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Computational Expression Computer and Java Basics Janyl Jumadinova 16 September, 2019 Janyl Jumadinova Computational Expression 16 September, 2019 1 / 17 Variables Variable is a name for a memorys location where a data value is stored.

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Computational Expression

Computer and Java Basics Janyl Jumadinova 16 September, 2019

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Variables

Variable is a name for a memory’s location where a data value is stored.

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Variables

Variable is a name for a memory’s location where a data value is stored. Variable Declaration allows the compiler to reserve space in the main memory that is large enough for the specified type int count;

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Variables

Variable is a name for a memory’s location where a data value is stored. Variable Declaration allows the compiler to reserve space in the main memory that is large enough for the specified type int count; Variable Assignment assigns a value to the variable count = 0;

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Variables

Variable is a name for a memory’s location where a data value is stored. Variable Declaration allows the compiler to reserve space in the main memory that is large enough for the specified type int count; Variable Assignment assigns a value to the variable count = 0; Must give a value to the variable before using it in the main method.

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Memory Concepts

Variable names correspond to locations in the computer’s memory.

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Memory Concepts

Variable names correspond to locations in the computer’s memory. Every variable has:

a name,
a type,
a size,
a value

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Memory Concepts

Variable names correspond to locations in the computer’s memory. Every variable has:

a name,
a type,
a size,
a value

first = input.nextInt(); stores whatever the user types into the location associated with first.

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Data Types

Data stored in memory is a string of bits (0 or 1)

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Data Types

Data stored in memory is a string of bits (0 or 1) How the computer interprets the string of bits depends on the context. In Java, we must make the context explicit by specifying the type of the data.

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Data Types

Java has two categories of data: primitive data (e.g., number, character)

bject data (programmer created types)

There are 8 primitive data types: byte, short, int, long, float, double, char, boolean Primitive data are only single values; they have no special capabilities.

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Primitive Data Types

integers: byte, short, int, long floating point: float, double characters: char booleans: boolean

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Common Primitive Data Types

Type Description Example of Literals int integers (whole numbers) 42, 60634, -8 double real numbers 0.039, -10.2 char single characters ’a’, ’B’, ’&’, ’6’ boolean logical values true, false

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Range of Values

Type Storage Range of Values int 32 bits

2,147,483,648 to 2,147,483,647

double 64 bits ±10−45 to ±1038 char 16 bits = 2 bytes 0 to 216 or \u0000 to \uFFFF boolean 1 bit NA

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Literal A constant value in Java is created by using a literal representation of it. 100 ( integer literal ) 98.6 ( float literal )

′X ′ ( character literal )

‘‘This is a test’’ ( String literal )

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Constants

Constants hold the same value during their existence. Can use a keyword final before the type and name of the variable:

always contains the same value.

final int MAX BUDGET = 1000

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Expression

Expression is a combination of one or more operators (+, −, %, ...) and

perands (literals, constants, variables,...)

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Order of Precedence

Operators are evaluated in an expression according to the rules of precedence.

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Order of Precedence

Operators are evaluated in an expression according to the rules of precedence. Operators within ( ) are evaluated first. *, /, % evaluated next (L to R). +, - evaluated last (L to R).

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Conversion

Widening

from byte to short, int, long, float or double
from short to int, long, float, double
from char to int, long, float, double
from int to long, float, double
from long to float, double
from float to double

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Conversion

Narrowing - should be avoided!

from byte to char
from short to byte, char
from char to byte, short
from int to byte, short, char
from long to byte, short, char, int
from float to byte, short, char, int, long
from double to byte, short, char, int, long, float

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Conversion

Assignment: grade = ‘A’ Promotion: total/count, where total is a floating point value and count is an integer

Occurs automatically, count is promoted to a floating point value

Casting: grade = (int) total

Java operator: type name in parentheses
Casting converts floating point value total into an integer,

truncating any fractional part.

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Scanner

The Scanner class in the java.util package is a simple text scanner which can parse primitive types and strings. We can use the Scanner class to get the input.

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Scanner

The Scanner class in the java.util package is a simple text scanner which can parse primitive types and strings. We can use the Scanner class to get the input. We must first create an instance of the Scanner as: Scanner name = new Scanner (System.in); to read from the terminal,

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Scanner

The Scanner class in the java.util package is a simple text scanner which can parse primitive types and strings. We can use the Scanner class to get the input. We must first create an instance of the Scanner as: Scanner name = new Scanner (System.in); to read from the terminal,

Scanner name = new Scanner (File filename); to read from the file, where File filename = new File (”input.txt”); and name is the name you choose for your instance of the Scanner

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Scanner Methods

next() : get the next word (token) as a String nextLine() : get a line of input as a String nextInt() : get an integer nextDouble() : get a double value nextFloat() : get a float value

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