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Java Collections addAll() Method

The addAll(Collection<? super T>, T..) method is used to add all of the specified elements to the specified collection. It helps in adding multiple elements to a collection in one go.

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

public static <T> boolean addAll(Collection<? super T> c, T.. a)

• c − This is the collection into which elements are to be inserted.

• a − This is the elements to insert into c

The method call returns 'true' if the collection changed as a result of the call

• UnsupportedOperationException − This is thrown if c does not support the add method.

• NullPointerException − This is thrown if elements contains one or more null values and c does not support null elements.

• IllegalArgumentException − This is thrown if some aspect of a value in elements prevents it from being added to c.

The following example shows the usage of Java Collection addAll(Collection,T... ) method to add a collection of Integers. We've created a List object with some integers, printed the original list. Using addAll(collection, T...) method, we've added few more elements to the list and then printed the updated list.

package com.tutorialspoint;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class CollectionsDemo {

   public static void main(String[] args) {
      List<Integer> list = new ArrayList<>(Arrays.asList(1,2,3,4,5));

      System.out.println("Initial collection value: " + list);
      // add values to this collection
      Collections.addAll(list, 6, 7, 8);
      System.out.println("Final collection value: "+list);
   }
}

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

Initial collection value: [1, 2, 3, 4, 5]
Final collection value: [1, 2, 3, 4, 5, 6, 7, 8]

The following example shows the usage of Java Collection addAll(Collection,T... ) method to add a collection of Strings. We've created a List object with some strings, printed the original list. Using addAll(collection, T...) method, we've added few more elements to the list and then printed the updated list.

package com.tutorialspoint;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class CollectionsDemo {

   public static void main(String[] args) {
      List<String> list = new ArrayList<>(Arrays.asList("Welcome","to","Tutorialspoint"));

      System.out.println("Initial collection value: " + list);
      // add values to this collection
      Collections.addAll(list, "Simply","Easy","Learning");
      System.out.println("Final collection value: "+list);
   }
}

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

Initial collection value: [Welcome, to, Tutorialspoint]
Final collection value: [Welcome, to, Tutorialspoint, Simply, Easy, Learning]

The following example shows the usage of Java Collection addAll(Collection,T... ) method to add a collection of Student objects. We've created a List object with some students, printed the original list. Using addAll(collection, T...) method, we've added few more elements to the list and then printed the updated list.

package com.tutorialspoint;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class CollectionsDemo {

   public static void main(String[] args) {
      List<Student> list = new ArrayList<>(Arrays.asList(new Student(1, "Julie"),
         new Student(2, "Robert"), new Student(3, "Adam")));

      System.out.println("Initial collection value: " + list);
      // add values to this collection
      Collections.addAll(list, new Student(4, "Jene"), new Student(5, "John"));
      System.out.println("Final collection value: "+list);
   }
}
class 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 + " ]";
   }
}

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

Initial collection value: [[ 1, Julie ], [ 2, Robert ], [ 3, Adam ]]
Final collection value: [[ 1, Julie ], [ 2, Robert ], [ 3, Adam ], [ 4, Jene ], [ 5, John ]]

java_util_collections.htm

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