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Java
Variables, Types, and Math
Getting Started
Complete and Turn in Address/Poem
Learning Objectives
• Understand how to declare and use
primitives variables.
• Be able to read a simple Java program.
• Be able to incorporate math expressions
into a Java program
• Be able to find and use JavaDocs
Review
• //
• public static void main (String [] args)
• {
–
–
–
–
–
–
–
–
• }
System.out.println(“Hello world”);
System.out.print(“Hello world”);
int num;
num = 30;
double num2;
num = input.nextInt();
double num2 = input.nextDouble();
System.out.printf( “The second number is %5.2f\n", num2 );
Primitive Types (Not objects)
•
•
•
•
•
•
byte
short
int (4 bytes) -2,147,483,648 to 2,1147,483,647
long
+/-9,223,372,036,854,775,808
float
double (8 bytes)
10 e +/-308 with 15 significant digits
• char
• boolean
true or false
public class Interest
{
The variables exist
public static void main(String[] args)
while main is running.
{
/* Declare the variables. */
double principal=0; // The value of the investment.
double rate, interest; // The annual interest rate.
// Interest earned in one year.
/* Do the computations. */
principal = 17000;
rate = 0.07;
interest = principal * rate; // Compute the interest.
principal = principal + interest;
// Compute value of investment after one year, with interest.
// (Note: The new value replaces the old value of principal.)
/* Output the results. */
System.out.print("The interest earned is $");
System.out.println(interest);
// Can also use
//System.out.print("The interest earned is $“ + interest);
System.out.print("The value of the investment after one year is $");
System.out.println(principal);
} // end of main()
} // end of class Interest
Sort of primitive type, but it’s an
object
• String
A sequence of characters.
– The type declarations does start with an
uppercase letter.
Variables in Programs
• Declare the variables inside the main
subroutine. (For now)
• You can also declare variables where you
need them. (Declare a looping variable at
the loop)
– int numberOfStudents;
– String name;
– double x,y;
– boolean isFinished;
import java.util.Scanner; // program uses class Scanner
public class Addition
{
// main method begins execution of Java application
public static void main( String args[] )
{
// create Scanner to obtain input from command window
Scanner input = new Scanner( System.in );
int number1; // first number to add
int number2, sum; // second number to add
String name;
System.out.print( "Enter first integer: " ); // prompt
number1 = input.nextInt(); // read first number from user
System.out.print( "Enter second integer: " ); // prompt
number2 = input.nextInt(); // read second number from user
Simple
input and
math
Use
input.nextDouble();
for getting a double
value
System.out.print("Enter your name ");
name = input.nextLine();
sum = number1 + number2; // add numbers
System.out.printf( "Sum is %d\n", sum ); // display sum
System.out.println("Thanks " + name);// Note: Uses the + for concatenating
} // end method main
} // end class Addition
// Addition.java
// Addition program that displays the sum of two
numbers.
• Displays the file name and a brief
description of the program
import java.util.Scanner;
•
•
•
•
Import declaration
This is a predefined class this program will use
Package: A collection of classes.
Java Class Library or Java Application Programming
Interface (API): Collection of Packages
• This will use the Scanner class from the java.util
package
• Note: All import declarations MUST appear before the
first class declaration in the file. Placing an import
declaration inside a class declaration’s body or after a
class declaration is a syntax error.
• Note: “cannot resolve symbol” error->Forgetting to
include an import declaration for a class used in your
program.
public class Addition
• Begins the declaration of the Addition
class.
• The file name must be Addition.java (case
sensitive)
Scanner input = new Scanner( System.in );
• Variable declaration
• Declares the variable (object) input is of type
Scanner.
• Scanner enables the program to read data
(numbers) for use in the program.
• = Declares that the Scanner variable input
should be initialized in its declaration with the
result of the expression newScanner(System.in)
to the right side of the =.
• Creates a Scanner Object that can be used to
read data entered through the keyboard.
int number1; // first number to add
int number2; // second number to add
int sum; // sum of number1 and number2
• Declares three integer variables.
• -2,147,483,648 to 2, 147, 483, 647
• Other types
– float like real numbers
– char: characters
• Primitive or built in types
• Variables follow identifier rules
– Start the variables with a lowercase letter. (Style)
System.out.print( "Enter first integer: " );
• The prompt for user input
• Need to include a prompt for every value
input
number1 = input.nextInt();
• Uses the Scanner object input.nextInt()
method to obtain an integer from the user
at the keyboard. At this point the program
waits for the user to type the number and
press enter.
• This line is read “number1 is assigned the
value of input.nextInt().”
Other common Scanner
Methods for input
• Entering an Integer
– integerVariable = input.nextInt();
• Entering a double
– doubleNumber = input.nextDouble();
• Entering a String. Reads the entire line.
– stringVariable = input.nextLine();
• Entering a String. Reads until it gets to a
space
– stringVariable = input.next();
sum = number1 + number2;
• Calculates the sum of number1 and
number2 and places the result in the
integer variable sum.
System.out.printf( "Sum is %d\n", sum );
• Displays the sum.
• Could also use
•
•
•
•
•
System.out.printf( "Sum is %d\n", number1+number2 );
Or
System.out.println(“Sum is “ + sum);
But this will give a result you might not expect.
System.out.println(“Sum is “ + number1 + number2);
Simple Integer Math Operations
()
• * Multiply
• / Integer Division
• % MOD, The remainder of integer division.
• +, • Order of Operation
– ()
– *, /, %
– +, -
Evaluate the following
1.
2.
3.
4.
5.
6.
7.
8.
5/2
24 / 15
15 / 24
5%2
24 % 15
17 % 12
140 / 25
140 % 25
Show javadocs
• On the left lists the different classes.
• Use the button on the class website to get to
Javadocs
• Find the Math class and look up the following
methods.
– PI
– sqrt
– pow
• To use these in a program you need to use the form
• ClassName.methodName(arguments if any)
• Math.method(arguments)
Examples
1.
2.
3.
4.
ans = Math.sqrt(9);
ans = Math.sqrt(16);
ans = Math.pow(3);
ans = Math.sqrt(Math.pow(3,2) + Math.pow(2,2));
Translate to Java
Math
2(a+c)
3x + 5y
(1/2)bh
πr2
a 2  b2
2 x 3 y
5a  c
 b  b 2  4ac
2a
Java
Ans=2*(a+c);
public class DryRun9_15_09
{
public static void main(String[] args)
{
Dry Run the Following
int a, b, c = 20;
double d = 1.0;
a = c + 10;
b = a + c;
System.out.println("Numbers " + a +" " + b + " " + c);
System.out.println(a+b+c);
c = a % 7;
b = a / 7;
a = a + 2*b + c % 3;
System.out.println("Numbers " + a +" " + b + " " + c);
System.out.println(a+b+c);
d = 1.0/3;
System.out.println(d);
System.out.printf("%5.2f \n", d);
d = Math.sqrt(a-b);
System.out.println(d);
System.out.printf("%5.2f \n", d);
}
}
First Input Programs
• Mile to inch: YourNameMileToInch
– Input: The number of miles traveled
– Output: The equivalent distance converted to inches
– 5280 feet per mile, 12 inches per foot
• Change: YourNameChange
– Input: The amount of change in pennies
– Output: The least amount of coins it takes to make the change.
–
Example: Input: 66 cents
»
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»
»
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Output:
To get 66 cents you need:
2 Quarters
1 Dime(s)
1 Nickel(s)
1 Cent(s)
Second Input Program
• Complete one of the following
– Quadratic formula
Complete additional
programs as pushes.
• Input: a, b and c (of type double)
• Output: The positive root (-b + sqrt(b2 – 4ac))/(2a)
– Distance formula
• Input: The x and y coordinates for two points
• Output the distance between the points:
– Distance = sqrt((y1-y2)2 + (x1-x2)2)
• Push: Calculate the distance between two points that are on a
3-D grid. That is they have an x, y, and z value.
– Given the lengths of three sides of a triangle, find the
area of the triangle.
• Find a way to calculate this even if it is not a right triangle. (Do
a little research)