Read Also: 5 ways: How to iterate ArrayList
1. Create a list of lists in Java with Example
Given below is the simplest way to create a list of lists in Java:For String:
List<List<String>> listOfLists = new ArrayList<>();
That's it. The above line will create a list of lists of String.
For Integer:
List<List<Integer>> listOfLists = new ArrayList<>();
The above line will create a list of lists of Integer.
Read Also: Convert LinkedList to ArrayList
1.1 Example of String and Integer list of lists in Java:
1. Given below is an example of String list of lists:
import java.util.*;
public class JavaHungry
{
public static void main(String[] args)
{
// Create listOfLists in Java
List<List<String>> listOfLists = new ArrayList<>();
// Creating innerList
List<String> innerList = new ArrayList<>();
// Adding elements to innerList
innerList.add("Boston");
innerList.add("San Francisco");
innerList.add("New York");
// Adding innerList to listOfLists
listOfLists.add(innerList);
// Creating another inner list
List<String> innerList2 = new ArrayList<>();
// Adding elements to innerList2
innerList2.add("LinkedIn");
innerList2.add("Twitter");
innerList2.add("Facebook");
// Adding innerList2 to listOfLists
listOfLists.add(innerList2);
// Printing listOfLists elements
System.out.println(listOfLists);
}
}
Output:
[[Boston, San Francisco, New York], [LinkedIn, Twitter, Facebook]]
2. Given below is an example of Integer list of lists:
import java.util.*;
public class JavaHungry
{
public static void main(String[] args)
{
// Create listOfLists in Java
List<List<Integer>> listOfLists = new ArrayList<>();
// Creating innerList
List<Integer> innerList = new ArrayList<>();
// Adding elements to innerList
innerList.add(1);
innerList.add(2);
innerList.add(3);
// Adding innerList to listOfLists
listOfLists.add(innerList);
// Creating another inner list
List<Integer> innerList2 = new ArrayList<>();
// Adding elements to innerList2
innerList2.add(100);
innerList2.add(101);
innerList2.add(102);
// Adding innerList2 to listOfLists
listOfLists.add(innerList2);
// Printing listOfLists elements
System.out.println(listOfLists);
}
}
Output:
[[1, 2, 3], [100, 101, 102]]
2. Iterate list of lists in Java with Example
There are two ways through which you can iterate the list of lists in Java.a. Using nested advance for loop
b. Using forEach (after Java 8)
2.1 Iterate using nested advance for loop
/* Iterating listOfLists elements
using advance for loops */ for(List innerlist : listOfLists)
{
for(Object i : innerlist)
{
System.out.print( i+ " ");
}
System.out.println("");
}
Output:
1 2 3
100 101 102
2.2 Iterate using Java8 forEach
/* Iterating listOfLists elements
using Java8 forEach*/ listOfLists.forEach((list) -> {
list.forEach((num) -> System.out.println(num));
});
Output:
1
2
3
100
101
102
That's all for today, please mention in comments in case you have any questions related to create and iterate the list of lists in java with examples.