object arrays. why an array of objects? similar to an array of integers we might want a list of...
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Object Arrays
Why an array of objects?
Similar to an array of integers we might want a list of objects
For example A school has a number of courses
If each course is an object The school can have an array of courses
Review on arrays of primitive types
How to declare (allocate memory) a double array of 10 elements?
Review on arrays of primitive types
How to declare (allocate memory) a double array of 10 elements? double[] rainfall = new double[10];
Review on arrays of primitive types
How to declare (allocate memory) a double array of 10 elements? double[] rainfall = new double[10];
How about a 10 x 20 2D int array?
Review on arrays of primitive types
How to declare (allocate memory) a double array of 10 elements? double[] rainfall = new double[10];
How about a 10 x 20 2D int array? int[][] scores = new int[10][20];
Review on arrays of primitive types
Given the rainfall 1D array, how to find # of elements?
Review on arrays of primitive types
Given the rainfall 1D array, how to find # of elements? rainfall.length
Given the scores 2D array, how to find # of rows and columns?
Review on arrays of primitive types
Given the rainfall 1D array, how to find # of elements? rainfall.length
Given the scores 2D array, how to find # of rows and columns? scores.length scores[0].length
Array of objects
Consider the Person class How to declare an array of 10 Person objects?
Array of objects
Consider the Person class How to declare an array of 10 Person objects? Person[] team = new Person[10];
This is not complete, because ? (a common mistake)
Array of objects
Consider the Person class How to declare an array of 10 Person objects? Person[] team = new Person[10];
This is not complete, because ? (a common mistake) Merely allocate space for the array
Think of it as placeholders for objects We also need to put objects into the array
Similar to populating an int array with desirable values
What to do?
Array of objects
Consider the Person class How to declare an array of 10 Person objects? Person[] team = new Person[10];
This is not complete, because ? (a common mistake) Merely allocate space for the array
Think of it as placeholders for objects We also need to put objects into the array
Similar to populating an int array with desirable values
What to do? team[0] = new Person(“Mary”, 10); team[0] = mary; // mary was created elsewhere
How about a 2D array of objects?
Consider we have 20 basketball teams in a tournament, each has 10 players
How about a 2D array of objects?
Consider we have 20 basketball teams in a tournament, each has 10 players Person[][] basketballTeams = new Person[20][10];
This is not complete, because ?
How about a 2D array of objects?
Consider we have 20 basketball teams in a tournament, each has 10 players Person[][] basketballTeams = new Person[20][10];
This is not complete, because ? basketballTeams [0][0] = new Person(“Mary”, 10);
Given basketballTeams, how to find the number of teams and # of players on each team?
How about a 2D array of objects?
Consider we have 20 basketball teams in a tournament, each has 10 players Person[][] basketballTeams = new Person[20][10];
This is not complete, because ? basketballTeams [0][0] = new Person(“Mary”, 10);
Given basketballTeams, how to find the number of teams and # of players on each team? basketballTeams.length basketballTeams[0].length
Exercise 1
Person class Attributes: name, height (in inches) Constructors:
Person(name, heightInches) Person(name, heightFeet, heighInches)
Methods: getName(), getHeightInches(), getHeightFeetInches()
BasketballTest class Main method:
2D array with 3 teams of 5 players print the tallest player: name and height in feet and inches print the shortest player: name and height in feet and inches print the average height in feet and inches, and the player
closest to the average height
Design
Consider we want to also know their team name, city, and mascot
How would you design the program? Classes:
Design
Consider we want to also know their team name, city, and mascot
How would you design the program? Classes:
Person: Team:
Attributes? Constructors? Methods?
BasketballTest2
Design
Consider we want to also know their team name, city, and mascot
How would you design the program? Classes:
Person: Team:
Attributes: name, city, mascot, roster Constructor: Team(name, city, mascot, roster)
• Why not Team(name, city, mascot, name1, height1, …)? Methods: getName, getCity, getMascot,
getMember(index) BasketballTest2
Exercise 2
Consider we want to also know their team name, city, and mascot
How would you design the program? Classes:
Person: Team:
Attributes: name, city, mascot, roster Constructor: Team(name, city, mascot, roster) Methods: getName, getCity, getMascot,
getMember(index) BasketballTest2
Create an array of 3 teams, each has 5 members Print the tallest, shortest, closest to average height
member and their team name, city, and mascot
Design
Consider Basketball players have jersey numbers Programming contest participants have user names
How would you design the program to allow different types of teams? Classes?
Design
Consider Basketball players have jersey numbers Programming contest participants have user names
How would you design the program to allow different types of teams? Classes:
Person (do we need to change the Person class?) BasketballPlayer (subclass of Person with jersey
number) Programmer (subclass of Person with user name)
Team (do we need to change the Team class?)
Exercise 3
Classes Person
BasketballPlayer (subclass of Person with jersey number) Constructor: BasketballPlayer(name, height, jerseyNumber)
Programmer (subclass of Person with user name) Constructor: Programmer(name, height, username)
Team BasketballProgrammerTest
Create 3 basketball teams, 5 players each Create 3 programming teams, 3 programmers each Find the shortest basketball player and the tallest programmer
print their names, height (feet and inches), jersey/username, and team name