Java ArrayList.removeIf()

The ArrayList.removeIf() iterates the list and removes all of the elements of this ArrayList that satisfy the given Predicate.

1. ArrayList.removeIf() API

The removeIf() takes a single argument of type Predicate. The Predicate interface is a functional interface that represents a condition (boolean-valued function) of one argument. It checks that is a given argument met the condition or not.

public boolean removeIf(Predicate<? super E> filter);

Method parameter – filter predicate that returns true for elements to be removed.
Method returnstrue if any elements were removed from this list.
Method throwsNullPointerException if predicate is null.

2. ArrayList.removeIf() Example

The following Java programs use removeIf() method to remove elements that match a Predicate.

2.1. Remove All Even Numbers

In this simple example, we have a list of odd/even numbers and remove all even numbers from the list.

ArrayList<Integer> numbers = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10));

numbers.removeIf(number -> number % 2 == 0);

System.out.println(numbers);

Program output.

[1, 3, 5, 7, 9]

2.2. Remove Objects by Field

In this simple example, we have a list of employees, and we are removing all employees whose names start with char 'P'. The predicate, employee.getName().startsWith(“P”) matches the name of each Employee and returns true if the name starts with P.

ArrayList<Employee> employees = new ArrayList<>();

employees.add(new Employee(1l, "Alex", LocalDate.of(2018, Month.APRIL, 21)));
employees.add(new Employee(4l, "Brian", LocalDate.of(2018, Month.APRIL, 22)));
employees.add(new Employee(3l, "Piyush", LocalDate.of(2018, Month.APRIL, 25)));
employees.add(new Employee(5l, "Charles", LocalDate.of(2018, Month.APRIL, 23)));
employees.add(new Employee(2l, "Pawan", LocalDate.of(2018, Month.APRIL, 24)));

Predicate<Employee> condition = employee -> employee.getName().startsWith("P");

employees.removeIf(condition);

System.out.println(employees);

Program output.

[
	Employee [id=1, name=Alex, dob=2018-04-21],
	Employee [id=4, name=Brian, dob=2018-04-22],
	Employee [id=5, name=Charles, dob=2018-04-23]
]

That’s all for the ArrayList removeIf() in Java.

Happy Learning !!

Read More: ArrayList Java Docs and Predicate Java Docs

Sourcecode on Github

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