unary operators.

Prefix	Postfix
++num	num++
--num	num--

In this table num represents a variable that will hold a value.

Unary operators are operators that are performed on just 1 operand. If we consider the statement 1 + 2. This statement has 2 operands the number 1 on the left-hand side and the number 2 on the right-hand side. In contrast, unary operators only have the one operand an example of this in Java is.

postfix

In this program i++ can be thought of as i = i + 1;

int i = 1;
System.out.println(i++);

The output of this program will be 1 as can be seen in the image below.

note the output of 1.

Now you may be thinking if i = 1 + 1. Then why is the output not 2. this is because i++ is a postfix operator, that means the ++ part is evaluated last. So after the value of i is printed to the screen. The variable i is incremented by 1. See the code and image below.

int i = 1;
System.out.println(i++);
System.out.println(i);

As can be seen in the output above, the second println statement produced the value 2. This shows that the variable i was indeed incremented in the line above.

prefix

Now if we wanted the first println statement to print ou the value 2 we could have used the prefix operator++i. This operator increments the variable by 1 before it gets printed out. See below for an example of this.

int i = 1;
System.out.println(++i);

As can be seen above the output for this program is indeed 2.

The use of the unary operators will become more clear when we cover loops.

Arithmetic

Arithmetic operators are operators that allow us to perform mathematical calculations within our program. You should be familiar with these basic operators as most of them are covered in elementary mathematics. See the table below for a list of these operators.

Operator	Description	Example
+	Addition operator	1 + 1 = 2
-	Subtraction operator	1 - 1 = 0
*	Multiplication operator	6 * 2 = 12
/	Division operator	6 / 2 = 3
%	Modulo/ remainder	6 % 4 = 2

The only operator here you are likely to not have seen before is the modulo operator which simply returns the remainder of the sum.

Lets look at some examples of code before we move onto creating a simple calculator.

Try to guess what the output of each of these calculations will be.

int num1 = 1;
int num2 = 2;

System.out.println(num1 + num2); 
System.out.println(num2 - num1); 
System.out.println(num2 * num2); 
System.out.println(num2 / num1);
System.out.println(15 % num 2);

//A few more difficult ones

System.out.println((num1 * num2) + num1);
System.out.println((num2 * num2) % num2);

Answers can be seen above.

Note my use of parentheses on the last two examples. Operators in Java follow the same precedence rules as they do in real-world mathematics.

Relational Operators

Relational operators help us to check the relationship between two pieces of data. See below for a list of the relational operators.

Operator	Description	Example
<	Less than	1 > 1 = false
>	Greater than	2 > 1 = true
<=	Less than or equal to	6 <= 6 = true
>=	Greater than or equal to	1 >= 17 = false
==	Equal to	6 == 6 = true
!=	Not equal to	5 != 89 = true

These operators should be familiar to you and are covered in elementary mathematics. The output from using these operators is a boolean so it will always output a true or false value.

Lets have a look at these operators in code. As I will be covering the use of these operators in more depth in the next lesson I am not going to go too much into depth here, they are pretty self-explanatory anyway.

Try to guess the output of each line, answers will be provided below. Remember that the output will either be true or false.

System.out.println(1 < 2);
System.out.println(67 > 890 );
System.out.println(56 >= 56);
System.out.println(61 <= 900);
System.out.println(55 == 155);
System.out.println(100 != 34);

The answers above show that the output from using these operators is a true or false value. The usefulness of these operators will become more apparent when we cover if statements and later loops.

Logical Operators

The last set of operators that I wish to cover are logical operators. These operators are usually paired up with rational operators to provide conditional statements. The use of which will become apparent in the next lesson "If statements".
See the table below for a list of Logical Operators

Operator	Description
&&	AND
	OR
!	NOT

Apologies for the OR statement markdown does not provide an escape character for the pipe character.
The OR operator is a double pipe ||.

The AND operator returns true if the statements on both sides of the operator evaluate to true.
The OR operator returns true if the statements on either side of the operator are true.
The NOT operator returns the opposite from what the statement returns.

Here are some examples below. These examples include the rational statements from the section before. Try and work out what the output of these statements could be. I have given the answer for the first 2. Pay close attention to number 3.

System.out.println(1 < 2 && 1 == 1); //true
System.out.println(67 > 890 || 6 != 6 ); //false
System.out.println(!(56 >= 56));
System.out.println(61 <= 900 || 6 == 6);
System.out.println(55 == 155) && 77 > 3;
System.out.println(100 != 34 || 7 > 3);

Challenge

To finish off with I would like you to create some of your own statements like the ones we created in the last section. The more practice you get with these logical expressions the more familiar you will become with them.

Conclusion

In this lesson we covered almost all of the basic operators that are needed to write basic java programs, there are a few that I have deliberately missed and will come back and touch on them at a later date.

If there is anything in this lesson that confuses you or there is anything programming related that you need help with then please comment below and I will try my best to help you.

As always if there are any improvements you think I can make to this post then please leave a comment and I will consider adding it.

The next lesson that I plan to do will be covering If statements and user input. This will allow us to interact with the program and let the computer make decisions based on our input.

Thank you for reading and I hope that someone will get some use out of these tutorials.

Message to readers
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