Sort Elements using Comparable interface and Comparator interface
There are two way to sort elements in a Collection:
- using Comparable interface
- using Comparator interface
1.Comparable interface exist on java.lang package while Comparator interface exist on java.util package.
2.Comparable interface has one method that name is compareTo() which is single parameterized while Comparator interface has also single method that name is compare() which is double parameterized.
3.When you want to fixed type of sorting you always prefer Comparable interface while if you want to dynamic type of sorting then we always prefer Comparator interface.
4.For example:Contact app is based on comparable while shopping site sorting is based on comparator.
Example of Comparable Interface:Student.java
public class Student implements Comparable<Student> {
private int roll;
private String name;
private float marks;
private String address;
public int getRoll() {
return roll;
}
public void setRoll(int roll) {
this.roll = roll;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public float getMarks() {
return marks;
}
public void setMarks(float marks) {
this.marks = marks;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
@Override
public int compareTo(Student o) {
return name.compareToIgnoreCase(o.getName());
}
}
First.java
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
public class First {
public static void main(String[] args) {
ArrayList<Student> students = new ArrayList();
// create connection
try {
Class.forName("com.mysql.jdbc.Driver");
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/college", "root", "root");
PreparedStatement ps = con.prepareStatement("select * from student");
ResultSet rs = ps.executeQuery();
while (rs.next()) {
Student s = new Student();
s.setRoll(rs.getInt(1));
s.setName(rs.getString(2));
s.setMarks(rs.getFloat(3));
s.setAddress(rs.getString(4));
// add student into collection
students.add(s);
}
} catch (Exception e) {
System.out.println(e);
}
// sort these collection
Collections.sort(students);
Iterator<Student> it = students.iterator();
while (it.hasNext()) {
Student std = it.next();
System.out.println(std.getRoll() + "\t" + std.getName() + "\t" + std.getMarks() + "\t" + std.getAddress());
}
}
}
Table information:
mysql> select * from student;
+------+--------------+-------+-------------+ | roll | name | marks | address | +------+--------------+-------+-------------+ | 1 | deep singh | 67.7 | gzb | | 2 | somesh singh | 79.7 | gzb | | 3 | salim khan | 68.7 | delhi |
Output :
1 deep singh 67.7 gzb 3 salim khan 68.7 delhi 2 somesh singh 79.7 gzbExample of Comparator Interface:
Student.java
public class Student {
private int roll;
private String name;
private float marks;
private String address;
public int getRoll() {
return roll;
}
public void setRoll(int roll) {
this.roll = roll;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public float getMarks() {
return marks;
}
public void setMarks(float marks) {
this.marks = marks;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
}
NameBasedSorting.java
import java.util.Comparator;
public class NameBasedSorting implements Comparator<Student> {
@Override
public int compare(Student o1, Student o2) {
return o1.getName().compareTo(o2.getName());
}
}
First.java
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
public class First {
public static void main(String[] args) {
ArrayList<Student> students = new ArrayList();
// create connection
try {
Class.forName("com.mysql.jdbc.Driver");
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/college", "root", "root");
PreparedStatement ps = con.prepareStatement("select * from student");
ResultSet rs = ps.executeQuery();
while (rs.next()) {
Student s = new Student();
s.setRoll(rs.getInt(1));
s.setName(rs.getString(2));
s.setMarks(rs.getFloat(3));
s.setAddress(rs.getString(4));
// add student into collection
students.add(s);
}
} catch (Exception e) {
System.out.println(e);
}
// sort these collection
Collections.sort(students, new NameBasedSorting());
Iterator<Student> it = students.iterator();
while (it.hasNext()) {
Student std = it.next();
System.out.println(std.getRoll() + "\t" +
std.getName() + "\t" + std.getMarks() + "\t" + std.getAddress());
}
}
}
Output is:
1 deep singh 67.7 gzb 3 salim khan 68.7 delhi 2 somesh singh 79.7 gzb
You can also replace your NameBasedSorting with Annonymous inner class:
// sort these collection
Collections.sort(students, new Comparator<Student>() {
@Override
public int compare(Student o1, Student o2) {
return o1.getName().compareTo(o2.getName());
}
});
You can also replace your annonymous inner class with lambda expression:
// sort these collection using lambda expression Collections.sort(students,(x,y)->x.getName().compareTo(y.getName()));
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