Java Data Types

Primitive Data Types

• Java has 8 primitive data types:– char: used to store a single character eg. G– boolean: used to store true or false eg. true– int, byte, short, long: used to store whole numbers

eg. 4– float, double: used to store fractional numbers eg.

7.1

Primitive Data Types

• Pair the following data types to their examples

char int

boolean

float

double

char

boolean

int

827

%

U

9

false

true

2.003.8

Primitive Data Types

• To create and use a primitive data type we need to declare the data type to be used

• We then give it a name• Lastly we give it a value

int age = 17;data type identifier value

• Note: when declaring objects, we use a capital letter for the object typeWhen declaring variables or primitive data types, we use a lower case letter for the data type

Mathematics

• The data types that deal with numbers can be used to calculate the solutions to mathematical equations

• Eg. int result = 6 + 2;• The variable ‘result’ will then contain the

value 8

Mathematics

• We can use the following operands:+ Add- Subtract* Multiply/ Divide% Modulus – remainder after dividing

Mathematics

• Remember that when you do a calculation you must have a variable ready to store the result.

• Complete the following calculations and indicate what would be stored in the variableint resultA = 7 * 2;int resultB = 23%5;int resultC = 16/4;int resultD = resultA + resultC * resultB;

Mathematics

• When I use an int and a float, my answer will be a float.

• If I try to store the answer in the wrong data type I will get an error about “Cannot cast ...”

Type Casting

• We can ‘cast’ data types to change into other data types.

• If I were to cast a float (4.5) to an int, it would truncate all decimals and keep the whole number (4)

• If I were to cast an int (4) to a float, it would add decimals, and since it has no extra information that will be .0 (4.0)

Type Casting

• To cast a data type, you put the type in brackets before the value you want to cast.

• The two examples from the previous slide:4.5 4int solutionA = (int)4.5;4 4.0float solutionB = (float)4;

Type Casting

• In order of operations, e.g. BODMAS, casting is the same as brackets…

• Eg. int result = (int)5.5 * 3;this will truncate 5.5 and leave 5it will calculate 5 * 3it will store the result in the variable ‘result’

• If we wanted to calculate 5.5 * 3 and get an integer result we would have:int result = (int) (5.5 * 3);this calculates 5.5 * 3 (16.5), then truncates the result (16)

Displaying output

• To get your results to appear on the screen, you must use a drawString

• However, if you put the variable name in the quotes, it will simply print out the variable name

• To avoid this you need to concatenate the variable to a string using +

Displaying output

• For example:g.drawString(“The result is: “+result, 20, 20);

• In the brackets of the drawString anything before the first comma is text to be displayed

• But we must make one big string to display by adding (+) all the pieces of information together