List in java and how to iterate.

• List is the data structure , which keeps the insertion order preserve
• It allows to store duplicate elements .

List is the interface and it has multiple implementations :

Two popular implementations are below.

• ArrayList
• LinkedList

Let's see how we can create a list .

  List<String> al = new ArrayList<>();
		al.add("rajanikanta");
		al.add("Srikanth");
		al.add("suman");
		al.add("saroj");
		al.add("deepak");

Different ways of Iterating a List:

• Using for loop
• Using enhanced for loop
• Using Iterator
• Using java 8 forEach

Using for loop:

for (int i = 0; i < al.size(); i++) {
			System.out.println(al.get(i));

		}

Using enhanced for loop:

for (String name : al) {
			System.out.println(name);

		

}

Using Iterator:

Iterator<String> itr=al.iterator();
		while(itr.hasNext()) {
			String name=itr.next();
			System.out.println(name);

		}

Using java 8 forEach:

al.forEach(x -> System.out.println(x));

How to remove and add elements while Iteration:

• Using enhanced for loop we can not add and remove elements to the existing list , if we will do so it will leads to ConcurrentModificationException as below.

• Using for loop and Iterator and ListIterator we can add or remove elements from list.

Example using for loop:

for (int i = 0; i < al.size(); i++) {
			if (al.get(i).equals("suman")) {
				al.add("akshay");
			
}

		}

Example using Iterator:

Iterator<String> itr = al.iterator();
		while (itr.hasNext()) {
			String name = itr.next();
			if (name.equals("suman")) {
				itr.remove();
				// Here we can not do like al.remove("suman")
				// We will get ConcurrentModificationException
			}

		}