JAVAPractical 05 1. Unary operators2. Using Reals3. Conversions4. Type Casting 5. Scope6. Constants

Unary Operators Unary operators such as -- or ++

involve only one variable

For example in order to increase x by 1 the statement x++ is enough

When two variables are used in a calculation it’s called a binary operation

Unary Operators Reminder These only need one variable

1. ++ (increment by 1)2. -- (decrement by 1)3. variable += x (same as variable = variable + x) 4. variable -= x (same as variable = variable - x)5. variable *= x (same as variable = variable * x)6. variable /= x (same as variable = variable / x)7. variable %= x (same as variable = variable % x)

Two ways of Using Unary Operators

Unary operators can be used in two ways;

1. Postfix2. Prefix

Type Statement Equivalent

Postfixn++ n = n +1n-- n = n – 1

Prefix++n n = n + 1--n n =n -1

Example Although the end result is the

same, there is a difference when using postfix or prefix

Output The outputs are the following;

In n++◦ The value of n (9) is stored in x◦ Then n is increased by 1 ◦ Resulting value stored in n

In ++n◦ First n (9) is increased by one ◦ Then the result is stored in x◦ So we end up with the output above

Using RealsWhen numbers with a fraction must

be stored, real type variables must be used;

1. float 2. Double

These can be used just like regular variables

However, when using float the letter f must be added at the end of the number

Example

Conversions When variables are assigned to

other variables for example num1 = num2, one must keep in mind the following:

1. Both variables are of the same data type, or

2. The two variables are compatible,

3. or4. The destination variable type is

larger than the source type.

Examples

byte num2 =13;

short num1 = num2;

This is correct since num1 is short and so it’s a bigger variable type than byte.

long num2;

int num1 = num2;

This is incorrect since we’re trying to fit long data into an int data type and it cannot be done since it’s smaller.

Converting Variable Types We must look at the hierarchy of

variable types in order to know which variables can be converted

Example double is the biggest, so it cannot be converted to anything else; whilst byte (since it’s the smallest) can be converted to any type (except char). Note that boolean data types cannot be converted to anything since they are not numbers

Hierarchy doublefloatlongint

char shortbyte

Type Casting Types can also be changed by

specifying to which type you want to convert them in brackets. For example:

int x = (int) 9.45;This will change 9.45 to an integer (so it

becomes a 9) and stores it in x.

ScopeWhenever the curly brackets are

opened and closed, a scope is created

If a variable is declared in the main scope it can be used throughout the method, however if it is declared between the curly brackets further in the program it will be only available in that scope.

Example

As you can see in the previous example x can be used throughout the program however j can only be used in that scope

Constants A constant is very similar to a variable

The difference is that its values cannot be changed

Hence a constant is read-only

A constant is declared the same as a variable however the keyword final must be used in order to show that it’s a constant

Example For example the mathematical value for PI

never changes,

Hence it can be declared as a constant in our program

In order to identify variables from constants, constants are created using capital letters. 

final double PI = 3.142;