Java TreeSet addAll() Method

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Description

The Java TreeSet addAll(Collection c) method is used to add all of the elements in the specified collection to this set.

Declaration

Following is the declaration for java.util.TreeSet.addAll() method.

public boolean addAll(Collection c)

Parameters

c − These are the elements to be added.

Return Value

The method call returns true if this set changed as a result of the call.

Exception

• ClassCastException − This exception is thrown if the elements provided cannot be compared with the elements currently in the set.

• NullPointerException − This exception is thrown if the specified collection is null.

Adding Multiple Entries to a TreeSet of Integer Example

The following example shows the usage of Java TreeSet addAll() method to add multiple entries to the treeset in one go. We've created a TreeSet object of Integer. Then few entries are added using add() method to the treeset objects. Then first treeset is populated using addAll() method and then treeset is printed to validate the contents.

package com.tutorialspoint;

import java.util.TreeSet;

public class TreeSetDemo {
   public static void main(String[] args) {

      // creating a TreeSet 
      TreeSet <Integer>treeone = new TreeSet<>();
      TreeSet <Integer>treetwo = new TreeSet<>();

      // adding in the treeone
      treeone.add(12);
      treeone.add(13);
      treeone.add(14);

      // adding in the treetwo
      treetwo.add(15);
      treetwo.add(16);
      treetwo.add(17);  

      // adding treetwo to treeone
      treeone.addAll(treetwo);
	  
      // displaying the Tree set data
      System.out.print("Tree set : " + treeone);
   }    
}

Output

Let us compile and run the above program, this will produce the following result.

Tree set : [12, 13, 14, 15, 16, 17]

Adding Multiple Entries to a TreeSet of String Example

The following example shows the usage of Java TreeSet addAll() method to add multiple entries to the treeset in one go. We've created a TreeSet object of String. Then few entries are added using add() method to the treeset objects. Then first treeset is populated using addAll() method and then treeset is printed to validate the contents.

package com.tutorialspoint;

import java.util.TreeSet;

public class TreeSetDemo {
   public static void main(String[] args) {

      // creating a TreeSet 
      TreeSet <String>treeone = new TreeSet<>();
      TreeSet <String>treetwo = new TreeSet<>();

      // adding in the treeone
      treeone.add("12");
      treeone.add("13");
      treeone.add("14");

      // adding in the treetwo
      treetwo.add("15");
      treetwo.add("16");
      treetwo.add("17");  

      // adding treetwo to treeone
      treeone.addAll(treetwo);
	  
      // displaying the Tree set data
      System.out.print("Tree set : " + treeset);
   }    
}

Output

Let us compile and run the above program, this will produce the following result.

Tree set : [12, 13, 14, 15, 16, 17]

Adding Multiple Entries to a TreeSet of Object Example

The following example shows the usage of Java TreeSet addAll() method to add multiple entries to the treeset in one go. We've created a TreeSet object of Student objects. Then few entries are added using add() method to the treeset objects. Then first treeset is populated using addAll() method and then treeset is printed to validate the contents.

package com.tutorialspoint;

import java.util.TreeSet;

public class TreeSetDemo {
   public static void main(String[] args) {

      // creating a TreeSet 
      TreeSet <Student>treeone = new TreeSet<>();
      TreeSet <Student>treetwo = new TreeSet<>();

      // adding in the treeone
      treeone.add(new Student(1, "Robert"));
      treeone.add(new Student(2, "Julie"));  
      treeone.add(new Student(3, "Adam"));

      // adding in the treetwo
      treetwo.add(new Student(4, "Julia"));
      treetwo.add(new Student(5, "Alfred"));  
      treetwo.add(new Student(6, "John")); 

      // adding treetwo to treeone
      treeone.addAll(treetwo);
	  
      // displaying the Tree set data
      System.out.print("Tree set : " + treeone);
   }    
}
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 : [[ 1, Robert ], [ 2, Julie ], [ 3, Adam ], [ 4, Julia ], [ 5, Alfred ], [ 6, John ]]