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Collection(TreeSet)

TreeSet:-TreeSet is an implemented class of Set interface where TreeSet is a group of individual objects as a single entity where duplicates are not allowed but insertion should be according to some sorting order and elements must be comparable. If we are not writing some additional code for sorting than automatically elements insert according to the default natural sorting (ascending order for numbers), if we want to customize sorting than we have to implements Comparator interface present in java.util package and implements compare method. Default natural sorting is done by the comparable interface which is present in java.lang package, having only one method compareTo.

Example1:-TestTreeSet.java
import java.util.*;
class TestTreeSet
{
public static void main(String[]args)
{
TreeSet ts=new TreeSet();
ts.add(50);
ts.add(40);
ts.add(60);
ts.add(30);
ts.add(70);
ts.add(20);
ts.add(80);
ts.add(10);
System.out.println(ts);
Iterator itr=ts.iterator();
while(itr.hasNext())
{
System.out.println(itr.next());
}
}
}
Output:-
C:\JAVATECH>javac TestTreeSet.java
C:\JAVATECH>java TestTreeSet
[10, 20, 30, 40, 50, 60, 70, 80]
10
20
30
40
50
60
70
80

Example2:- TestTreeSet.java
import java.util.*;
class TestTreeSet
{
public static void main(String[]args)
{
TreeSet ts=new TreeSet();
ts.add("Mango");
ts.add("Orange");
ts.add("Graps");
ts.add("Apple");
ts.add("Bhupendra");
ts.add("bhupendra");
ts.add("apple");
System.out.println(ts);
Iterator itr=ts.iterator();
while(itr.hasNext())
{
System.out.println(itr.next());
}
}
}
Output:-
C:\JAVATECH>javac TestTreeSet.java
C:\JAVATECH>java TestTreeSet
[Apple, Bhupendra, Graps, Mango, Orange, apple, bhupendra]
Apple
Bhupendra
Graps
Mango
Orange
apple
bhupendra
If we want to customize sorting then we have to implements Comparator interface and implements compare method.
Example3:- TreeSort.java
import java.util.*;
class Student
{
int id;
String name,course;
Student(int id,String name,String course)
{
this.id=id;
this.name=name;
this.course=course;
}
}
class MyComp implements Comparator<Student>
{
public int compare(Student p,Student q)
{
if(p.id>q.id)
{
return -1;
}
else
{
return 1;
}
}
}
class TreeSort
{
public static void main(String[]args)
{
TreeSet <Student>tr=new TreeSet<Student>(new MyComp());
Student s1=new Student(101,"amit","MCA");
Student s2=new Student(102,"sumit","MA");
Student s3=new Student(103,"sachin","BCA");
Student s4=new Student(104,"neha","M-Tech");
tr.add(s1);
tr.add(s2);
tr.add(s3);
tr.add(s4);
Iterator itr=tr.iterator();
while(itr.hasNext())
{
Student s=(Student)itr.next();
System.out.println(s.id+"     "+s.name+"     "+s.course);
}
}
}
Output:-
C:\JAVATECH>javac TreeSort.java
C:\JAVATECH>java TreeSort
101     amit     MCA
102     sumit     MA
103     sachin    BCA
104     neha     M-Tech
Example4:- TreeSort.java
import java.util.*;
class Student
{
int id;
String name,course;
Student(int id,String name,String course)
{
this.id=id;
this.name=name;
this.course=course;
}
}
class MyComp implements Comparator<Student>
{
public int compare(Student p,Student q)
{
if(p.id>q.id)
{
return -1;
}
else
{
return 1;
}
}
}
class TreeSort
{
public static void main(String[]args)
{
TreeSet <Student>tr=new TreeSet<Student>(new MyComp());
Student s1=new Student(101,"amit","MCA");
Student s2=new Student(102,"sumit","MA");
Student s3=new Student(103,"sachin","BCA");
Student s4=new Student(104,"neha","M-Tech");
tr.add(s1);
tr.add(s2);
tr.add(s3);
tr.add(s4);
Iterator itr=tr.iterator();
while(itr.hasNext())
{
Student s=(Student)itr.next();
System.out.println(s.id+"     "+s.name+"     "+s.course);
}
}
}
Output:-
C:\JAVATECH>javac TreeSort.java
C:\JAVATECH>java TreeSort
104     neha    M-Tech
103     sachin     BCA
102     sumit     MA

101     amit     MCA
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