Today we will learn how to create a Java array of ArrayList. We will also learn how to create an ArrayList of array elements.
Creating array of list in java is not complex. Below is a simple program showing java Array of ArrayList example.
import java.util.ArrayList;
import java.util.List;
public class JavaArrayOfArrayList {
public static void main(String[] args) {
List<String> l1 = new ArrayList<>();
l1.add("1");
l1.add("2");
List<String> l2 = new ArrayList<>();
l2.add("3");
l2.add("4");
l2.add("5");
List<String>[] arrayOfList = new List[2];
arrayOfList[0] = l1;
arrayOfList[1] = l2;
for (int i = 0; i < arrayOfList.length; i++) {
List<String> l = arrayOfList[i];
System.out.println(l);
}
}
}
Notice that we can’t use generics while creating the array because java doesn’t support generic array. So if we try to use below code, it will produce compile time error as “Cannot create a generic array of List<String>”.
List<String>[] arrayOfList = new List<String>[2];
We can also create an array whose elements are a list. Below is a simple example showing how to create a list of array elements in java.
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public class JavaArrayListOfStringArray {
public static void main(String[] args) {
// List of String arrays
List<String[]> list = new ArrayList<String[]>();
String[] arr1 = { "a", "b", "c" };
String[] arr2 = { "1", "2", "3", "4" };
list.add(arr1);
list.add(arr2);
// printing list of String arrays in the ArrayList
for (String[] strArr : list) {
System.out.println(Arrays.toString(strArr));
}
}
}
If you are not sure about the type of objects in the array or you want to create an ArrayList of arrays that can hold multiple types, then you can create an ArrayList of an object array. Below is a simple example showing how to create ArrayList of object arrays in java.
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public class JavaArrayListOfObjectArray {
public static void main(String[] args) {
// list of Object arrays to hold different types of array
List<Object[]> list = new ArrayList<Object[]>();
String[] arr1 = { "a", "b", "c" };
String[] arr2 = { "1", "2", "3", "4" };
JavaArrayListOfObjectArray aa = new JavaArrayListOfObjectArray();
JavaArrayListOfObjectArray.A[] arr3 = { aa.new A("AA"), aa.new A("BB") };
list.add(arr1);
list.add(arr2);
list.add(arr3);
// list holds different types of Object arrays, let's print them
for (Object[] objArr : list) {
System.out.println(Arrays.toString(objArr));
// iterating over the array and doing operation based on it's type
for (Object obj : objArr) {
// using instanceof keyword to find the Object type in the array
if (obj instanceof String) {
// doSomethingForStringObject();
} else if (obj instanceof JavaArrayListOfObjectArray.A) {
// doSomethingForAObject();
}
}
}
}
/**
* A sample class to use in arraylist of arrays
*
* @author pankaj
*
*/
public class A {
private String name;
public A(String n) {
this.name = n;
}
public String getName() {
return this.name;
}
@Override
public String toString() {
return "A.class::"+this.name;
}
}
}
When we execute the above program, it produces the following output.
[a, b, c]
[1, 2, 3, 4]
[A.class::AA, A.class::BB]
That’s all for creating an Array of ArrayList and ArrayList of Array in Java.
You can checkout more core java examples from our GitHub Repository.
Reference: Java Arrays
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On the space below, write down the code for declaring an integer array whare the values are 1,4,3,5and 6.
- Narzde Sam
Can someone help me out with simple coding with ARRAYS
- Eldridge Gee
how i can remove specific value on list of array string?
- Annisa Nurika
Thank you very much Pankaj this example is very clear and very helpful.
- Lithi P
Dear Pankaj, Very usefull your article. As I have told you the last time in my email to you. With this article, I have an idea developped below: - Create an arraylist: ArrayList dico = new ArrayList(); String[2] is a table of two String elements which represents ‘value of word attribute’ and 'value of the word"s definition". -But i don’t know how to populate my list ‘dico’. Please give me your solution. I wait your response. Thank in advance. Vu
- vu