Month: January 2017

public class CheckerBoardPainter
{
    /**
     * Spaces are red if one of the coordinates is even and the other is odd
     * Spaces are blue if both coordinates are even
     * Spaces are blue if both coordinates are odd
     * 
     * @return 1 for red spaces and 0 for blue
     * @param row the row of the space to paint
     * @param col the column of the space to paint. 
     */
     public int getColor(int row, int col)
     {
         if (row % 2 == 0 && col % 2 == 0) {
           return 0;
         }  
         else if (row % 2 == 1 && col % 2 == 1) {
           return 0;
         }
         else {
           return 1;
         }
     }
}

西暦が400で割り切れる年はうるう年である
400で割り切れない場合、西暦が100で割り切れる年はうるう年ではない
100で割り切れない場合、西暦が4で割り切れる年はうるう年である
4で割り切れない場合、うるう年ではない

much better to understand
ex if n % 400 != 0 && n % 100 = 0
return うるう年

n = 2000
->　閏年
n = 1900
->　not 閏年
n = 2100
-> not 閏年

1900, 1, 1 Monday
1989, 7, 1
(364 + 365 * 88 + 22 + (31 + 28 + 31 + 30 + 31 + 30 + 1)) % 7 = 5
-> saturday

here is Java code

public class WhatDayWillItBe
{
    public static void main(String[] args)
    {
        Day desiredDay = new Day(1983, 6, 18);

        Day referenceDay = new Day(1900, 1, 1);
        int referenceWeekDay = 1;
        int daysBetween = desiredDay.daysFrom(referenceDay):
        int uncorrectedWeekDay = referenceWeekDay + daysBetween;
        int weekday = uncorrectedWeekDay % 7;

        System.out.print("Weekday: ");
        System.out.println(weekday);
    }
}

largest number of java integer is about two billion. if variable integer over it, it get overflow.

public class MathInJava
{
    public double amdahlSpeedup(double s, double n)
    {
        return 1 / (s + (1 - s)/n);
    }
    public double crossRatio(double a, double b, double c, double d)
    {
        return ((a-c)*(b-d))/((b-c)*(a-d));
    }
    public double average(double a, double b, double c, double d)
    {
        // To do!
        return (a + b + c + d)/ 4.0;
    }
}

    public void reduce()
    {
        red = (red * 6 / 256) * 51;
        green = (green * 6 / 256) * 51;
        blue = (blue * 6 / 256) * 51;
    }

public class PersonDemo 
{
    public static void main(String[] args)
    {
        Person sara = new Person("Sara", "sara.jpg", 10, 200);
        Person chenghan = new Person("Cheng-Han", "cheng-han.png", 300, 0);
        Person cay = new Person("Cay", "cay.gif", 250, 180);
    }
}

// Bluej project: lesson3/friends4
public class Person
{
    private String name;
    private String friends;
    private int x;
    private int y;
    

    public Person (String aName, String pictureName, int xCoord, int yCoord)
    {
        name = aName;
        friends = "";
        x = xCoord;
        y = yCoord;
        Picture picture = new Picture(pictureName);
        picture.translate(xCoord, yCoord);
        picture.draw();
    }
    
    public void addFriend(Person friend) 
    {
        friends = friends + friend.name + " ";
        SmallCircle circle = new SmallCircle(x, y);
        circle.fill();
        Line line = new Line(x, y, friend.x, friend.y);
        line.draw();
    }
    
    public void unfriend(Person nonFriend)
    {
        friends = friends.replace(nonFriend.name + " ", "");
    }
    
    public String getFriends() 
    {
        return friends;
    }
}

The this Reference

public double drive(double distance)
{
  this.mimlesDriven = this.milesDriven + distance
}

public Person (String name, String pictureName, int x, int y)
{
    this.name = name;
    this.friends = "";
    this.x = x;
    this.y = y;
    Picture picture = new Picture(pictureName);
    picture.translate(x, y);
    picture.draw();
}

public class PersonDemo 
{
    public static void main(String[] args)
    {
        Person sara = new Person("Sara", "sara.jpg", 10, 200);
        Person chenghan = new Person("Cheng-Han", "cheng-han.png", 300, 0);
        Person cay = new Person("Cay", "cay.gif", 250, 180);
    }
}

public class Person
{
    private String name;
    private String friends;
    
    public Person (String aName, String pictureName, int xCoord, int yCoord)
    {
        name = aName;
        friends = "";
        Picture picture = new Picture(pictureName);
        picture.translate(xCoord, yCoord);
        picture.draw();
    }
    
    public void addFriend(Person friend) 
    {
        friends = friends + friend.name + " ";
    }
    
    public void unfriend(Person nonFriend)
    {
        friends = friends.replace(nonFriend.name + " ", "");
    }
    
    public String getFriends() 
    {
        return friends;
    }
}

instance variable stay long, but local variable only stay short term.

public class CarTester
{
    public static void main(String[] args)
    {
        Car car = new Car();

        // TODO: Add 20 gallons and drive 100 miles
        car.addGas(20);
        car.drive(100);
        
        // TODO: Print actual and expected gas level
        System.out.println("Expected:18");
        System.out.println(car.getGasInTank());
    }
}

public class Car
{
    private double milesDriven;
    private double gasInTank;
    private double milesPerGallon;

    public Car()
    {
        milesDriven = 0;
        gasInTank = 0;
        milesPerGallon = 50;
    }

    /**
       Drives this car by a given distance.
       @param distance the distance to drive
    */
    public void drive(double distance)
    {
        milesDriven = milesDriven + distance;
        double gasConsumed = distance / milesPerGallon;
        gasInTank = gasInTank - gasConsumed;
    }

    public void addGas(double amount)
    {
        gasInTank = gasInTank + amount;
    }
    
    /**
       Gets the current mileage of this car.
       @return the total number of miles driven
    */
    public double getMilesDriven()
    {
        return milesDriven;
    }

    /**
       Gets the current amount of gas in the tank of this car.
       @return the current gas level
    */
    public double getGasInTank()
    {
        return gasInTank;
    }
}

public class test
{
    public static void main(String[] args)
    {
      Rectangle box = new Rectangle(45, 90, 60, 90);
      box.grow(20, 20);
      system.out.println(box.getX());
      system.out.println("exected: 25");
      system.out.println(box.getY());
      system.out.println("exected: 70");
    }
}

Rectangle frontFace = new Rectangle(20, 30 ,100, 40);
        Line leftLine = new Line(20, 30, 50, 10);
        Line topLine = new Line(50, 10, 150, 10);
        Line middleLine = new Line(120, 30, 150, 10);
        Line rightLine = new Line(150, 10, 150, 50);
        Line bottomLine = new Line(120, 70, 150, 50);

        frontFace.draw();
        leftLine.draw();
        topLine.draw();
        middleLine.draw();
        rightLine.draw();
        bottomLine.draw();

      box.setColor(new Color(255, 0, 0));
      box.draw();
      box2.setColor(new Color(0, 255, 0));
      box2.fill()

java put name before the variable name.

public class test
{
    public static void main(String[] args)
    {
        Picture rocket = new Picture("mariner4.jpg");
        rocket.translate(200, 200);
        rocket.draw();
        Picture planet = new Picture("mars.gif");
        planet.grow(-50, -50);
        planet.draw();
    }
}

public class test
{
    public static void main(String[] args)
    {
        Day birthday = new Day(1951, 5, 26);
        Day lastDay = new Day(2012, 5, 26);
        int daysAlive = lastDay.daysFrom(birthday);
        System.out.println(daysAlive);
    }
}

variable can vary and assignment has no type.

int numberOfPixels = object.methodname(arguments)

public class test
{
    public static void main(String[] args)
    {
        Rectangle box = new Rectangle(60, 90, 20, 30);
        Rectangle box2 = new Rectangle(80, 120, 20, 30);
        box.draw();
        box2.draw();
    }
}

public class test
{
    public static void main(String[] args)
    {
        String river = "Mississippi";
        int numberOfLetters = river.length();
        System.out.println(numberOfLetters);
    }
}

replace method

public class test
{
    public static void main(String[] args)
    {
        String river = "Mississippi";
        String result = river.replaceAll("i","x");
        System.out.println(result);
    }
}

cut space with trim()

String messyString = "Hello, Space!";
        messyString.trim()

AccessorとMutator：「Accessor＝アクセスするヤツ」、「Mutator＝mutate（訳すと変化させる）」
An accessor method is used to return the value of a private field.
A mutator method is used to set a value of a private field. It follows a naming scheme prefixing the word “set” to the start of the method name.

Implement test program, set actual result and expected result.

public class test
{
    public static void main(String[] args)
    {
        System.out.println("Hello\nWorld!");
    }
}

print and println

public class test
{
    public static void main(String[] args)
    {
        System.out.print(3);
        System.out.println(4 + 5);
    }
}

compile error

public class test
{
    public static void main(String[] args)
    {
        System.ouch.println(4 + 5);
    }
}