Java 8 & Streams · Chapter 02

Filtering

filter() with Predicates, findFirst vs findAny, anyMatch/allMatch/noneMatch and short-circuiting — with Spring Boot examples.

◷ 6 min read§ 11 sections? 6 interview questions{ } 19 code examples

#Introduction

Filtering is one of the most frequently used Stream operations in real-world Java projects and interviews. By the end of this chapter you should be able to answer:

What is filter()?
When should I use findFirst() vs findAny()?
What are anyMatch(), allMatch() and noneMatch()?
How do these work internally?
Where are they used in Spring Boot projects?

#The filter() Operation

filter() selects elements that satisfy a condition.

Java

stream.filter(predicate)

A Predicate<T> is a functional interface:

Java

boolean test(T t);

Even Numbers

Java

List<Integer> numbers = Arrays.asList(10, 15, 20, 25, 30);

numbers.stream()
       .filter(n -> n % 2 == 0)
       .forEach(System.out::println);

Output

10
20
30

Odd Numbers

Java

numbers.stream()
       .filter(n -> n % 2 != 0)
       .forEach(System.out::println);

Output

15
25

Names Starting with A

Java

List<String> names = Arrays.asList("Alice", "Bob", "Alex", "David");

names.stream()
     .filter(name -> name.startsWith("A"))
     .forEach(System.out::println);

Output

Alice
Alex

Age Greater Than 25

Java

class Employee {
    String name;
    int age;

    Employee(String name, int age) {
        this.name = name;
        this.age = age;
    }
}

List<Employee> employees = Arrays.asList(
        new Employee("John", 22),
        new Employee("David", 28),
        new Employee("Alex", 35)
);

employees.stream()
         .filter(e -> e.age > 25)
         .forEach(e -> System.out.println(e.name));

Output

David
Alex

#Multiple Filters

Java

employees.stream()
         .filter(e -> e.age > 25)
         .filter(e -> e.name.startsWith("A"))
         .forEach(e -> System.out.println(e.name));

Output

Alex

Employee

Age > 25

Name starts with A

Result

#findFirst()

Returns the first element matching the condition. Return type: Optional<T>.

Java

Optional<Integer> number = numbers.stream()
        .filter(n -> n > 10)
        .findFirst();

System.out.println(number.get());

Output

Why Optional?

Java

numbers.stream()
       .filter(n -> n > 100)
       .findFirst();

No result exists. Instead of returning null, Java returns Optional.empty(). Safe usage:

Java

numbers.stream()
       .filter(n -> n > 100)
       .findFirst()
       .ifPresent(System.out::println);

#findAny()

Returns any matching element.

Java

numbers.stream()
       .filter(n -> n > 10)
       .findAny();

Sequential streams usually return the first match. Parallel streams may return any matching element.

findFirst() vs findAny()

findFirst()	findAny()
Preserves encounter order	May return any matching element
Good for ordered streams	Good for parallel streams
Usually slightly slower in parallel	Can be faster in parallel

#Match Operations

anyMatch()

Checks if at least one element matches. Returns boolean.

Java

boolean result = numbers.stream()
        .anyMatch(n -> n > 20);

System.out.println(result);

Output

true

allMatch()

Checks whether every element satisfies the condition.

Java

numbers.stream().allMatch(n -> n > 0);        // true
numbers.stream().allMatch(n -> n % 2 == 0);   // false

noneMatch()

Returns true only if no elements satisfy the condition.

Java

numbers.stream().noneMatch(n -> n < 0);   // true
numbers.stream().noneMatch(n -> n > 20);  // false

Difference Between Match Operations

Java

List<Integer> list = Arrays.asList(2, 4, 6, 7);

Operation	Code	Result	Why
`anyMatch()`	`list.stream().anyMatch(n -> n % 2 != 0)`	`true`	One odd number exists
`allMatch()`	`list.stream().allMatch(n -> n % 2 == 0)`	`false`	Not every number is even
`noneMatch()`	`list.stream().noneMatch(n -> n < 0)`	`true`	There are no negative numbers

#Short-Circuiting

These operations stop as soon as the result is known: findFirst(), findAny(), anyMatch(), allMatch(), noneMatch().

Java

List<Integer> list = Arrays.asList(2, 4, 6, 8, 9, 10);

boolean result = list.stream()
        .peek(System.out::println)
        .anyMatch(n -> n % 2 != 0);

System.out.println(result);

Output

2
4
6
8
9
true

Notice 10 is never processed because the answer is already known after finding 9.

#Real Spring Boot Examples

Java

// Validate user exists
boolean exists = users.stream()
        .anyMatch(u -> u.getEmail().equals(email));

// Get first active user
User user = users.stream()
        .filter(User::isActive)
        .findFirst()
        .orElseThrow();

// Check all orders are paid
boolean paid = orders.stream()
        .allMatch(Order::isPaid);

// Ensure no expired tokens
boolean valid = tokens.stream()
        .noneMatch(Token::isExpired);

#Interview Questions

Q1Is filter() an intermediate or terminal operation?

Intermediate.

Q2What is the return type of findFirst()?

Optional<T>.

Q3Why does findFirst() return Optional?

Because there may not be a matching element, and Optional avoids returning null and helps prevent NullPointerException.

Q4Which operations are short-circuiting?

findFirst(), findAny(), anyMatch(), allMatch() and noneMatch() (and limit() among intermediate operations).

Q5Difference between filter() and anyMatch()?

filter()	anyMatch()
Returns a `Stream<T>`	Returns `boolean`
Continues processing until a terminal operation	Stops as soon as one match is found
Used to filter a stream	Used to answer a yes/no question

#Practice Problems

Java

List<Integer> numbers = Arrays.asList(12, 5, 8, 19, 22, 31, 44, 50);

Print all even numbers.
Print all odd numbers.
Print numbers greater than 20.
Print numbers divisible by 4.
Find the first number greater than 20.
Find any even number.
Check if any number is greater than 100.
Check if all numbers are positive.
Check if none of the numbers are negative.
Count how many even numbers are present.

Coding Challenge (Interview Level)

Java

class Employee {
    int id;
    String name;
    String department;
    int age;
    double salary;
}

Find the first employee whose salary is greater than 100000.
Check whether any employee belongs to the "HR" department.
Check whether all employees are older than 18.
Check whether none of the employees have a negative salary.
Print employees whose names start with "A" and whose salary is greater than 50000.

#Chapter Summary

filter() and Predicate
Chaining multiple filters
findFirst() vs findAny() and why they return Optional
anyMatch(), allMatch(), noneMatch()
Short-circuiting
Spring Boot usage