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One of the Usecase

Question on list of lists

In this posts, we will see how to create a list of lists in java.
You can easily create a list of lists using below syntax

List listOfLists = new ArrayList[];
or
ArrayList listOfLists = new ArrayList[];

One of the Usecase

This is generally useful when you are trying to read a CSV file and then you need to handle list of lists to get it in memory, perform some processing and write back to another CSV file.

Lets take a simple example for list of lists.

package org.arpit.java2blog;

import java.util.ArrayList;

import java.util.List;

public class JavaListOfListsMain {

public static void main[String[] args] {

List listOfLists = new ArrayList[];

ArrayList list1 = new ArrayList[];

list1.add["Delhi"];

list1.add["Mumbai"];

listOfLists.add[list1];

ArrayList anotherList = new ArrayList[];

anotherList.add["Beijing"];

anotherList.add["Shanghai"];

listOfLists.add[anotherList];

listOfLists.forEach[[list]->

{

list.forEach[[city]->System.out.println[city]];

}

];

}

When you run above program, you will get below output.

Delhi
Mumbai
Beijing
Shanghai

Question on list of lists

Can you instantiate List as below

List myList = new ArrayList[];

No, you can't.

Lets understand the reason for it.
Lets say you have list as below:

ArrayList list1 = new ArrayList[];

Now suppose you could assign that to

List list2 = list1.

Now, you should be able to do this:

list2.add[new LinkedList[]];

But that means you have just added a LinkedList to a list whose elements are supposed to be ArrayList only.Thats why it is not allowed to do it.
Thats all about how to create list of lists in java.

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One of the Usecase

Question on list of lists

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