Monthly Archives: October 2014

Student Object (OOP Java)

Student Class

A school district decided to write a program to help keep track of various parts of the school.

It has been decided to store relevant information about Students in a Student class. Each Student will have an array of Strings to store the names of his or her teachers.

private instance variables

 

Part 1

* Construct the Java statement to declare the array called

teachersNames to store the String names of the student’s teachers

Part 2

  • write a default constructor
  • construct a method called  addTeacher( String name) that adds String name to the  teachersNames  array
    • to do this let’s create a private method  private String[] addStr( String[] input, String val) that adds value to the end of the array and returns it. [redact]Solution[/redact]
  • construct hasTeacher(String name)  that returns true if name is in the teachersName array
  • construct a method removeTeacher(String name) that removes the   String name from the  teachersNames  array.
  • construct a method the line of code needed in the setGpa(double to) method of the Student Class.
  • construct a method boolean setTeacher (String name, int index) .   This method should return true if index is valid in the array and false if  index >= teachersName.length

 

Next: The runner class

Playlist Project [Array]

A PlayList project will be based on Three Classes

The Artist class will store core information about an artist

The Song class will store basic information about a music song

The PlayList class will manage lists of songs and artists


 

Artist

  • Constructor(s) :
    public Artist( String name) { //missing code }

 

  • Instance Variables (“global” variables)

 

Methods

 


 

Song

Constructor(s):

Instance Variables

example of how to get current milliseconds as a long

Method

 


 

Artist

Song

PlayList


 

PlayList

  • Instance Variables
    • private String listName : This is the ‘name’ of your playList
    • private Song[] songs;
    • private  int[] stars ; //how many stars each song has between 0 and 5 inclusive.
    • Note: songs and stars are parallel Arrays
  • Constructor
    • public PlayList(String name) : There should be only 1 constructor that takes a parameter representing the name of the playList
  • Accessor Methods
    • public double averageRating() // returns the average star rating for the list
    • public double averageRating(Artist artist)  // returns the mean star rating associated with artist
    • public Song[] getSongs(Artist artist) // returns an array populated by the songs of the parameter artist
    • public Song[] getSongs() // returns all the songs in the list

    Mutator Methods

    • public void swap(Song song1 ,  Song song2 )  // switches positions of these two (maintain parallelism!)
    • public void  add(Song song , int stars)
    • public void removeSong(Song song, String artist )  //removes song associated with artist
      • Note: Be careful here. You are allowed to add the same song and artist. Duplicates are allowed.
    • public void removeArtist(Artist artist ) //removes all elements associated with artist
    • public void removeLowStars(int cutOff) //removes all elements associated with a star rating less than cutOff
    •  ** public PlayList sortByDate() //this returns a rearranged PlayList based on each Song’s date
    • ** public PlayList sortByRating() //this returns a rearranged playlist so that the 5 starred elements are the first group in the list, 4 stars second …1 stars, last
    • ** public PlayList shuffle() //this returns a new PlayList in which all of the songs have been reordered randomly.

Artist

Song

PlayList

Array Fun 2

Array Fun 2

Java Assignment

Create a Class called ArrayFun that has the following methods Write the body for the methods described below.

 

public int[] digitsToArray(int nums)

Description: This method creates an array that is filled with all of the digits of nums.

Method Call return value/output
digitsToArray( 523 ) {5,2,3}
digitsToArray(1267 ) { 1 , 2 , 6 , 7}
public boolean allFactorsOfSum(int[] nums)

Description: This method returns true if each element ofnums is a factor of the sum of nums.

Method Call return value/output
allFactorsOfSum( {6,1,2,3} ) true (because all of the elements are factors of the sum which is12)
allFactorsOfSum( 1,4,7) false (because 7 is not a factor of the sum of this array which is 12)
public String[] doubleArr(String[] strs)

Description: This method returns a new version of strs with each element appearing twice.

Method Call return value/output
doubleArr( {“a”,”b”,”c”} ) {“a”,”a”,”b”,”b”, “c” , “c”}
doubleArr( {“math”,”ware”,”house”,”.com” }) {“math”,”math”,”ware”,”ware”,”house”,”house”,”.com”, “.com”}
public boolean isThere(int[] nums, int num)

Description: This method returns true if num is an element nums.

Method Call return value/output
isThere( {6,1,2,3}, 6) true
isThere( {6,1,2,3}, 5 ) false
public int indexOf(int[] nums, int num)

Description: This method returns the index value of the first appearance of num or -1 if num is not an element of nums .

Method Call return value/output
indexOf( {6,4 ,7,3, 4 }, 4) 1
indexOf( {6,4 7 ,3,2,7}, 7) 2
indexOf( {6,4 ,2,3}, 22) -1
public int lastIndexOf(int[] nums, int num)

Description: This method returns the index value of the last appearance of num or -1 if num is not an element of nums .

Method Call return value/output
lastIndexOf( {6, 4 ,7 ,3, 11, ,4}, 4) 5
lastIndexOf( {7, 6,4 , 7 ,3}, 7) 3
lastIndexOf( {6,4 ,2,3}, 22) -1
public boolean isIncreasing(double[] nums)

Description: This method returns true if each element in nums is greater than the element to its left.

Method Call return value/output
isIncreasing( {1,2,3,4 }) true
isIncreasing( {1,0 ,3,4 }) false
isIncreasing( {1,1, 2,3,4 }) false
public int largestSpan(int[] nums)

Description: This method returns the largest span of consecutive increasing numbers

Method Call return value/output
largestSpan( {4, 3, 1, 2, 3 , 1} ) 3
largestSpan( {4  , 3,  1 , 12 , 31 , 44 , 52 , 1} ) 5
largestSpan( {9, 7, 8 , 12,4, 3, 0, 4 , 1) 3
largestSpan( {1, 0, 4, 5 , 3,  2, 8 , 9, 10, 12, 4, 3,  1 }) 5
** int[] invert(int[] nums)

Description: This method ‘inverts’ an array by spliting the array in halves and ‘inverting’ each half. See sample calls to understand.

Method Call return value/output
invert( {5 , 21, 5, 13,4 }) {4, 13, 5, 21, 5  }
invert( { 1, 2, 3, 4, 5,6  })  { 6, 5, 4, 3, 2, 1}
** int[] shiftByN(int[] nums, int delta)

Description: This method returns the array with all digits shifted by delta . Any digits that are circulated off the end of the array should be returned to the other side. Note: delta could be positive or negative. Please keep in mind that Math.abs(delta) > nums.length could be possible 😉

Method Call return value/output
shiftByN( {5 , 21, 13,4 } 1) { 4 , 5 , 21, 13 }
shiftByN( {5 , 21, 13, 4 , 11} 2) { 4 , 11 , 5 , 21, 13}
shiftByN( {5 , 21, 13, 4 } -1) { 21, 13, 4 , 5}
shiftByN( {5 , 21, 13, 4 ,7 } -2) { 13, 4 ,7 , 5 , 21}
** int[] add(int[] num1, int[] num2, int base) throws ArithmeticException@precondition 1 < base < 11
@precondition num1.length = 5 and num2.length = 5
@postcondition: the returned array has 5 elements representing the sum or an ArithmeticException is thrown

Description: This method attempts to replicate addition. Consider both num1 and num2 represent the five digits of a number. Each element in the array stores one of the digits. For instance, the number 143 would be represented as {0,0,1,4,3 }. Numbers can be in any base between 2 and 10 inclusive , and the number 101102 in binary would appear in an arrays as : {1, 0, 1 , 1, 0 } . Let’s assume the numbers are positive.You should return an array representing the digits of the sum of num1 and num2. If the number of digits in the sum exceeds the maximum number of digits (5) , you should throw an arithmetic exception as shown in the code below:

Note: You may not use any kind of helper or utility methods that are built into pre-defined Java classes for converting numbers between bases. Only use techniques taught in this class.

Method Call return value/output
add( {0,0,0 ,4,2},{0,0,0,5,1}, 10) {0, 0, 0, 9, 3} ie (42 + 51 = 93)
add( {0, 0, 0 ,7,2},{0,0,0,5,1}, 10) {0, 0 , 1 , 2, 3} ie (72 + 51 = 123)
add( {0, 0 , 0 , 1 , 1}, { 0 , 0 , 0 , 1 }, 2) {0, 0 , 1 , 0 , 0} ie ( 112 + 12= 1002 )

Representing Data

Representing Data

You will be responsible for understanding the core concepts behind all the formats/file types (listed in chapter 3 of the book for representing for various types of data (text, images, video), the pros and cons of different formats and when it is appropriate to use different formats. For instance, jpg’s are meant to realistically represent photographs and use color averaging, while GIF’s have a max  of 256 colors and therefore  have much smaller file sizes than jpegs ; the latter are not a good choice for representing photographs but rather for cartoons or line art. Both of these are Raster not vector shapes.

Representing Graphics

Video