How to Iterate through Collection Objects in Java? - GeeksforGeeks

07 Jan, 2021
Any group of individual objects which are represented as a single unit is known as the Collection of the objects. In Java, a separate framework named the “Collection Framework” has been defined in JDK 1.2 which holds all the collection classes and interface in it.
The Collection interface (java.util.Collection) and Map interface (java.util.Map) are the two main “root” interfaces of Java collection classes.
How to iterate through Collection Objects?
Using enhanced For loopUsing Iterator methodUsing Simple For loopUsing forEach method
Using enhanced For loop
Using Iterator method
Using Simple For loop
Using forEach method
Method 1: Using enhanced For loop 
Syntax used :
for (datatype variable : collection_used)
Example:
Java
// Java program to demonstrate the// working of enhanced for loop to iterate// collection objects   import java.io.*;import java.util.*;  class GFG {    public static void main(String[] args)    {          // Declaring the ArrayList        Collection<String> gfg = new ArrayList<String>();          // Appending new elements at        // the end of the list        gfg.add("Abhishek Rout");        gfg.add("Vaibhav Kamble");        gfg.add("Anupam Kumar");          // for-each loop for iterating        // unconditionally through collection        for (String name : gfg)            System.out.println("Name : " + name);    }}
Name : Abhishek Rout
Name : Vaibhav Kamble
Name : Anupam Kumar

Method 2: Using Iterator method 
Syntax used :
for (Iterator variable = collection.iterator(); variable.hasNext();)
Example:
Java
// Java program to demonstrate the// working of iterator method to iterate// collection objects   import java.io.*;import java.util.*;  class GFG {    public static void main(String[] args)    {          // Declaring the LinkedList        LinkedList<String> gfg = new LinkedList<String>();          // Appending new elements at        // the end of the list        gfg.add("Abhishek Rout");        gfg.add("Vaibhav Kamble");        gfg.add("Anupam Kumar");          // for loop for iterating        // conditionally through collection        System.out.println("Using For loop");                for (Iterator<String> name = gfg.iterator();             name.hasNext();)                        System.out.println("Name : " + name.next());            // while loop for iterating        // conditionally through collection        System.out.println("\nUsing While Loop");                Iterator<String> name = gfg.iterator();          while (name.hasNext())            System.out.println("Name : " + name.next());    }}
Using For loop
Name : Abhishek Rout
Name : Vaibhav Kamble
Name : Anupam Kumar

Using While Loop
Name : Abhishek Rout
Name : Vaibhav Kamble
Name : Anupam Kumar

Method 3: Using Simple For loop 
Syntax used :
for (int i = 0; i < collection_used.length; i++)
Example:
Java
// Java program to demonstrate the// working of for loop to iterate// collection objects   import java.io.*;import java.util.*;  class GFG {    public static void main(String[] args)    {          // Declaring the ArrayList        Vector<String> gfg = new Vector<String>();          // Appending new elements at        // the end of the list        gfg.add("Abhishek Rout");        gfg.add("Vaibhav Kamble");        gfg.add("Anupam Kumar");          // for loop for iterating        // through collection        for (int i = 0; i < gfg.size(); i++)            System.out.println("Name " + (i + 1) + ": "                               + gfg.get(i));    }}
Name 1: Abhishek Rout
Name 2: Vaibhav Kamble
Name 3: Anupam Kumar

Method 4: Using forEach method 
forEach() method is available in Java 8 and each collection has this method that implements the iteration internally.
Syntax used :
With iterable variable
collection_used.forEach((data_type iterating_variable) -> { System.out.println(iterating_variable); });
Without iterable variable
collection_used.forEach(System.out::println);
Example:
Java
// Java program to demonstrate the// working of forEach method to iterate// collection objects   import java.io.*;import java.util.*;  class GFG {    public static void main(String[] args)    {          // Declaring the ArrayList        ArrayList<String> gfg = new ArrayList<String>();          // Appending new elements at        // the end of the list        gfg.add("Abhishek Rout");        gfg.add("Vaibhav Kamble");        gfg.add("Anupam Kumar");          // forEach for iterating        // through collection        // with iterable variable        System.out.println("With iterable");                gfg.forEach((String name) -> {            System.out.println("Name : " + name);        });          System.out.println("\nWithout iterable");        gfg.forEach(System.out::println);    }}
With iterable
Name : Abhishek Rout
Name : Vaibhav Kamble
Name : Anupam Kumar

Without iterable
Abhishek Rout
Vaibhav Kamble
Anupam Kumar

Java-Collections
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