Primitive data

Week 3

Lecture outcomes

• Primitive data– integer– double– string– char– Float– Long– boolean

• Declaration • Initialisation • Assignments • Arithmetic operators• Boolean operators

Example

• 123 (int)• 1.5 (double)• “HelloWorld” (String)• `H’ (Char)• ….

Data Types

• Constants• Variables

What is a Constant?

• 456—a literal numerical constant– System.out.println(456); // Java– Console.writeline(456); // Visual C#

• “A Literal String Constant”– System.out.println(“My First Java”); // Java– Console.writeline(“My First C#”); // Visual C#

What is a variable?• It is a named computer location in memory

that holds values that might vary• Must that location have an address?– YES

• What has addresses? Bits, bytes, words, what?– Bytes

• Can a variable be more than one byte long?– YES

Data type Declarations

• Specify the type of data and the length of the data item in bytes

• int, short, long• float, double• boolean• char

Data Types -- Integer

• Int – the default declaration – 4-byte integer• Byte—1-byte integer• Short—2-byte integer• Long—8-byte integer

Floating Point

• Float—a 4-byte floating point number• Double—an 8-byte floating point number

There are eight primitive data types

• Boolean, byte, char, int, double, float, long, short

• In bytes, how long is the short data type? The int data type, the long data type?

• In bytes, how long is the float data type? The double data type?

• How long is the char data type?

Primitives sizes and RangesPRIMITIVE SIZE IN BITS RANGE

int 32bits (4 bytes) -231 to 231 -1 -2,147,483,648 to +2,147,483,647

long 64bits -- 8 bytes -263 to 263 - 1

float 32bits- -4 bytes -+(1.40129846432481707e-45 to 3.40282346638528860e+38}

double 64 +-(4.94065645841246544e-324 to 1.79769313486231570e+308)

char 16bits One character

string 16bits per char Not applicable

bool (boolean in Java) 8bits--1-byte True or false

Examples

Type Set of values Sample literal vlues

int interges 99 (-12) 214748647

double Floating-point numbers 3.14 (-1.5) 6.0021 1023

boolean Boolean values True or false

char characters ‘a’ ‘1’ ‘£’ ‘%’ ‘\n’

String Sequence of characters “AC” ”Hello” ” 1.5”

Variable declaration

declaration Variable name Variable type

Int x; x integer

double d; d double

char c; c character

String s; s string

Float f; f float

The assignment operator =

declaration Variable name

Int x;

x = 36;

Declare the variable x as an integer

Sets x to constant 36 at execution time

int x = 36;Sets x = to the constant 36 at compile time

Initializes x to 36 at the time memory is set aside for it

String y;

y = “Hellow”;

Declare the variable x as an integer

Sets y to constant “Hello” at execution time

String y = “Hello”;Sets y = to the constant “Hello” at compile time

Initializes x to “Hello” at the time memory is set aside for it

Initialisation

• If no value is assigned prior to use, then the compiler will give an error

• Java sets primitive variables to zero or false in the case of a boolean variable

• All object references are initially set to null• An array of anything is an object– Set to null on declaration– Elements to zero false or null on creation

Declaration Examples

int index = 1.2; // compiler errorboolean retOk = 1; // compiler errordouble fiveFourths = 5 / 4; // no error!float ratio = 5.8f; // correctdouble fiveFourths = 5.0 / 4.0; // correct

• 1.2f is a float value accurate to 7 decimal places.• 1.2 is a double value accurate to 15 decimal places.

int a, b, c ; b =1; a=b; c =a; System.out.print(“c= “ + c);

• What is the value of a, b & c

Declaration (Cont)

ExampleInt1.java

// uninitialised data// this program will declare and print a numberPublic class int3{ public static void main(String[] arguments) { int weight; System.out.println("your weight is " + weight); }}//end of program

ExampleInt2.java

// this program will declare and print a numberclass int2{ public static void main(String[] arguments) { int weight = 68; System.out.println("your weight is " + weight); }}//end of program

ExampleInt5.java

// uninitialised data// this program will declare and print a numberclass int5{ public static void main(String[] arguments) { int weight;

weight = 65 ; //65 = weight ;

System.out.println("your weight is " + weight); }}//end of program

ExampleString2.java

// this program will declare and print a stringclass string2{ public static void main(String[] arguments) { String name = "Lahcen";

String x = "my name is "; System.out.println( x + name ); //print string x and then string name

}}//end of program

Basic Mathematical Operators

• * / % + - are the mathematical operators• * / % have a higher precedence than + or -double myVal = a + b % d – c * d / b;

• Is the same as:double myVal = (a + (b % d)) –

((c * d) / b);

Basic arithmetic Operators

Operator Meaning E=3 xample

+ Addition 2+3 = 5

* Multiplication 2*3=6

- subtraction 3-2=1

/ division 4/2=2

% mod 5 % 2 = 1, 6 % 2= 0

Precedence Rules

1. Evaluate all sub-expressions in parentheses2. Evaluate nested parentheses from the inside out3. In the absence of parentheses or within

parenthesesa. Evaluate *, /, or % before + or –b. Evaluate sequences of *, /, and % operators from left to

rightc. Evaluate sequences of + and – operators from left to

right

ExampleSumStr.java

public class SumStr

{

public static void main(String args[])

{

System.out.print(args[0] + args[1] );

}

}

}

} 27

Java Argument 2 7

parse a string to integer.SumInt.java

public class SumInt

{

public static void main(String args[])

{

System.out.print( Integer.parseInt(args[0] )+ Integer.parseInt(args[1] ) );

}

}

}

} 9

Java SumInt 2 7

Basic boolean Operators

Operator Meaning E=3 xample

== equal (4-2)==(8-6)

!= Not equal 3 !=2 is true but 4!=(6-2) is false

> Greater than (3>2) is true

>= Greater or equal (3>=2) is true

< Less than (3<2) is false

<= Less or equal (3<=4) is true

Statements & Blocks

• A simple statement is a command terminated by a semi-colon:name = “Fred”;

• A block is a compound statement enclosed in curly brackets:{

name1 = “Fred”; name2 = “Bill”;

}• Blocks may contain other blocks

Flow of Control

• Java executes one statement after the other in the order they are written

• Many Java statements are flow control statements:Alternation: if, if else, switchLooping: for, while, do whileEscapes: break, continue, return

If – The Conditional Statement

• The if statement evaluates an expression and if that evaluation is true then the specified action is taken

if ( x < 10 ) x = 10;

• If the value of x is less than 10, make x equal to 10• It could have been written:

if ( x < 10 )x = 10;

• Or, alternatively:if ( x < 10 ) { x = 10; }

If… else

• The if … else statement evaluates an expression and performs one action if that evaluation is true or a different action if it is false. if (x != oldx) {

System.out.print(“x was changed”);

}

else {

System.out.print(“x is unchanged”);

}

Nested if … else

if ( myVal > 100 ) {if ( remainderOn == true) {

myVal = mVal % 100;}else {

myVal = myVal / 100.0;}

}else{System.out.print(“myVal is in range”);

}

else if

• Useful for choosing between alternatives:if ( n == 1 )

{

// execute code block #1

}

else if ( j == 2 )

{

// execute code block #2

}

else {

// if all previous tests have failed, execute code block #3

}

A Warning…

WRONG!

if( i == j )if ( j == k )

System.out.print(

“i equals k”);

else

System.out.print(

“i is not equal to j”);

CORRECT!

if( i == j ) {

if ( j == k )

System.out.print(

“i equals k”);

}

else

System.out.print(“i is not equal to j”);

// Correct!

The switch Statementswitch ( n ) {case 1:

// execute code block #1break;

case 2:// execute code block #2break;default:// if all previous tests fail

then //execute code block #4

break;}

Summary

• Different data type • Declarations• Arithmetic operators• Parse string to integer.• Boolean operators• Assignments• If statement • Switch statement.

Home work

• Practice with all the exercise on the website • Read chapter 4 on the study guide:– Redo all the examples– Do all the exercises.