Operators and Operands

An operation is an action performed on one or more values either to modify the value held by one or both of the values, or to produce a new value by combining existing values. Therefore, an operation is performed using at least one symbol and at least one value. The symbol used in an operation is called an operator. A value involved in an operation is called an operand.

A unary operator is an operator that performs its operation on only one operand. An operator is referred to as binary if it operates on two operands.

The semi-colon is used to indicate the end of an expression, a declaration, or a statement. Here are examples:

package Exercise;
import System.*;

As we will learn when studying the for conditional statement, there are other uses of the semi-colon.

Curly brackets are used to create a section of code. As such they are required to delimit the bodies of classes and other statement, such as conditional statements. Curly brackets are also used to create variable scope.

Here is an example:

package Exercise;
import System.*;

public class Exercise
{

}

Like most computer languages, Java uses parentheses to isolate a group of items that must be considered as belonging to one entity. For example, parentheses are used to differentiate a method such as main from a regular variable. Here is an example:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
    }
}

Parentheses can also be used to isolate an operation or an expression with regard to another operation or expression.

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
    }
}

The comma is used to separate variables used in a group. For example, a comma can be used to delimit the names of variables that are declared with the same data type. Here is an example:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
        String firstName, lastName, fullName;
    }
}

The comma can also be used to separate the members the arguments of a method, as we will review them.

1. Start Notepad and type the following:
    

   package GCS; import System.*; public class Exercise { public static void main() { String customerName, homePhone; int numberOfShirts, numberOfPants, numberOfDresses; double priceOneShirt, priceAPairOfPants, priceOneDress; int orderMonth, orderDay, OrderYear; double mondayDiscount; } }

2. Save the file in a new folder named GCS1 inside your JSharp Lessons folder
3. Save the file as Exercise.jsl in the GCS1 folder

The Assignment =

When you declare a variable, a memory space is reserved for it. That memory space is filled with garbage. To "put" a value in the memory space allocated to a variable, you can use the assignment operator represented as =. Based on this, the assignment operation gives a value to a variable. Its formula is:

VariableName = Value

The VariableName factor must be a valid variable name. It cannot be a value such as a number or a (double-quoted) string. Here is an example that assigns a numeric value to a variable:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
        	double salary;

	// Using the assignment operator
	salary = 12.55;
    }
}

Once a variable has been declared and assigned a value, you can call print() or println() to display its value.  Here is an example:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
        double salary;

	// Using the assignment operator
	salary = 12.55;
        Console.Write(salary);
    }
}

This would produce:

12.55

The above code declares a variable before assigning it a value. You will usually perform this assignment when you want to change the value held by a variable. Providing a starting value to a variable when the variable is declared is referred to as initializing the variable. Here is an example:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
        // Initializing a variable
        double salary = 12.55;

        Console.Write(salary);
    }
}

We saw that you could declare various variables at once by using the same data type but separating their names with commas. When doing this, you can also initialize each variable by assigning it the desired value before the comma or the semi-colon. Here is an example:

Practical Learning: Assigning Values to Variables

Single-Quote '

The single quote is used to include one character to initialize, or assign a symbol to, a variable declared as char. A single qoute is usually combined with another single-quote and a character can be included between them. Here is an example:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
        char gender;

        gender = 'M';
        Console.Write(gender);
    }
}

You can include only one character between single-quotes except if the combination of symbols can be evaluated to one character. This is the case for escape sequences. Here is an example:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
        char gender;

        gender = 'M';
        Console.Write(gender);
        Console.Write('\n');
    }
}

The double quote " is used to delimit a string. As mentioned for the single-quote, the double-quote is usually combined with another double quote. Between the combination of double-quotes, you can include an empty space, a character, a word, or a group of words, making it a string. Here is an example:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
        	String message;

	message = "Welcome to the wonderful world of Java";
        	Console.Write(message);
    }
}

A double-quoted string can also be declared and then assigned to a variable.

Practical Learning: Using Quotes

The Positive Operator +

Algebra uses a type of ruler to classify numbers. This ruler has a middle position of zero. The numbers on the left side of the 0 are referred to as negative while the numbers on the right side of the rulers are considered positive:

A value on the right side of 0 is considered positive. To express that a number is positive, you can write a + sign on its left. Examples are +4, +228, +90335. In this case the + symbol is called a unary operator because it acts on only one operand. The positive unary operator, when used, must be positioned on the left side of its operand, never on the right side.

As a mathematical convention, when a value is positive, you don't need to express it with the + operator. Just writing the number without any symbol signifies that the number is positive. Therefore, the numbers +4, +228, and +90335 can be, and are better, expressed as 4, 228, 90335. Because the value doesn't display a sign, it is referred as unsigned.

To express a variable as positive or unsigned, you can just type it. here is an example:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
        	Console.Write("Number = ");
	Console.WriteLine(+802);
    }
}

This would produce:

Number = 802

As you can see on the above ruler, in order to express any number on the left side of 0, it must be appended with a sign, namely the - symbol. Examples are -12, -448, -32706. A value accompanied by - is referred to as negative. The - sign must be typed on the left side of the number it is used to negate. Remember that if a number does not have a sign, it is considered positive. Therefore, whenever a number is negative, it MUST have a - sign. In the same way, if you want to change a value from positive to negative, you can just add a - sign to its left.

Here is an example that uses two variables. One has a positive value while the other has a negative value:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
        	Console.Write("First Number  = ");
	Console.WriteLine(+802);
	// Displaying a negative number
	Console.Write("Second Number = ");
	Console.WriteLine(-802);
    }
}

This would produce:

First Number      = 802
Second Number = -802

Algebraic Operators

In algebra, operations are performed on numeric values. Algebraic operators are represented with the following symbols:

  

The Addition

The addition is an operation used to add things of the same nature one to another, as many as necessary. Sometimes, the items are added one group to another. The concept is still the same, except that this last example is faster. The addition is performed in mathematics using the + sign. The same sign is used in Java.

To get the addition of two values, you add the first one to the other. After the addition of two values has been performed, you get a new value. This means that if you add Value1 to Value2, you would write Value1 + Value2. The result is another value we could call Value3. You can also add more than two values, like a + b + c.

With numbers, the order you use to add two or more values doesn't matter. This means that Value1 + Value2 is the same as Value2 + Value1. In the same way a + b + c is the same as a + c + b the same as b + a + c and the same as c + b + a

Here is an example that adds two numbers:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
        	Console.Write("244 + 835 = ");
	Console.Write(244 + 835);
    }
}

Here is the result:

244 + 835 = 1079

You can also add some values already declared and initialized in your program. You can also get the values from the user.

In Java, you can also add string variables to add a new string. The operation is performed as if you were using numbers. For example, "Pie" + "Chart" would produce "PieChart". You can also add add as many strings as possible by including the + operator between them. Here is an example:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
        String firstName = "Alexander";
	String lastName  = "Kallack";
	String fullName  = firstName + " " + lastName;
	Console.Write("Full Name: " + fullName);
    }
}

This would produce:

Full Name: Alexander Kallack

1. To use the addition, change the file as follows:
    

   package GCS; import System.*; public class Exercise { public static void main() { String customerName = "James Burreck", homePhone = "(202) 301-7030"; int numberOfShirts = 5, numberOfPants = 2, numberOfDresses = 8; double priceOneShirt = 0.95D, priceAPairOfPants = 2.95D, priceOneDress = 3.25D; int totalNumberOfItems; int orderMonth = 3, orderDay = 15, orderYear = 2002; double mondayDiscount = 0.25; // 25% totalNumberOfItems = numberOfShirts + numberOfPants + numberOfDresses; Console.WriteLine("-/- Georgetown Cleaning Services -/-"); Console.WriteLine("========================"); Console.Write("Customer: "); Console.WriteLine(customerName); Console.Write("Home Phone: "); Console.WriteLine(homePhone); Console.Write("Order Date: "); Console.Write(orderMonth); Console.Write('/'); Console.Write(orderDay); Console.Write('/'); Console.WriteLine(orderYear); Console.WriteLine("------------------------"); Console.WriteLine("Item Type Qty Sub-Total"); Console.WriteLine("------------------------"); Console.Write("Shirts "); Console.Write(numberOfShirts); Console.Write(" "); Console.WriteLine(priceOneShirt); Console.Write("Pants "); Console.Write(numberOfPants); Console.Write(" "); Console.WriteLine(priceAPairOfPants); Console.Write("Dresses "); Console.Write(numberOfDresses); Console.Write(" "); Console.WriteLine(priceOneDress); Console.WriteLine("------------------------"); Console.Write("Monday Discount: "); Console.Write(mondayDiscount); Console.WriteLine('%'); Console.Write("Number of Items: "); Console.WriteLine(totalNumberOfItems); Console.WriteLine("========================"); Console.WriteLine(); } }

2. Save the file and switch to the Command Prompt
3. Compile and execute the application. This would produce:
    

   -/- Georgetown Cleaning Services -/- ======================== Customer: James Burreck Home Phone: (202) 301-7030 Order Date: 3/15/2002 ------------------------ Item Type Qty Sub-Total ------------------------ Shirts 5 0.95 Pants 2 2.95 Dresses 8 3.25 ------------------------ Monday Discount: 0.25% Number of Items: 15 ========================

4. Return to Notepad

The multiplication allows adding one value to itself a certain number of times, set by a second value. As an example, instead of adding a value to itself in this manner: A + A + A + A, since the variable a is repeated over and over again, you could simply find out how many times A is added to itself, then multiply a by that number which, is this case, is 4. This would mean adding a to itself 4 times, and you would get the same result.

Just like the addition, the multiplication is associative: a * b * c = c * b * a. When it comes to programming syntax, the rules we learned with the addition operation also apply to the multiplication.

Here is an example:

Practical Learning: Using the Multiplication Operator

The Subtraction

The subtraction operation is used to take out or subtract a value from another value. It is essentially the opposite of the addition. The subtraction is performed with the - sign.

Here is an example:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
        // Values used in this program
	double value1 = 224.58, value2 = 1548.26;
	double result = value1 - value2;

	Console.Write(value1);
	Console.Write(" - ");
	Console.Write(value2);
	Console.Write(" = ");
	Console.Write(result);
    }
}

This would produce:

224.58 - 1548.26 = -1323.68

Unlike the addition, the subtraction is not associative. In other words, a - b - c is not the same as c - b - a. Consider the following program that illustrates this:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
        	// This tests whether the addition is associative
	Console.WriteLine(" =+= Addition =+=");
	Console.Write("128 + 42 +   5 = ");
	Console.WriteLine(128 + 42 + 5);
	Console.Write("  5 + 42 + 128 = ");
	Console.WriteLine(5 + 42 + 128);

	Console.WriteLine();

	// This tests whether the subtraction is associative
	Console.WriteLine(" =-= Subtraction =-=");
	Console.Write("128 - 42 -   5 = ");
	Console.WriteLine(128 - 42 - 5);
	Console.Write("  5 - 42 - 128 = ");
	Console.WriteLine(5 - 42 - 128);
    }
}

This would produce:

=-= Subtraction =-=
128 - 42 -     5 = 81
    5 - 42 - 128 = -165

Notice that both operations of the addition convey the same result. In the subtraction section, the numbers follow the same order but produce different results.

Practical Learning: Using the Subtraction Operator

The Division

Dividing an item means cutting it in pieces or fractions of a set value. For example, when you cut an apple in the middle, you are dividing it in 2 pieces. If you cut each one of the resulting pieces, you will get 4 pieces or fractions. This is considered that you have divided the apple in 4 parts. Therefore, the division is used to get the fraction of one number in terms of another. The division is performed with the forward slash /.

Here is an example:

This would produce:

224.58 / 1548.26 = 0.145053156446592

When performing the division, be aware of its many rules. Never divide by zero (0). Make sure that you know the relationship(s) between the numbers involved in the operation.

Practical Learning: Using the Division Operator

The Remainder

The division program above will give you a result of a number with double values if you type an odd number (like 147), which is fine in some circumstances. Sometimes you will want to get the value remaining after a division renders a natural result. Imagine you have 26 kids at a football (soccer) stadium and they are about to start. You know that you need 11 kids for each team to start. If the game starts with the right amount of players, how many will seat and wait?

The remainder operation is performed with the percent sign (%) which is gotten from pressing Shift + 5.

Here is an example:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
        int Players = 26;

	// When the game starts, how many players will wait?.
	Console.Write("Out of ");
	Console.Write(Players);
	Console.Write(" players, ");
	Console.Write(26 % 11);
	Console.Write(" players will have to wait when the game starts.\n");
    }
}

This would produce:

Java Language Operators

Increment ++

Introduction

We are used to counting numbers such as 1, 2, 3, 4, etc. In reality, when counting such numbers, we are simply adding 1 to a number in order to get the next number in the range. The simplest technique of incrementing a value consists of adding 1 to it. After adding 1, the value or the variable is (permanently) modified and the variable would hold the new value. This is illustrated in the following example:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
        int value = 12;

	Console.WriteLine("Techniques of incrementing a value");
	Console.Write("Value = ");
        	Console.WriteLine(value);

        	value = value + 1;

        	Console.Write("Value = ");
	Console.WriteLine(value);
    }
}

Techniques of incrementing a value
Value = 12
Value = 13

Java provides a special operator that takes care of this operation. The operator is called the increment operator and is represented by ++. Instead of writing value = value + 1, you can write value++ and you would get the same result. The above program can be re-written as follows:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
        int value = 12;

	Console.WriteLine("Techniques of incrementing a value");
	Console.Write("Value = ");
        	Console.WriteLine(value);

        	value++;

        	Console.Write("Value = ");
	Console.WriteLine(value);
    }
}

The ++ is a unary operator because it operates on only one variable. It is used to modify the value of the variable by adding 1 to it. Every time the Value++ is executed, the compiler takes the previous value of the variable, adds 1 to it, and the variable holds the incremented value:

Techniques of incrementing a value
Value = 13
Value = 14
Value = 15

Pre and Post-Increment

When using the ++ operator, the position of the operator with regard to the variable it is modifying can be significant. To increment the value of the variable before re-using it, you should position the operator on the left of the variable:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
        	int value = 12;

	Console.WriteLine("Techniques of incrementing a value");

        	Console.Write("Value = ");
	Console.WriteLine(value);

	Console.Write("Value = ");
	Console.WriteLine(++value);
		
	Console.Write("Value = ");
	Console.WriteLine(value);
    }
}

This would produce:

Techniques of incrementing a value
Value = 12
Value = 13
Value = 13

When writing ++value, the value of the variable is incremented before being called. On the other hand, if you want to first use a variable, then increment it, in other words, if you want to increment the variable after calling it, position the increment operator on the right side of the variable:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
        	int value = 12;

	Console.WriteLine("Techniques of incrementing a value");

	Console.Write("Value = ");
        	Console.WriteLine(value);
        
        	Console.Write("Value = ");
	Console.WriteLine(value++);
		
        	Console.Write("Value = ");
	Console.WriteLine(value);
    }
}

This would produce:

Techniques of incrementing a value
Value = 12
Value = 12
Value = 13

Decrement --

Introduction

When counting numbers backward, such as 8, 7, 6, 5, etc, we are in fact subtracting 1 from a value in order to get the lesser value. This operation is referred to as decrementing a value. This operation works as if a value is decremented by 1, as in value = value – 1:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
        	int value = 12;

	Console.WriteLine("Techniques of decrementing a value");
	Console.Write("Value = ");
	Console.WriteLine(value);

        	value = value - 1;

  	Console.Write("Value = ");
	Console.WriteLine(value);
    }
}

This would produce:

Techniques of decrementing a value
Value = 12
Value = 11

As done to increment, Java provides a quicker way of subtracting 1 from a value. This is done using the decrement operator, that is --. To use the decrement operator, type –- on the left or the right side of the variable when this operation is desired. Using the decrement operator, the above program could be written:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
        int value = 12;

	Console.WriteLine("Techniques of decrementing a value");
	Console.Write("Value = ");
	Console.WriteLine(value);

	value--;

	Console.Write("Value = ");
	Console.WriteLine(value);
    }
}

Pre-Decrement

Once again, the position of the operator can be important. If you want to decrement the variable before calling it, position the decrement operator on the left side of the operand. This is illustrated in the following program:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
        	int value = 12;

	Console.WriteLine("Techniques of decrementing a value");
	Console.Write("Value = ");
	Console.WriteLine(value);

	Console.Write("Value = ");
	Console.WriteLine(--value);
		
	Console.Write("Value = ");
	Console.WriteLine(value);
    }
}

This would produce:

Techniques of decrementing a value
Value = 12
Value = 11
Value = 11

If you plan to decrement a variable only after it has been accessed, position the operator on the right side of the variable. Here is an example:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
        	int value = 12;

	Console.WriteLine("Techniques of decrementing a value");
	Console.Write("Value = ");
	Console.WriteLine(value);

	Console.Write("Value = ");
	Console.WriteLine(value--);
		
	Console.Write("Value = ");
	Console.WriteLine(value);
    }
}

This would produce:

Techniques of decrementing a value
Value = 12
Value = 12
Value = 11

It is not unusual to add or subtract a constant value to or from a variable. All you have to do is to declare another variable that would hold the new value. Here is an example:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
        	double value = 12.75;
	double newValue;

        	Console.WriteLine("Techniques of incrementing and decrementing a value");
	Console.Write("Value = ");
        	Console.WriteLine(value);

        	newValue = value + 2.42;
	
        	Console.Write("Value = ");
	Console.WriteLine(newValue);
    }
}

This would produce:

Techniques of incrementing and decrementing a value
Value = 12.75
Value = 15.17

The above technique requires that you use an extra variable in your application. The advantage is that each value can hold its own value although the value of the second variable depends on whatever would happen to the original or source variable.

Sometimes in your program you will not need to keep the original value of the source variable. You may want to permanently modify the value that a variable is holding. In this case you can perform the addition operation directly on the variable by adding the desired value to the variable. This operation modifies whatever value a variable is holding and does not need an additional variable.

To add a value to a variable and change the value that the variable is holding, you can combine the assignment “=” and the addition “+” operators to produce a new operator as +=

Here is an example:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
        	double value = 12.75;

	Console.WriteLine("Techniques of incrementing and decrementing a value");
	Console.Write("Value = ");
        	Console.WriteLine(value);

        	value += 2.42;
	
        	Console.Write("Value = ");
	Console.WriteLine(value);
    }
}

This program produces the same result as the previous. To decrement the value of a variable, instead of the addition, use the subtraction and apply the same technique. In the above program, the variable can have its value decremented by combining the assignment and the subtraction operations on the variable. This is done with the -= operator. Here is an example:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
        	double value = 12.75;

	Console.WriteLine("Techniques of incrementing and decrementing a value");
	Console.Write("Value = ");
	Console.WriteLine(value);

	value -= 2.42;
		
	Console.Write("Value = ");
	Console.WriteLine(value);
    }
}

This would produce:

Techniques of incrementing and decrementing a value
Value = 12.75
Value = 10.33

Operator Precedence and Direction

When combining operations in Java, there are two aspects involved: an operator's precedence and its direction. If you ask the compiler to add two numbers, for example 240 + 65, it will execute the operation by adding 240 to 65. In other words, it would read 240, then +, then 65, and evaluate the result. This is considered as operating from left to right: 240 -> + -> 65. This process is referred to as the direction of the operation.

As you will regularly combine operators on your various calculations, each operation is known for how much it "weighs" as compared to other operators. This is known as its precedence. This means that when a certain operator is combined with another, such as a + b * c, or x / y - z, some operators would execute before others, almost regardless of how you write the operation. That's why an operator could be categorized by its level of precedence.

One way you can avoid being concerned by the level of precedence of operator is by using parentheses to tell the compiler how to proceed with the operations, that is, what operation should (must) be performed first. Consider the following algebraic operation:

154 - 12 + 8

The question here is to know whether you want to subtract the addition of 12 and 8 from 154 or you want to add the difference between 154 and 12 to 8. Using parentheses, you can communicate your intentions to the compiler. This is illustrated in the following program:

package Exercise;
import System.*;

public class Exercise
{
    public static void main()
    {
        	int operation1 = (154 - 12) + 8;
	int operation2 = 154 - (12 + 8);

	Console.Write("Examining the effect of the parentheses in an operation");
	Console.Write("\n(154 - 12) + 8 = " + operation1);
	Console.Write("\n154 - (12 + 8) = " + operation2);
    }
}

This would produce:

Examining the effect of the parentheses in an operation
(154 - 12) + 8 = 150
154 - (12 + 8) = 134

As you can see, using the parentheses controls how the whole operation would proceed. This difference can be even more accentuated if your operation includes 3 or more operators and 4 or more operands.