YouTipJava Arraylist Containsall
[ Java ArrayList](#)
The `containsAll()` method is used to check if an ArrayList contains all elements from a specified collection.
The syntax for the `containsAll()` method is:
arraylist.containsAll(Collection c);
**Note:** `arraylist` is an object of the ArrayList class.
**Parameter Description:**
* `collection` - The collection parameter.
### Return Value
Returns `true` if the ArrayList contains all elements from the specified collection.
Throws a `ClassCastException` if an element in the ArrayList is incompatible with an element in the specified collection.
Throws a `NullPointerException` if the collection contains a `null` element and the ArrayList does not permit `null` values.
**Note:** You can think of it this way: the `containsAll()` method checks if the collection is a subset of the ArrayList.
### Example
The following example demonstrates the usage of `containsAll`:
## Example
import java.util.ArrayList;
class Main {
public static void main(String[] args){
// Create an ArrayList
ArrayList sites =new ArrayList();
sites.add("Google");
sites.add("");
sites.add("Taobao");
System.out.println("ArrayList 1: "+ sites);
// Create another ArrayList
ArrayList sites2 =new ArrayList();
// Add elements to the ArrayList
sites2.add("");
sites2.add("Google");
System.out.println("ArrayList 2: "+ sites2);
// Check if ArrayList 1 contains all elements of ArrayList 2
boolean result1 = sites.containsAll(sites2);
System.out.println("ArrayList 1 contains all elements of ArrayList 2: "+ result1);
// Check if ArrayList 2 contains all elements of ArrayList 1
boolean result2 = sites2.containsAll(sites);
System.out.println("ArrayList 2 contains all elements of ArrayList 1: "+ result2);
}
}
The output of the above program is:
ArrayList 1: [Google, , Taobao]ArrayList 2: [, Google]ArrayList 1 contains all elements of ArrayList 2: trueArrayList 2 contains all elements of ArrayList 1: false
In the example above, we created two ArrayLists named `sites` and `sites2`.
Notice these lines:
// Returns true sites.containsAll(sites2);// Returns false sites2.containsAll(sites)
The `containsAll()` method checks if `sites` contains all elements from `sites2`. Since it does, it returns `true`.
The `containsAll()` method checks if `sites2` contains all elements from `sites`. Since it does not, it returns `false`.
**The `containsAll()` method between Java ArrayList and HashSet**
## Example
import java.util.ArrayList;
import java.util.HashSet;
class Main {
public static void main(String[] args){
// Create an ArrayList
ArrayList numbers =new ArrayList();
// Insert elements into the ArrayList
numbers.add(1);
numbers.add(2);
numbers.add(3);
System.out.println("ArrayList: "+ numbers);
// Create a HashSet
HashSet primeNumbers =new HashSet();
// Add elements to the HashSet
primeNumbers.add(2);
primeNumbers.add(3);
System.out.println("HashSet: "+ primeNumbers);
// Check if ArrayList contains all elements of HashSet
boolean result1 = numbers.containsAll(primeNumbers);
System.out.println("ArrayList contains all elements of HashSet: "+ result1);
// Check if HashSet contains all elements of ArrayList
boolean result2 = primeNumbers.containsAll(numbers);
System.out.println("HashSet contains all elements of ArrayList: "+ result2);
}
}
The output of the above program is:
ArrayList: [1, 2, 3]HashSet: [2, 3]ArrayList contains all elements of HashSet: trueHashSet contains all elements of ArrayList: false
In the example above, we created an ArrayList named `numbers` and a HashSet named `primeNumbers`.
[ Java ArrayList](#)