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Traverse Through ArrayList in Forward Direction in Java

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  • Last Updated : 11 Dec, 2020

ArrayList is a part of the collection framework and is present in java.util package. It provides us with dynamic arrays in Java. The listIterator() method of java.util.ArrayList class is used to return a list iterator over the elements in this list (in a proper organized sequence). ArrayList can be traversed in the forward direction using multiple ways.

Example:

Input : ArrayList: [5, 6, 8, 10]
Output:
Value is : 5
Value is : 6
Value is : 8
Value is : 10

Approach 1: Using listIterator Method

  1. Create a list iterator object of a given ArrayList.
  2. Use while loop with the condition as hasNext() method.
  3. If hasNext() method returns false, loop breaks.
  4. Else print the value using object.next() method.

Example:

Java




// Traverse through ArrayList in
// forward direction using Java
import java.util.*;
import java.io.*;
  
class GFG {
    public static void main(String[] args)
    {
        ArrayList<Integer> alist = new ArrayList<>();
  
        // adding element to arrlist
        alist.add(5);
        alist.add(6);
        alist.add(8);
        alist.add(10);
  
        ListIterator<Integer> it = alist.listIterator();
  
        while (it.hasNext()) {
            System.out.println("Value is : " + it.next());
        }
    }
}


Output

Value is : 5
Value is : 6
Value is : 8
Value is : 10

Time Complexity: O(N), where N is the length of ArrayList.

Approach 2: Using For Loop

Print all the values in ArrayList using for loop. Size of ArrayList can be obtained using ArrayList.size() method and for accessing the element use ArrayList.get() method. 

Implementation:

Java




// Traverse through ArrayList in
// forward direction using Java
import java.util.*;
import java.io.*;
  
class GFG {
    public static void main(String[] args)
    {
        ArrayList<Integer> alist = new ArrayList<>();
  
        // adding element to arrlist
        alist.add(5);
        alist.add(6);
        alist.add(8);
        alist.add(10);
  
        for (int i = 0; i < alist.size(); i++)
            System.out.println("Value is : "
                               + alist.get(i));
    }
}


Output

Value is : 5
Value is : 6
Value is : 8
Value is : 10

Time Complexity: O(N), where N is the length of ArrayList.

Approach 3: Using forEach Loop

Print all the values in ArrayList using for each loop.

Example:

Java




// Traverse through ArrayList in
// forward direction using Java
import java.util.*;
import java.io.*;
  
class GFG {
    public static void main(String[] args)
    {
        ArrayList<Integer> alist = new ArrayList<>();
  
        // adding element to arrlist
        alist.add(5);
        alist.add(6);
        alist.add(8);
        alist.add(10);
  
        for (Integer i : alist)
            System.out.println("Value is : " + i);
    }
}


Output

Value is : 5
Value is : 6
Value is : 8
Value is : 10

Time Complexity: O(N), where N is the length of ArrayList.

Approach 4: Using Lambda Function

Print all the values in ArrayList using the lambda function.

Example:

Java




// Traverse through ArrayList in
// forward direction using Java
import java.util.*;
import java.io.*;
  
class GFG {
    public static void main(String[] args)
    {
        ArrayList<Integer> alist = new ArrayList<>();
  
        // adding element to arrlist
        alist.add(5);
        alist.add(6);
        alist.add(8);
        alist.add(10);
        // lambda
        alist.forEach(
            i -> System.out.println("Value is : " + i));
    }
}


Output

Value is : 5
Value is : 6
Value is : 8
Value is : 10

Time Complexity: O(N), where N is the length of ArrayList.


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