Java For Complete Beginners: Step By Step with Full Explanation for Java Beginners by Abdelmoniem Mohammed

Author:Abdelmoniem, Mohammed [Abdelmoniem, Mohammed]
Language: eng
Format: epub
Publisher: Mohammed Abdelmoniem
Published: 2020-09-11T00:00:00+00:00

2nd Override the compareTo() method of Comparable interface. The compareTo() method is used to compare the current object with the specified object.

Let’s say we need to sort the ArrayList<Book> based on year of publication property – first implement Comparable interface and then Override the compareTo method, as shown in the Book2.java file.

Example 14.16 : Book2.java

01 package ch14;

02

03 public class Book2 implements Comparable<Book2>{

04 private String bookName;

05 private int pageNo;

06 private int pubYear;

07

08 public Book2(String bookName, int pageNo, int pubYear){

09 this.bookName = bookName;

10 this.pageNo = pageNo;

11 this.pubYear = pubYear;

12 }

13 public String getBookName(){

14 return bookName;

15 }

16 public void setBookName(String bookName){

17 this.bookName = bookName;

18 }

19 public int getPageNo(){

20 return pageNo;

21 }

22 public void setPageNo(int pageNo){

23 this.pageNo = pageNo;

24 }

25 public int getPubYear(){

26 return pubYear;

27 }

28 public void setPubYear(int pubYear){

29 this.pubYear = pubYear;

30 }

31

32 @Override

33 public String toString(){

34 return ("Book Name = " + bookName + ", Page No = " +

35 pageNo + ", Publish Year = " + pubYear);

36 }

37 @Override

38 public int compareTo(Book2 compareto){

39 int comparepub;

40 comparepub = compareto.getPubYear();

41

42 // For Ascending order

43 return this.pubYear - comparepub;

44 }

45 }

Now we can very well call Collections.sort on ArrayList.

Example 14.17 : BookDemo2.java

01 package ch14;

02

03 import java.util.*;

04

05 public class BookDemo2 {

06 public static void main(String[] args) {

07 ArrayList<Book2> list = new ArrayList<Book2>();

08 list.add(new Book2("C Programming", 552, 2007));

09 list.add(new Book2("How to Design Classes", 666, 2012));

10 list.add(new Book2("Modern C", 222, 2015));

11

12 Collections.sort(list);

13 for (Book2 str1: list) {

14 System.out.println(str1);

15 }

16 }

17 }

Output

Book Name = C Programming, Page No = 552, Publish Year = 2007

Book Name = How to Design Classes, Page No = 666, Publish Year = 2012

Book Name = Modern C, Page No = 222, Publish Year = 2015

As you can see that Book2 array is sorted by publication year in ascending order. If we want sort books by name, we have to change Book2 class to do that:

Example 14.18 : Book2.java (revised version)

01 package ch14;

02

03 public class Book2 implements Comparable<Book2>{

04 private String bookName;

05 private int pageNo;

06 private int pubYear;

07

08 public Book2(String bookName, int pageNo, int pubYear){

09 this.bookName = bookName;

10 this.pageNo = pageNo;

11 this.pubYear = pubYear;

12 }

13 public String getBookName(){

14 return bookName;

15 }

16 public void setBookName(String bookName){

17 this.bookName = bookName;

18 }

19 public int getPageNo(){

20 return pageNo;

21 }

22 public void setPageNo(int pageNo){

23 this.pageNo = pageNo;

24 }

25 public int getPubYear(){

26 return pubYear;

27 }

28 public void setPubYear(int pubYear){

29 this.pubYear = pubYear;

30 }

31

32 @Override

33 public String toString(){

34 return ("Book Name = " + bookName + ", Page No = " +

35 pageNo + ", Publication Year = " + pubYear);

36 }

37 /* @Override

38 // Comparison by publication year

39 public int compareTo(Book2 compareto){

40 int comparepub;

41 comparepub = compareto.getPubYear();

42

43 // For Ascending order

44 return this.pubYear-comparepub;

45 }*/

46

47 @Override

48 // Comparison by name

49 public int compareTo(Book2 compareto){

50 int comparepub;

51 comparepub = compareto.getBookName().compareTo(getBookName());

52 return comparepub;

53 }

54 }

Example 14.19 : DemoBook2.java (revised version)

01 package ch14;

02

03 import java.util.*;

04

05 public class BookDemo2 {

06 public static void main(String[] args) {

07 ArrayList<Book2> list = new ArrayList<Book2>();

08 list.add(new Book2("C Programming", 552, 2007));

09 list.add(new Book2("How to Design Classes", 666, 2012));

10 list.add(new Book2("Modern C", 222, 2015));

11

12 // For Descending order

13 Collections.sort(list);

14 for (Book2 str1: list) {

15 System.

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