Tutorial 3: Operators

Welcome to primary school mathematics again. Back then, we learnt about addition, subtraction, multiplication and division. And these operators are at the core of Java and many other programming languages. 

So why do we need operators? Assume we have declared two integers int j = 8; and int k = 9; Without performing some sort of operation on the integers, they are useless. They don’t tell us much. However, we can add, subtract, multiply or divide the two integers. We can even perform a complex calculation that involves more than one operator on the two integers.

Mathematical Operator	Equivalent Java Operator
+	+
-	-
x	*
÷	/

Table 1: Operators used in mathematics and their Java equivalents.

Now let’s say we want to operations on two values in Java.

For short integers: short m = 2; and short n = 7;

Addition: m + n;

Subtraction: m – n;

Multiplication: m * n;

Division: m / n;

For integers: int i = 5; and int j = 6;

Addition: i + j;

Subtraction: i – j;

Multiplication: i * j;

Division: i / j;

For long integers: long p = 26; and long q = 10;

Addition: p + q;

Subtraction: p – q;

Multiplication: p * q;

Division: p / q;

For floats: float f = 15.5; and float g = 12.6;

Addition: f + g;

Subtraction: f – g;

Multiplication: f * g;

Division: f / g;

For doubles: double d = 14.8; and double s = 12.7;

Addition: d + s;

Subtraction: d – s;

Multiplication: d * s;

Division: d / s;

You remember in elementary school when we were taught about operator precedence? You don’t? Okay. Let me remind you. Say you want to compute 5 + 6 – 3 x 8 / 4. Some operators are given precedence over others. My teacher told me that whenever I have such a problem, I should use the mnemonic BODMAS, which stands for (Brackets Of Division Multiplication Addition and Subtraction). So I would first calculate values in brackets, then do the divisions, then the multiplications, then the addition and finally the subtraction.

There you have it. I’ve just saved you the trouble of looking for your elementary math books :-)

Java also has its own operator precedence rules, such that it will prioritize some operators over others. Understanding and maybe even memorizing these operators can help you make fairly efficient programs. However, if you cannot memorize the operator precedence table, don’t worry, because I also haven’t. A way around this is to use brackets to separate the calculations that you’d like to be done separately.

For example, say I have i x j / k – m + n;

If I would like k – m + n to be computed alone and i x j to be computed alone, I can surround the two fragments with brackets like this: (i x j) / (k – m + n); This ensures that before the division takes place, i x j is computed and k – m + n is computed. 

Boolean Operators

In the last tutorial, we saw that boolean datatypes are either true or false. So, in Java, you can type a statement that Java will check and tell you whether it is true or false. How is this important? Imagine that you want to switch on your TV. What will you do? You will check whether the socket is on. If it is on, you will switch on the TV. If the switch is off, you will have to switch it on before switching on the TV.

So, you will reason like this:

Scenario 1: Is the switch on? Yes…. Then switch on the TV.

Scenario 2: Is the switch off? No…. Then switch on the socket…. Is the switch now on? Yes…. Then switch on the TV.

Operator	Meaning
==	Is equal to
!=	Is not equal to
<	Is less than
>	Is greater than
<=	Is less or equal to
>=	Is more or equal to
!	NOT

Table 2: Boolean operators and their meanings in Java.

In Java, we normally put boolean operators between the items we are comparing. For example: 

1 == 1; is true

1>=5; if false

1<8; is true

However, we normally place the ! operator before the statement in question. For example, we can state that boolean isChecked = true;

If we want to change it to false, we can write !isChecked. This will change isChecked from true to false.

Below is a screenshot of programs that shows operations and the results Java gives. 

Figure 1: Java code showing operations on integers. Answers are displayed on the right. 

It’s very simple. System.out.println() just prints whatever is between the brackets to the console. Notice that with short, int and long, we only get whole numbers as answers even in places where we expect a decimal.

Figure 2: Java code showing operations on float and double. Answers are displayed on the right.

 
Notice now that by using floats and doubles, we get answers with decimals.

Figure 3: Java code showing that you can get different answers by using brackets. Answers are displayed on the right.

Notice that in the first statement, I’ve not used brackets and it gives an answer of 1. In the second statement, I use brackets and it gives an answer of 0.

Figure 4: Java code showing boolean operators. Answers are displayed on the right.

Notice that I have first declared boolean isChecked = false;

 

But in the last statement, I have written !isChecked and what this does is give isChecked a value opposite to what it had. This is why the last statement prints out true instead of false on the console.

Play around with different datatypes and different operators in Java. You’ll love it. And that’s how you learn…by actually doing.

There are other operators known as binary operators, but I’ll cover those in another tutorial. 

Now we know how to declare datatypes, give them values and perform calculations on them. Cool!

As always, you can post a question or comment below and I’ll be more than happy to address it. Until next time, take care.