- Java.util Package Classes
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- Java.util - TreeSet
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- Java.util Package Extras
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Java TreeSet descendingSet() Method
Description
The Java TreeSet descendingSet() method is used to return a reverse order view of the elements contained in this set. The descending set is backed by this set, so changes to the set are also reflected in the descending set and reverse.
Declaration
Following is the declaration for java.util.TreeSet.descendingSet() method.
public NavigableSet<E> descendingSet()
Parameters
NA
Return Value
The method call returns a reverse order view of this set.
Exception
NA
Getting Descending TreeSet of a TreeSet of Integer Example
The following example shows the usage of Java TreeSet descendingSet() method to get a set from this set having elements in descending order. We've created two TreeSet objects of Integer. Then few entries are added using add() method to one set. Using descendingIterator(), we've received an iterator and iterated trough its value.
package com.tutorialspoint; import java.util.TreeSet; public class TreeSetDemo { public static void main(String[] args) { // creating a TreeSet TreeSet<Integer> treeadd = new TreeSet<>(); TreeSet<Integer> treereverse = new TreeSet<>(); // adding in the tree set treeadd.add(1); treeadd.add(13); treeadd.add(17); treeadd.add(2); // creating reverse set treereverse = (TreeSet)treeadd.descendingSet(); // displaying the Tree set data System.out.println("Tree set data in reverse order: " + treereverse); } }
Output
Let us compile and run the above program, this will produce the following result.
Tree set data in reverse order: [17, 13, 2, 1]
Getting Descending TreeSet of a TreeSet of String Example
The following example shows the usage of Java TreeSet descendingSet() method to get a set from this set having elements in descending order. We've created two TreeSet objects of String. Then few entries are added using add() method to one set. Using descendingIterator(), we've received an iterator and iterated trough its value.
package com.tutorialspoint; import java.util.TreeSet; public class TreeSetDemo { public static void main(String[] args) { // creating a TreeSet TreeSet<String> treeadd = new TreeSet<>(); TreeSet<String> treereverse = new TreeSet<>(); // adding in the tree set treeadd.add("A"); treeadd.add("B"); treeadd.add("C"); treeadd.add("D"); // creating reverse set treereverse = (TreeSet)treeadd.descendingSet(); // displaying the Tree set data System.out.println("Tree set data in reverse order: " + treereverse); } }
Output
Let us compile and run the above program, this will produce the following result.
Tree set data in reverse order: [D, C, B, A]
Getting Descending TreeSet of a TreeSet of Object Example
The following example shows the usage of Java TreeSet descendingSet() method to get a set from this set having elements in descending order. We've created two TreeSet objects of String. Then few entries are added using add() method to one set. Using descendingIterator(), we've received an iterator and iterated trough its value.
package com.tutorialspoint; import java.util.TreeSet; public class TreeSetDemo { public static void main(String[] args) { // creating a TreeSet TreeSet<Student> treeadd = new TreeSet<>(); TreeSet<Student> treereverse = new TreeSet<>(); // adding in the tree set treeadd.add(new Student(1, "Robert")); treeadd.add(new Student(2, "Julie")); treeadd.add(new Student(3, "Adam")); treeadd.add(new Student(4, "Julia")); // creating reverse set treereverse = (TreeSet)treeadd.descendingSet(); // displaying the Tree set data System.out.println("Tree set data in reverse order: " + treereverse); } } class Student implements Comparable<Student> { int rollNo; String name; Student(int rollNo, String name){ this.rollNo = rollNo; this.name = name; } @Override public String toString() { return "[ " + this.rollNo + ", " + this.name + " ]"; } @Override public boolean equals(Object obj) { Student s = (Student)obj; return this.rollNo == s.rollNo && this.name.equalsIgnoreCase(s.name); } @Override public int compareTo(Student student) { return this.rollNo - student.rollNo; } }
Output
Let us compile and run the above program, this will produce the following result.
Tree set data in reverse order: [[ 4, Julia ], [ 3, Adam ], [ 2, Julie ], [ 1, Robert ]]
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