Chapter 4 10/26 & 10/27. More Linux Commands mkdir rmdir echo > redirect output mv file,...

Chapter 4

10/26 & 10/27

More Linux Commands

mkdir rmdir echo > redirect output mv file, directory mv oldFileName newFileName more file rm file

Chapter TopicsConstantsStandard Mathematical MethodsCasting

4.1 Named Constants

ConstantsUnnamed constants

• Literal values – integers, floating-point, boolean

E format may be used for doubles• 1.5e2 --> 150• 8e4 - decimal maybe left off, still a double• 5.1e-4 = ?

Named Constants• Similar to declaring variables, but values can't

be changed.• Use reserved word final• Gives descriptive name, avoids typing

mistakes• All caps by convention

final double TAX = .06;final int DOZEN = 12;final boolean NOT_DONE = false;

Example in Einstein class.

Another Example

• Write a program to input the cost of a car in dollars. Output the sales tax on the car.

• Tax rate is 6% Use a constant.

1.Set taxRate

2.Input cost – use a Scanner

2. Find tax

3. Output tax

.

4.3 Using Math Methods

Standard Mathematical Methods

Java provides a collection of methods to do mathematical tasks•Math is the name of the class•Call to methods is Math.method_name( … )

Examples

Imagine! Java: Programming Concepts in Context by Frank M. Carrano, (c) Pearson Education - Prentice Hall, 2010

Standard Mathematical Methods

Arguments and return type are double:Math.sqrt(x) -- square root of x

Math.pow(x,y) – x to the y power

Math.log(x) – ln x

Math.log10(x) – log10

x

Math.exp(x) – ex

Imagine! Java: Programming Concepts in Context by Frank M. Carrano, (c) Pearson Education - Prentice Hall, 2010

Standard Mathematical Methods

These return same type as argument:Math.abs(x) -- |x|

Math.max(x,y) – maximum of x & y

Math.min(x,y) – minimum of x & y

Math.round(x) – Returns the nearest whole number to x. If x is double it returns a long.

If x is float it returns an int

Imagine! Java: Programming Concepts in Context by Frank M. Carrano, (c) Pearson Education - Prentice Hall, 2010

Standard Mathematical Methods

There more methods, but these are the only ones that will be required for this course.

Imagine! Java: Programming Concepts in Context by Frank M. Carrano, (c) Pearson Education - Prentice Hall, 2010

Standard Mathematical Methods

Call to method Math.sqrt

Imagine! Java: Programming Concepts in Context by Frank M. Carrano, (c) Pearson Education - Prentice Hall, 2010

Example-Quarterback Ages•A QuarterBack class represents a quarterback on a team.

•Write a method to output the difference of this Quarterback's and another one that is passed.

•Output the difference ages as a positive number.

1. diff = | this age – other age|

2. Output diff

Participation

•What is wrong with the following?a.) y = (1/2) * Math.sqrt(x);

b.) y = sqrt(38.0);

c.) y = Math.exp(2,3);

d.) y = math.sqrt( b*b – 4*a*c)/ (2*a);

Participation Example(Skip for now.)

•Write a program to find the 4th root of a number input by the user.•fourthRoot.c

Problem(Skip for now)

Write a program to find the length of side C of a right triangle, given the lengths of sides A and B.

Write the program.

4.4 Type Conversions

11/09/15

Matt Richtel Tonight11/09/15

Tonight at 6 PM in the SUB Jordan Ballroom:

See Matt Richtel who wrote A Deadly Wondering.

Fill out reflection form for 5 extra credit points on homework score.

Or read the book and do a report.

– Report due December 1st.

New Assignments

See the 119 website. Help with: Challenge Activity4.3.2:

Tree Height.

– TreeHeight = ? Let's have a look at Program 6.

Conversion between Numeric Types

Conversion in expressions may happen implicitly or be required explicitly

Consider•Variable is a double.•Literal is an int.•The int is implicitly converted to a double.

Imagine! Java: Programming Concepts in Context by Frank M. Carrano, (c) Pearson Education - Prentice Hall, 2010

Conversion between Numeric Types

However, this does not work in the opposite direction

In expressions•If all values are of same type, result is of that type•If one of the values is a floating-point, the result is floating-point

Imagine! Java: Programming Concepts in Context by Frank M. Carrano, (c) Pearson Education - Prentice Hall, 2010

CastingConversion can be forced with type castingWhat was illegal

Can be made legal

by preceding the desired type in parenthesesThis is considered a unary operator

Imagine! Java: Programming Concepts in Context by Frank M. Carrano, (c) Pearson Education - Prentice Hall, 2010

Program Example

Write a program that asks for the number of cars in a neighborhood and the number of households. It should output the average number of cars per household.

Let's write an algorithm first.

Can use casting to get an accurate double answer.

Questions

What is wrong with this statement? How could it be made legal?

int i = 1.5;

How can I find x2.5 in Java?

Escape sequence Char

\n newline

\t tab

\' single quote

\" double quote

\\ backslash

Using mobaxterm to Transfer Your Program to onyx

•Make a directory on onyx to put you program in

–mkdir myProg4

•Open the directory in the left area of mobaxterm

•Drag the file from the PC’s folder to myProg4 mobaxterm

Java Examples

public class Quarterback{private int age;private int yearPlaying;

//Set the qb's agepublic void setAge(int age){this.age = age;}

//Get the qb's agepublic int getAge(){return age;}

//Set the number of years playingpublic void setYearPlaying(int yearPlaying){this.yearPlaying = yearPlaying;}

//Get the number of years playingpublic int getYearPlaying(){return yearPlaying;}

//Write a method to get the difference between //This Quarterback's age and another one's agepublic int findAgeDifference(Quarterback qb){int diff = Math.abs(this.age - qb.age);return diff;}

}

public class QuarterbackTester{ public static void main(String [] args){

Quarterback rypien = new Quarterback();Quarterback finley = new Quarterback();

rypien.setAge(19);finley.setAge(20);int difference = rypien.findAgeDifference(finley);System.out.println(difference);

}}

import java.util.Scanner;public class Einstein {

public static void main(String[] args) {Scanner kbd = new Scanner(System.in);double e;double m;final double SPEED_OF_LIGHT = 300000000.0;System.out.println("mass?");m = kbd.nextDouble();e = m * SPEED_OF_LIGHT * SPEED_OF_LIGHT;

System.out.println(e + " newtons");kbd.close();

}

}

import java.util.Scanner;import java.text.DecimalFormat;

public class FindTax {

public static void main(String[] args) {//Define a tax rate constantfinal double TAX_RATE = 0.06;//Input priceScanner scan = new Scanner(System.in);System.out.println("Car Price?");double price = scan.nextDouble();

//Figure taxdouble tax = price * TAX_RATE;//Output tax

DecimalFormat formatter = new DecimalFormat("$0.00");

System.out.println("Tax is " + formatter.format(tax));

}

}