COMP-202: Foundations of Programming. Lecture 11: ArrayList, and Linked List Sandeep Manjanna, Summer 2015

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1 COMP-202: Foundations of Programming Lecture 11: ArrayList, and Linked List Sandeep Manjanna, Summer 2015

2 Announcements Assignment 4 will be posted by the end of day today. Course Evaluations are now open. Direct feedback on my course and my teaching. Minerva Student menu t_code=f Final exams : 26 th of June (2pm to MAASS 112

3 This Lecture Review on classes and objects ArrayList Linked List One step at a time.

4 Review: Classes and Objects

5 public class Dog{ private double height; private double age; private static int numdogs = 0; public Dog (double h, double a){ height = h; age = a; numdogs++; System.out.println("The dog's height is "+height+", and age is "+age); public Dog (double a){ age = a; height = 0.5; numdogs++; System.out.println("The dog's age is "+age); public static void main(string[] str){ Dog d1,d2;

6 public class Dog{ private double height; private double age; private static int numdogs = 0; public Dog (double h, double a){ height = h; age = a; numdogs++; System.out.println("The dog's height is "+height+", and age is "+age); public Dog (double a){ age = a; height = 0.5; numdogs++; System.out.println("The dog's age is "+age); public static void main(string[] str){ Dog d1,d2; d1 = new Dog(1.5); d2 = new Dog(1.5, 1);

7 public class Dog{ private double height; private double age; public Dog (double h, double a){ height = h; age = a; public Dog (double a){ age = a; height = 0.5; public boolean equals(dog d){ if((height == d.height) && (age == d.age)) return true; return false; public static void main(string[] str){ Dog d1 = new Dog(1.5); Dog d2 = new Dog(1.5, 1); System.out.println("The two dogs are equal : "+d2.equals(d1));

8 public class Dog{ private double height; private double age; public Dog (double h, double a){ height = h; age = a; public Dog (double a){ age = a; height = 0.5; public boolean equals(dog d){ if((height == d.height) && (age == d.age)) return true; return false; public static void main(string[] str){ Dog d1 = new Dog(1.5); Dog d2 = new Dog(0.5, 1.5); System.out.println("The two dogs are equal : "+d2.equals(d1));

9 public class testdog{ public static void main(string[] str) { Dog d1 = new Dog(1); Dog d2 = new Dog(1.5, 2); swap(d1,d2); System.out.println("d1's age = "+d1.age); public static void swap(dog dog1, Dog dog2) { Dog temp = dog1; dog1 = dog2; dog2 = temp; public class Dog{ public double height; public double age; public Dog (double h, double a){ height = h; age = a; public Dog (double a){ age = a; height = 0.5;

10 public class testdog{ public static void main(string[] str) { Dog d1 = new Dog(1); Dog d2 = new Dog(1.5, 2); swap(d1,d2); System.out.println("d1's age = "+d1.age); public static void swap(dog dog1, Dog dog2) { Dog temp = dog1; dog1 = dog2; dog2 = temp; System.out.println("dog1's age = "+dog1.age); public class Dog{ public double height; public double age; public Dog (double h, double a){ height = h; age = a; public Dog (double a){ age = a; height = 0.5;

11 tostring( ) in objects To be able to print the Objects, you need to implement a method in your class called tostring( ). This helps you print the object just by using the object name as any other primitive type variable. Example: public String tostring() { return "Dog's height = "+height+", and Dog's age = "+age; //in main method: Dog d = new Dog (1.5, 2); System.out.prinln(d); Output: Dog's height = 1.5, and Dog's age = 2.0

12 ArrayList

13 ArrayList Resizeable version of array that includes the useful operations: add, delete, check if value exists, etc.

14 Different Levels of Control Driving a car Do not need to think about how the engine works! If you did, it would be bad. Only have to: hit the gas/brake, turn the wheel at appropriate times. We've abstracted the notion of driving a car.

15 Different Levels of Control Some objects give us more or less control, and be at different levels of abstraction. Car analogy: manual transmission vs. automatic transmission. Trade-off: level of control vs. simplicity to use array higher lower ArrayList lower higher

16 ArrayList Represents the notion of an array, without having to think about the details of how an array works. Must still contain values of the same type!

17 ArrayList of Any Reference Type ArrayList <reference_type_name> (The < > is actually part of the syntax) e.g., ArrayList<String> ArrayList<Scanner> ArrayList<Cat> But not ArrayList<int> ArrayList<boolean>

18 Using an ArrayList An ArrayList is an Object, so you need the new keyword. import java.util.arraylist; ArrayList<String> myarray = new ArrayList<String>();

19 Common Methods til/arraylist.html Notice how the type is referred as E. add(e e) add(int index, E element) clear() get(int index) indexof(object o) remove(object o) remove(int index) size()

20 Example: ArrayList of Names ArrayList<String> names = new ArrayList<String>(); names.add( Jon Stewart ); names.add( Stephen Colbert ); names.add(1, John Oliver ); //now let's print the names: for (int i=0; i < names.size(); i++) { System.out.println(names.get(i));

21 ArrayList of What? In Java, there is a notion of generics. Consider the following two problems: Given a String[] print the elements of the array. Given an int[] print the elements of the array.

22 Printing String[] public static void print(string[] array) { for (int i=0; i < array.length; i++) { System.out.println(array[i]);

23 Printing int[] public static void print (int[] array) { for (int i=0; i < array.length; i++) { System.out.println(array[i]);

24 Only Two Differences Method header is String vs. int In general, basic array operations are the same for any type, except for minor differences.

25 Clever Design of ArrayList Rather than separate types of ArrayLists depending on the type of value being stored, write code that is generic and works on any generic type. We can also define our own classes and methods that make use of generics, but you'll have to take more COMP courses for that.

26 Example: generic ArrayList import java.util.arraylist; public class arraylisttest { public static void main(string[] args) { ArrayList <Dog> dogarr = new ArrayList<Dog>(); ArrayList <String> strarr = new ArrayList<String>(); Dog d = new Dog(1.5); dogarr.add(new Dog(1.5,1)); dogarr.add(new Dog(1.5)); strarr.add("hello"); strarr.add("world"); printarray(dogarr); printarray(strarr); public static void printarray (ArrayList <?> arr) { for(int i=0;i<arr.size();i++) System.out.println(arr.get(i));

27 Try it out!! Write a new version of CatRescue that uses an ArrayList<Cat> instead of Cat[]. Hint: Add a separate int field to keep track of the capacity. This lets you ditch the null checks. Also, add a method, addcapacity(int change) to increase the capacity of the rescue operation by change. We've found more people willing to be foster cat parents.

28 Linked List

29 Data Structures Data structures are a way of organizing collections of data in the computer's memory. Examples of data structures we have seen so far: Arrays :

30 Data Structures Data structures are a way of organizing collections of data in the computer's memory. Examples of data structures we have seen so far: Objects : Point: Cat : //Attributes double age; String name; //Methods public Point(double a, String n)

31 Data Structures Data structures are a way of organizing collections of data in the computer's memory. Examples of data structures we have seen so far: ArrayList :

32 Linked Lists List of Objects linked to each other. Pictorial representation of a Linked list of Cat objects. Cat Cat Cat Cat

33 Linked Lists List of Objects linked to each other. Pictorial representation of a Linked list of Cat objects. Cat Cat Cat Cat

34 Linked Lists List of Objects linked to each other. Pictorial representation of a Linked list of Cat objects. Cat Cat Cat Cat Next Data Next Data Next Data Next Data

35 Linked Lists List of Objects linked to each other. Pictorial representation of a Linked list of Cat objects. Cat Cat Cat Cat Next Data Next Data Next Data Next Data

36 Linked Lists Pictorial representation of a Linked list of Cat objects. Cat Cat Cat Cat Next Data Node Next Data Node Next Data Node Next Data Node InsertEnd( ) InsertStart( ) InsertAt( ) Remove( ) Start Linked List Nothing

37 Linked Lists Pictorial representation of a Linked list of int values. Linked List Start = Data = 3 Data = 2 Data = 5 Data = 1 Data = 7 Next = Next = Next = Next = Next = null Node Node Node Node Node

38 Building our Linked List We need to define a class for each element in the list: the Node class The Node class should have: A pointer to some data. We will call it its data. For simplicity, we will hold int numbers in our LinkedList. A pointer to the next element in the list. Unsurprisingly, we will call it next.

39 Building our Linked List public class Node { private int data; private Node next; // add a constructor here // add getter and setter methods here

40 Building our Linked List We need to define a class for doing operations on the list: the LinkedList class. The LinkedList class should have: A pointer to the first element in the list. We will call it start. All the methods with the operations we want to make on the list.

41 Building our Linked List public class LinkedList { private Node start; // add a constructor here // add Insertion, search and deletion methods here

42 Methods for our Linked List Inserting a node at the beginning of the List. Linked List Start = Data = 9 Next = null new Node Data = 3 Data = 2 Data = 5 Data = 1 Data = 7 Next = Next = Next = Next = Next = null Node Node Node Node Node

43 Methods for our Linked List Inserting a node at the end of the List. Linked List Start = Data = 3 Data = 2 Data = 5 Data = 1 Data = 7 Next = Next = Next = Next = Next = null Node Node Node Node Node Data = 9 Next = null new Node

44 Methods for our Linked List Inserting a node in the middle of the List (Between 5 and 1). Linked List Start = Data = 9 Next = null new Node Data = 3 Data = 2 Data = 5 Data = 1 Data = 7 Next = Next = Next = Next = Next = null Node Node Node Node Node

45 Methods for our Linked List Removing a node from the List (Remove node with Data = 5). Linked List Start = Data = 3 Data = 2 Data = 5 Data = 1 Data = 7 Next = Next = Next = Next = Next = null Node Node Node Node Node

46 Methods for our Linked List Removing a node from the List (Remove node with Data = 5). Linked List Start = Data = 3 Data = 2 Data = 1 Data = 7 Next = Next = Next = Next = null Node Node Node Node

47 Summary Review on Classes and Objects ArrayList Linked List

Garbage Collection (1)

Garbage Collection (1) Coming up: Today: Finish unit 6 (garbage collection) start ArrayList and other library objects Wednesday: Complete ArrayList, basics of error handling Friday complete error handling Next week: Recursion