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Java Method Overloading Comprehensive Java ArrayList Methods

Java ArrayList containsAll() usage and example

Java ArrayList Methods

Java ArrayList containsAll() method checks whether the ArrayList contains all elements of the specified collection.

The syntax of containsAll() method is:

arraylist.containsAll(Collection c);

containsAll() parameters

collection - Check if all elements of the collection appear in the ArrayList.

containsAll() return value

If the ArrayList contains all elements of the specified collection, then return true
If the class of the existing elements in the ArrayList is not compatible with the class of the elements in the specified collection, then a ClassCastException is thrown
If the collection contains null elements and the ArrayList does not allow null values, then a NullPointerException is thrown

Note：The containsAll() method checks whether the collection is a subset of the ArrayList.

Example1：Java ArrayList containsAll()

Example

import java.util.ArrayList;
class Main {
　　　　public static void main(String[] args) {
　　　　　　　　//Create ArrayList
　　　　　　　　ArrayList<String> languages1　= new ArrayList<>();
　　　　　　　　//Add element to ArrayList
　　　　　　　　languages1.add("JavaScript");
　　　　　　　　languages1.add("Python");
　　　　　　　　languages1.add("Java");
　　　　　　　　System.out.println("ArrayList　1: "　+　languages1;
　　　　　　　　//Create another ArrayList
　　　　　　　　ArrayList<String> languages2　= new ArrayList<>();
　　　　　　　　//Add element to ArrayList
　　　　　　　　languages2.add("Java");
　　　　　　　　languages2.add("Python");
　　　　　　　　System.out.println("ArrayList　2: "　+　languages2;
　　　　　　　　//　Check the ArrayList　1Whether the ArrayList　2　
　　　　　　　　boolean result1　= languages1.containsAll(languages2;
　　　　　　　　System.out.println("ArrayList　1contains ArrayList　2All elements of : "　+　result1;
　　　　　　　　//　Check the ArrayList　2Whether the ArrayList　1　
　　　　　　　　boolean result2　= languages2.containsAll(languages1;
　　　　　　　　System.out.println("ArrayList　2contains ArrayList　1All elements of : "　+　result2;
　　　　}
}

Output result

ArrayList　1: [JavaScript, Python, Java]
ArrayList　2: [Java, Python]
　ArrayList　1contains ArrayList　2All elements of : true
　ArrayList　2contains ArrayList　1elements: false

In the above example, we created two named languages1and languages2of the ArrayList. Note the expression

//　Returns true
languages1.containsAll(languages2)

Here, the containsAll() method checks languages1whether it contains languages2elements. Therefore, this method returns true. However, please note the following expression:

//　Returns false
languages2.containsAll(languages1)

Here, the containsAll() method checks languages2whether it contains languages1elements. Therefore, it returns false

Note：The containsAll() method is not specific to the ArrayList class. It inherits from the List interface.

Example2：Java ArrayList and HashSet between containsAll()

Example

import java.util.ArrayList;
import java.util.HashSet;
class Main {
　　　　public static void main(String[] args) {
　　　　　　　　//Create ArrayList
　　　　　　　　ArrayList<Integer> numbers = new ArrayList<>();
　　　　　　　　//Add element to ArrayList
　　　　　　　　numbers.add(1;
　　　　　　　　numbers.add(2;
　　　　　　　　numbers.add(3;
　　　　　　　　System.out.println("ArrayList: "　+　numbers);
　　　　　　　　//Create HashSet
　　　　　　　　HashSet<Integer> primeNumbers = new HashSet<>();
　　　　　　　　//Add element to 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;
　　　　}
}

Output result

ArrayList: [1,　2,　3]
HashSet: [2,　3]
ArrayList contains all elements of HashSet : true
HashSet contains all elements of ArrayList : false

In the above example, we created an ArrayList named numbers and a HashSet named primeNumbers. Note these expressions,

//　Check if ArrayList contains HashSet　
//　Returns true
numbers.containsAll(primeNumbers)
//　Check if HashSet contains ArrayList　
//　Returns false
primeNumbers.containsAll(numbers)

NoteWe can use Java ArrayList retainAll() MethodGet the common elements between ArrayList and HashSet.

Java ArrayList Methods

Java Method Overloading Comprehensive Java ArrayList Methods