The addAll(Collection) method of Stack Class is used to append all of the elements from the collection passed as a parameter to this function to the end of a Stack keeping in mind the order of return by the collection’s iterator.
Syntax:
boolean addAll(Collection C)
Parameters: The method accepts a mandatory parameter C which is a collection of ArrayList. It is the collection whose elements are needed to be appended at the end of the Stack.
Return Value: The method returns True if at least one action of append is performed, else False.
Below program illustrate the Java.util.Stack.addAll() method:
// Java code to illustrate boolean addAll()import java.util.*;import java.util.ArrayList;  public class GFG {    public static void main(String args[])    {          // Creating an empty Stack        Stack<String> stack = new Stack<String>();          // Use add() method to add elements in the Stack        stack.add("Geeks");        stack.add("for");        stack.add("Geeks");        stack.add("10");        stack.add("20");          // A collection is created        Collection<String> c = new ArrayList<String>();        c.add("A");        c.add("Computer");        c.add("Portal");        c.add("for");        c.add("Geeks");          // Displaying the Stack        System.out.println("The Stack is: " + stack);          // Appending the collection to the Stack        stack.addAll(c);          // Clearing the Stack using clear() and displaying        System.out.println("The new Stack is: " + stack);    }} |
Output:
The Stack is: [Geeks, for, Geeks, 10, 20] The new Stack is: [Geeks, for, Geeks, 10, 20, A, Computer, Portal, for, Geeks]
Example 2:
// Java code to illustrate// boolean add(Object element)  import java.util.*;  public class StackDemo {    public static void main(String args[])    {          // Creating an empty Stack        Stack<Integer> stack            = new Stack<Integer>();          // Use add() method        // to add elements in the Stack        stack.add(10);        stack.add(20);        stack.add(30);        stack.add(40);        stack.add(50);          // A collection is created        Collection<Integer> c = new ArrayList<Integer>();        c.add(1);        c.add(2);        c.add(3);          // Displaying the Stack        System.out.println("The Stack is: " + stack);          // Appending the collection to the Stack        stack.addAll(c);          // Clearing the Stack using clear() and displaying        System.out.println("The new Stack is: " + stack);    }} |
Output:
The Stack is: [10, 20, 30, 40, 50] The new Stack is: [10, 20, 30, 40, 50, 1, 2, 3]
