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Text lesson

retainAll()

Example

The retainAll() method removes items from a list that are not present in a specified collection.

import java.util.ArrayList;
public class Main {
  public static void main(String[] args) {
    ArrayList<String> cars = new ArrayList<String>();
    cars.add("Volvo");
    cars.add("BMW");
    cars.add("Ford");
    cars.add("Mazda");
    cars.add("Toyota");
    ArrayList<String> valid = new ArrayList<String>();
    valid.add("Volvo");
   valid.add("Ford");
    valid.add("Mazda");
    cars.retainAll(valid);
    System.out.println(cars);
 }
}

Definition and Usage

The retainAll() method removes from a list all items that are not part of a specified collection.

Syntax

public boolean retainAll(Collection items)

Parameter Values

Parameter

Description

items

Required: A collection containing the items to retain in the list, with all other items being removed.

Technical Details

Returns:

True if the list has been modified; false otherwise.

Throws:

NullPointerException occurs if the collection is null.