Computer Programming Chapter 6 : Array and ArrayList

Computer Programming
Chapter 6 : Array and ArrayList

Atit Patumvan
Faculty of Management and Information Sciences
Naresuna University

Tuesday, August 2, 2011

2

Collections

• Collection is a group of objects contained in a single
element.

• Example of collection include an array of integer, a vector
of string, or a hash map of vehicles.

• The Java Collection Framework is a uniﬁed set of classes
and interfaces deﬁned in the java.util package for storing
collections.

Atit Patumvan, Faculty of Management and Information Sciences, Naresuan University

3

อาเรย์ (Array)

• เป็นโครงสร้างพื้นฐานในการจัดเก็บชุดข้อมูล

• เป็นการจัดเก็บชุดข้อมูลที่มีชนิดเดียวกันเข้าไว้ด้วยกัน

• ข้อมูลแต่ละตัวเรียกว่า อิลิเมนต์ (element) หรือ เซลล์ (cell)

• การอ้างอิงถึงข้อมูลที่อยู่ในแต่ละอิลิเมนต์ จะใช้ตัวชี้ที่เรียกว่า อิน
เด็กซ์ (index) หรือ ซับสคริปต์ (subscript)

• การอ้างอิงถึงข้อมูลจะต้องอยู่ใน เครื่องหมาย bracket ʻ[ ]ʼ


4

อาร์เรย์ (Array)

01: public class PoorScoreProcessing {
02:
03: public static void main(String[] args) {
alice_score 04: int alice_score = 18;
05: int bob_score = 20;
18 06: int carry_score = 35;
07: int dart_score = 21;
int 08: double average_score = averageScore(
bob_score
09: alice_score,
20 10: bob_score,
11: carry_score,
int 12: dart_score);
carry_score 13: System.out.println("Average score is " + average_score);
14: }
35 15:
16: public static double averageScore(
int 17: int s1,
dart_score 18: int s2,
19: int s3,
21 20: int s4) {
21: int sum = s1 + s2 + s3 + s4;
int 22: double avr = sum / 4.0;
23: return avr;
24:
25: }
26: }

5

อาร์เรย์ (Array)

score int

18 20 35 21

01: public class ScoreProcessing {
02:
04: int[] score = {18, 20, 35, 21};
05:
06: double average_score = averageScore(score);
07: System.out.println("Average score is " + average_score);
08: }
09:
10: public static double averageScore(int[] scores) {
11: int sum = 0;
12: for (int score : scores) {
13: sum += score;
14: }
15: double avr = sum / (double) scores.length;
16: return avr;
17:
18: }
19: }

6

การประกาศอาเรย์ (Array Declaration)

Name of array variable length

double [] data = new double [10];

type of array variable element type

data

double double double double double double double double double double

double [ ]
data @AB1F245H
double[ ]

double[ ]@AB1F245H

double double double double double double double double double double


7

การประกาศอาเรย์ (Array Declaration)

int [ ] numbers = new int [10]

final int LENGTH = 10;
int [ ] numbers = new int [ LENGTH ];
int length = in.nextInt();
int [ ] numbers = new int [ length ];

int [ ] numbers = { 0, 1, 4, 9, 16};

String [ ] friends = {“Alice”, “Bob”, “Carry”};

Person alice = new Person();
Person bob = new Person();
Person carry = new Person();
Person [ ] persons = {alice, bob, carry};


8

Array Reference

01: public class ArrayReference {
02:
04: int[] array1 = {1, 2, 3, 4, 5};
05: int[] array2 = array1;
06: array1[0] = 7;
07: System.out.println(array2[0]);
08: }
09: }

int[ ]@AB1F245H
array1 @AB1F245H
int[ ] 1 2 3 4 5
int[0] int[1] int[2] int[3] int[4]
array2 @AB1F245H
int[ ]


9

ข้อผิดพลาดที่เกิดขึ้นเป็นประจํา (Common Errors)

• อ้างอิงอินเด็กซ์ผิดพลาด (Bound Error)
01: public class ArrayError1 {
02:
04: int[ ] data = new int[10];
05: data[10] = 5.4; // Error: data has 10 elements with index value 0 to 9
06: }
07:}

• ไม่ได้จองพื้นที่ในหน่วยความจํา (Initialized Error)
01: public class ArrayError2 {
02:
04: int[ ] data;
05: data[0] = 5.4; // Error: data not initialized
06: }
07:}


10

การเติมสมาชิก (ﬁlling)

01: public class FillingArray {
02:
04: int[] data = new int[5];
05: for (int index = 0; index < data.length; index++) {
06: data[index] = index * index;
07: }
08: }
09:}

0 1 4 9 16
data
int[0] int[1] int[2] int[3] int[4]


11

การหาผลรวมและค่าเฉลี่ย (sum and average)

0 1 4 9 16
data
01: public class SumAndAverage { int[0] int[1] int[2] int[3] int[4]
02:
06: data[index] = index * index;
07: }
08:
09: double total = 0;
10: for (int element : data) {
11: total = total + element;
12: }
13: double average = 0;
14: if (data.length > 0) {
15: average = total / (double) data.length;
16: }
17: System.out.println("total: " + total);
18: System.out.println("average: " + average);
19: }
20:}


12

หาค่ามากและหาค่าน้อย (maximum and minimum)

01: public class MinMax {
02:
06: data[index] = (int) (Math.random()*100);
07: System.out.println("data["+index+"]="+data[index]);
08: }
09:
10: int min = data[0];
11: int max = data[0];
13:
14: if(min > data[index]){
15: min = data[index]; data[0]=16
16: } data[1]=37
17: data[2]=11
18: if(max < data[index]){
data[3]=32
19: max = data[index];
20: } data[4]=92
21: } min: 11
22: max: 92
23: System.out.println("min: " + min);
24: System.out.println("max: " + max);
25: }
26:}

13

หาค่ามากและหาค่าน้อย (maximum and minimum)

01: public class MinMax {
02:
06: data[index] = (int) (Math.random()*100);
07: System.out.println("data["+index+"]="+data[index]);
08: }
09:
10: int min = data[0];
11: int max = data[0];
13:
14: if(min > data[index]){ data[0]=16
15: min = data[index];
16: }
data[1]=37
17: data[2]=11
18: if(max < data[index]){ data[3]=32
19: max = data[index]; data[4]=92
20: }
21: } min: 11
22: max: 92
23: System.out.println("min: " + min);
24: System.out.println("max: " + max);
25: }
26:}

14

ค้นหาสมาชิกของอาเรย์ (Search)

01: public class Search {
02:
04: int[] data = new int[5]; data[0]=7
06: data[index] = (int) (Math.random()*10); data[1]=4
07: System.out.println("data["+index+"]="+data[index]); data[2]=3
08: } data[3]=6
09: int searchValue = 5;
10: int position = 0;
data[4]=2
11: boolean found = false; search value = 5
12: while(position < data.length && !found){ Not found
13: if(data[position]== searchValue){
14: found = true;
15: } else { data[0]=1
16: position++;
data[1]=3
17: }
18: } data[2]=5
19: System.out.println("search value = " + searchValue); data[3]=8
20: if(found){ data[4]=4
21: System.out.println("Found at "+position );
22: } else {
search value = 5
23: System.out.println("Not found"); Found at 2
24: }
25: }
26:}

15

Insert an Element

01: import java.util.Arrays;
02:
03: public class ArrayInsertElement {
04:
05: public static void insertElement(int[] data, int index, int value) {
06:
07: for (int position = data.length - 2; position >= index; position--) {
08: data[position + 1] = data[position];
09: }
10: data[index] = value;
11: }
12:
16: data[index] = (int) (Math.random() * 10);
17: System.out.println("data[" + index + "]=" + data[index]);
18: }
19: data[0]=7
20: System.out.println("Before :" + Arrays.toString(data)); data[1]=3
21: insertElement(data, 1, 99); data[2]=9
22: System.out.println("After :" + Arrays.toString(data)); data[3]=0
23: } data[4]=2
Before :[7, 3, 9, 0, 2]
24: }
After :[7, 99, 3, 9, 0]

16

Copy Array

01: import java.util.Arrays;
02:
03: public class ArrayCopy {
04:
06: int[] data1 = new int[5];
07: for (int index = 0; index < data1.length; index++) {
08: data1[index] = (int) (Math.random() * 10);
09: System.out.println("data[" + index + "]=" + data1[index]);
10: }
11:
12: System.out.println("data1[] =" + Arrays.toString(data1));
13: int[] data2 = Arrays.copyOf(data1, data1.length);
14: System.out.println("data2[] =" + Arrays.toString(data2));
15: }
16: }
data[0]=9
data[1]=2
data[2]=6
data[3]=7
data[4]=3
data1[] =[9, 2, 6, 7, 3]
data2[] =[9, 2, 6, 7, 3]

17

Two Dimensional Arrays

Winter Olympics 206: Figure Skating Medal Counts
0 0 1
Gold Silver Bronze counts

Canada 0 0 1 0 1 1
China 0 1 1
Japan 1 0 0
1 0 0
Russia 3 0 0 3 0 0
number of rows
Name of array variable int [ ] [ ] counts = {
{0,0,1},
{0,1,1},
{1,0,0},
int [ ][ ] data = new int [4][3]; {3,0,0}
};
type of array variable number of columns

element type


18

Accessing Two-Dimensional Arrays

01: public class MultiDimensionalArrays {
02:
03: public static final int COUNTRIES = 4;
04: public static final int MEDALS = 3;
05: 0 0 1
06: public static void main(String[] args) { 0 1 1
07: int[][] counts = {
08: {0, 0, 1},
1 0 0
09: {0, 1, 1}, 3 0 0
10: {1, 0, 0},
11: {3, 0, 0}
12: };
13: for (int i = 0; i < COUNTRIES; i++) {
14: for (int j = 0; j < MEDALS; j++) {
15: System.out.printf("%8d", counts[i][j]);
16: }
17: System.out.println();
18: }
19: }
20: }


19

Using Objects in Arrays

01: import java.util.Arrays; 01: public class ModalCount {
02: 02:
03: public class Country { 03: public static void main(String[] args) {
04: public static final int GOLD = 0; 04: Country[] countries = new Country[4];
05: public static final int SILVER = 0; 05: countries[0] = new Country("Canada");
06: public static final int BRONZE = 0; 06: countries[1] = new Country("China");
07: 07: countries[2] = new Country("Japan");
08: private String name; 08: countries[3] = new Country("Russia");
09: private int [] counts = new int [3]; 09:
10: 10: countries[0].setModal(Country.BRONZE, 1);
11: public Country(String name){ 11: countries[1].setModal(Country.SILVER, 1);
12: this.name = name; 12: countries[1].setModal(Country.BRONZE, 1);
13: } 13: countries[2].setModal(Country.GOLD, 1);
14: 14: countries[3].setModal(Country.GOLD, 3);
15: public void setModal(int type, int number){ 15:
16: counts[type]=number; 16: System.out.println(countries[0]);
17: } 17: System.out.println(countries[1]);
18: 18: System.out.println(countries[2]);
19: @Override 19: System.out.println(countries[3]);
20: public String toString(){ 20: }
21: return name +"="+ Arrays.toString(counts); 21: }
22: }
23: }


20

ArrayList

• ArrayList is a class in the standard Java libraries

• ArrayList is an object that can grow and shrink while your
program is running

• An ArrayList serves the same purpose as an array, except
that an ArrayList can change length while the program is
running


21

Declaring and Using Array List

Name of number of rows
array list variable

ArrayList <String> friends = new ArrayList<String>();

type of element type
array list variable

friends.add(“Alice”);
String name = friends.get(i);
friends.set(i, “Bob”);


22

Working with Array List

01: import java.util.ArrayList;
02:
+ Person 03: public class AddingElements {
04:
- name : String 05: public static void main(String[] args) {
06: ArrayList<Person> friends = new ArrayList<Person>();
07: friends.add(new Person("Alice"));
+ Person(String) 08: friends.add(new Person("Bob"));
+ getName() : String 09:
+ setName(String) : void 10: System.out.println("Numbers of friends : " + friends.size());
11:
12: Person firstPerson = friends.get(0);
13: System.out.println("Name of first friend is "+
01: public class Person { firstPerson.getName());
02: 14:
03: private String name; 15: friends.set(1, new Person("Carry"));
04: 16: Person secondPerson = friends.get(1);
05: public Person(String name) { 17: System.out.println("Name of second friend is " +
06: this.name = name; secondPerson.getName());
07: } 18:
08: 19: friends.remove(0);
09: public String getName() { 20: firstPerson = friends.get(0);
10: return name; 21: System.out.println("Name of first friend is " +
11: } firstPerson.getName());
12: 22: }
13: public void setName(String name) { 23: }
14: this.name = name;
15: } Numbers of friends : 2
16: } Name of ﬁrst friend is Alice
Name of second friend is Carry
Name of ﬁrst friend is Carry


23

Copy Array List

01: import java.util.ArrayList;
+ Person 02:
03: public class CopyingArray {
- name : String 04:
06: ArrayList<Person> friends1 = new ArrayList <Person>();
+ Person(String) 07: friends1.add(new Person("Alice"));
+ getName() : String 08: friends1.add(new Person("Bob"));
+ setName(String) : void 09:
10: ArrayList<Person> friends2 = (ArrayList) friends1.clone();
11:
12: friends1.add(0, new Person("Carry"));
01: public class Person { 13:
02: 14: Person firstPerson = friends1.get(0);
03: private String name; 15: System.out.println(firstPerson.getName());
04: 16:
05: public Person(String name) { 17: firstPerson = friends2.get(0);
06: this.name = name; 18: System.out.println(firstPerson.getName());
07: } 19:
08: 20: }
09: public String getName() { 21: }
10: return name;
11: }
12:
13: public void setName(String name) {
14: this.name = name;
15: }
16: }


24

Wrapper Class and Auto-boxing

Primitive Type Wrapper Class 01: import java.util.ArrayList;
byte Byte 02:
03: public class Wrapper {
boolean Boolean
04:
char Char 05: public static void main(String[] args) {
double Double 06: Double wrapper = 29.35;
07: double x = wrapper;
ﬂoat Float
08:
int Integer 09: ArrayList<Double> data = new ArrayList<Double>();
long Long 10: data.add(29.35);
short Short 11: double y = data.get(0);
12: }
13: }

Double@AB1F245H

wrapper @AB1F245H value 29.35
Double
Double


25

Compare Array and Array List Operation

Operation Array ArrayList
Get an element. x = data[4] x = data.get(4)

Replace an element. data[4] = 35; data.set(4, 35);

Number of elements. data.length data.size();

Number of ﬁlled elements. - data.size();

Remove an element. - data.remove(4);

Add an element, growing the
- data.add(35);
collection.

Initializing a collection int[] data = { 1, 4, 9}; -


Computer Programming Chapter 6 : Array and ArrayList

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