Computer Science - Primitive Types

Common data types

int, double, char, and boolean

Primitive data types

byte, short, int, long, float, double, boolean and char

Non-primitive data types

String, Arrays and Classes

main method

public static void main(String [] args)
-A built-in main method present in every java program
-code inside this method gets executed

Syntax for printing

System.out.print();
System.out.println();

Write the shortest system print method input that would output:
one "two"
three
four"!

System.out.print("one \"two\"\nthree\nfour\"!");

Declaring a variable

Data Type + Variable Name
int age;

lowerCamelCase

A naming convention where the first letter is lower case, and each subsequent start of a word is upper case. Variables must be written in localCamelCase.

Initializing a variable

Data Type + Variable Name + Value
String name = "Naoko"; or name = "Naoko"; if variable has already been declared.

What does the keyword final do?

It prevents variables from being altered.

int number = ((2.0 * 4) / 2) + (3.0 / 2);
number = ?

number = 5;

double number = (2 * 3) / 4;
number = ?

number = 1.0;

double number = (5 % 3) * (5 / 3);
number = ?

number = 2.0;

Add or subtract a variable by 1?

variableName++;
variableName--;

Modify the current value of a variable by another value without calling the variable again.

x += y;
x -= y;
x *= y;
x /= y;
x %= y;

What will the program output?
int num = 2;
int dividend = 5;
dividend /= num;
System.out.println(dividend);

The output will be 2 because when two integers are divided in Java, the decimal portion is always truncated.

Import Scanner

import java.util.Scanner;

Initialize Scanner

Scanner objectName = new Scanner(System.in);

System.in

Value that typically corresponds to keyboard input. including this allows us to input keyboard data into our programs.

Gathering information from user input.

input.nextLine();
input.nextInt();
input.nextDouble();
The data type of the declared variable MUST match the data type of input.next

What happens when nextInt() or nextDouble() comes before nextLine().

nextInt() only reads a portion of the line the user inputs meaning nextLine() will read from the same line as nextInt().

Use nextLine(); after a partial line method.

Add input.nextLine(); after the partial line method.
int number = input.nextInt();
input.nextLine();
String name = input.nextLine();

Casting

Turning one variable type into another.

What happens when we cast a double to an int in the program.

Program will throw an error.

What happens when we cast an int to a double in the program.

Java automatically casts the value correctly.

Fix the code:
int dollars = 100;
int numPeople = 40;
double dollarPerPerson = dollars / numPeople;

int dollars = 100;
int numPeople = 40;
double dollarPerPerson = (double)dollars / numPeople;

Rounding positive and negitive double values with casting.

int positive = (int) (x + 0.5);
int negative = (int) (x - 0.5)

What is the total number of values that int can compute and store.

2^32 different values

What is the range of the total number of values that in can compute and store.

[-2147483648, 2147483647]

Integer.MIN_VALUE - 1

The number will loop back to 2147483647.

Integer.MAX_VALUE + 1

The number will loop back to
-2147483648.