Learn to remove and update elements of a Collection using Stream API in Java with examples. It is worth noting that each method shown below creates a new List, the original List is not modified after the processing.
1. Removing Elements using Stream
Removing the elements is very simple. We iterate over the Stream elements and filter out the elements that match a given Predicate passed to the Stream.filter() method.
In the following example, we are only selecting the employees whose names start with the character “A“. All other elements are removed from the stream.
List<Employee> list = List.of(
new Employee(1, "Alex", LocalDate.of(1990, 1, 2), 100d),
new Employee(2, "Alok", LocalDate.of(1992, 1, 2), 200d),
new Employee(3, "Brian", LocalDate.of(1994, 1, 2), 300d),
new Employee(4, "Charles", LocalDate.of(1996, 1, 2), 400d));
List<Employee> modifiedList = list.stream()
.filter(e -> e.getName().startsWith("A"))
.collect(Collectors.toList());
//Employees whose names start with "A"
System.out.println(modifiedList);The program output.
[
Employee [id=1, name=Alex, dateOfBirth=1990-01-02, salary=100.0],
Employee [id=2, name=Alok, dateOfBirth=1992-01-02, salary=200.0]
]2. Updating Elements using Stream
To update all elements or the matching elements from the Stream, we use the Stream.map() method and return a new Employee instance. All modified instances are collected into a new List.
In the following example, we are updating the salary for all employees by 100. The modified elements are collected into newList.
List<Employee> list = List.of(
new Employee(1, "Alex", LocalDate.of(1990, 1, 2), 100d),
new Employee(2, "Alok", LocalDate.of(1992, 1, 2), 200d),
new Employee(3, "Brian", LocalDate.of(1994, 1, 2), 300d),
new Employee(4, "Charles", LocalDate.of(1996, 1, 2), 400d));
List<Employee> newList = list.stream()
.map(e -> {
e.setSalary(e.getSalary() + 100);
return e;
})
.collect(Collectors.toList());
System.out.println(newList);The program output.
[
Employee [id=1, name=Alex, dateOfBirth=1990-01-02, salary=200.0],
Employee [id=2, name=Alok, dateOfBirth=1992-01-02, salary=300.0],
Employee [id=3, name=Brian, dateOfBirth=1994-01-02, salary=400.0],
Employee [id=4, name=Charles, dateOfBirth=1996-01-02, salary=500.0]
]3. Conclusion
In this quick Java tutorial, we learned to remove the elements from List using Java 8 Stream.filter(). We also learned to update the elements of a Stream using Stream.map() method.
Happy Learning !!