Introduction to Java programming

learning source

http://www.tutorialspoint.com/java/index.htm

two types of error

compiler-time error: syntax error
run-time error: logic error

algorithms

1. unambiguous
2. executable
3. terminating

methods

1. accessor ( don’t change property)
2. mutator

object

you ask object to do work. you don’t know how they do that
what, not how

comment //

documentation and api

http://docs.oracle.com/javase/7/docs/api/java/lang/String.html

stringObject.replace(char target, char replacement)

import java.awt.Graphics2D;
import java.awt.geom.Rectangle2D;

code mold

public class XX
{
  public static void main(String args[])
  {
    System.out.println();
  }
}

public interface

public void addFriend(Person friend)
public void unFriend(Person nonfriend)
public String getFriend()

Variables

Instance variables (non-static variables)

Class variables( Static variables)

Local variables

example

/**
   A simulated car that consumes gas as it drives.
*/
public class Car
{
    private double milesDriven;
    private double gasInTank;
    private double milesPerGallon;


    /**
       Constructs a car with a given fuel efficiency.
    */
    public Car(double mpg)
    {
        milesDriven = 0;
        gasInTank = 0;
        milesPerGallon = mpg;
    }


    /**
      add gas to the Tank of car
      @param amount the amount of gas added into the Tank
    */

    public void addGas(double amount)
    {
        gasInTank = gasInTank + amount;
    }

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

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

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

public class Friend
  {
  private String name;
  private String friends;
  public void addFriend(Person friend)
  public void unFriend(Person nonfriend)
  public String getFriend()
  }

fundamental data type

overflow

doubles are fuzzy

cast: (int)(3.35)

grayscale: Y=0.2126R+0.7152G+0.0722*B

sunset effect: +25

final int MAX_RED=255;

System.out.printf(“%8.2f\n”, price); // 8 character, 2 decimal points, float type

https://www.udacity.com/wiki/cs046/factsheets?_ga=1.92994461.1633053593.1468204228

import java.util.Scanner;

Scanner in= new Scanner(System.in);

int age= in. nextInt();

java.lang.Math

Math.pow(a, n);

Math.sqrt(100);

Math.max(a,b);

decision

if ()
  {}
else if()
  {}
else
  {}

public static int SECONDS_PER_MINUTE=60;

final int SECONDS_PER_MINUTE=60;

they are never exactly the same

String.equal(); // not ==

final double EPSILON=1e-12;

Math.abs(x-y)<EPSILON; // not ==

loop

for (int i=1;i<=6;i++){} // i is local variable

for (int value:values){} // values is an array

Debugger

1. break point
2. single step
3. inspect variables

ArrayList vs Array

ArrayList values= new ArrayList();

method: get(), set(),add()

double[] values=new double[10];

double[] values={32,54,67.5,29,35};

create a package

Basically, there are two ways:

1. use package statement in the first line in the source file,then
   javac -d . file_name.java
2. use javac -d Destination_folder file_name.java

To use the classes in a package:

import Destination_folder.*

import java.util.

​ Scanner, ArrayList, Arrays, Random

Interface

public interface Drawable
{
  void draw();  // automatically pubic, no implementation
}
public class house implements Drawable

​