How to Filter an Array Using Java 8 Streams

In this guide, we will explore how to filter arrays using Java 8 Streams. Java Streams provide an efficient way to filter data based on conditions. We will demonstrate how to filter arrays of integers, strings, and custom objects using the Employee class for the custom object example.

1. Filtering an Integer Array

Let’s start by filtering an array of integers. We’ll filter out numbers less than or equal to 5 and keep only the numbers greater than 5.

Example

import java.util.Arrays;

public class IntegerArrayFilter {
    public static void main(String[] args) {
        // Define the input array of integers
        int[] intArray = {1, 6, 3, 9, 2, 7};

        // Use Java 8 Stream to filter numbers greater than 5
        int[] filteredArray = Arrays.stream(intArray)
                .filter(num -> num > 5)  // Filter numbers greater than 5
                .toArray();  // Convert back to an array

        // Display the filtered array
        System.out.println("Filtered Integer Array (numbers > 5): " + Arrays.toString(filteredArray));
    }
}

Output

Filtered Integer Array (numbers > 5): [6, 9, 7]

Explanation

• Arrays.stream(intArray) creates a stream from the integer array.
• The filter() method is used to filter numbers greater than 5.
• toArray() collects the filtered elements back into an array, which is then printed using Arrays.toString().

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2. Filtering a String Array

Next, let’s filter a string array. In this example, we’ll filter strings that start with the letter "J".

Example

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class StringArrayFilter {
    public static void main(String[] args) {
        // Define the input array of strings
        String[] stringArray = {"Java", "Python", "JavaScript", "C++", "Ruby"};

        // Use Java 8 Stream to filter strings that start with "J"
        List<String> filteredStrings = Arrays.stream(stringArray)
                .filter(str -> str.startsWith("J"))  // Filter strings starting with 'J'
                .collect(Collectors.toList());  // Collect the result into a list

        // Display the filtered list of strings
        System.out.println("Filtered String Array (starts with 'J'): " + filteredStrings);
    }
}

Output

Filtered String Array (starts with 'J'): [Java, JavaScript]

Explanation

• Arrays.stream(stringArray) converts the string array into a stream.
• The filter() method checks if the strings start with the letter "J".
• collect(Collectors.toList()) collects the filtered elements into a list, which is printed.

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3. Filtering a Custom Object Array (Using Employee Class)

Lastly, let’s filter an array of Employee objects based on their salary. We will filter employees who earn more than 50,000.

Example

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class EmployeeArrayFilter {
    public static void main(String[] args) {
        // Define the input array of Employee objects
        Employee[] employeeArray = {
                new Employee("John", 60000),
                new Employee("Alice", 45000),
                new Employee("Bob", 70000),
                new Employee("Jane", 48000)
        };

        // Use Java 8 Stream to filter Employee objects based on salary
        List<Employee> filteredEmployees = Arrays.stream(employeeArray)
                .filter(employee -> employee.getSalary() > 50000)  // Filter employees with salary > 50000
                .collect(Collectors.toList());  // Collect the result into a list

        // Display the filtered list of Employee objects
        System.out.println("Filtered Employees (salary > 50000): " + filteredEmployees);
    }
}

// Employee class definition
class Employee {
    private String name;
    private int salary;

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

    public int getSalary() {
        return salary;
    }

    @Override
    public String toString() {
        return name + " (" + salary + ")";
    }
}

Output

Filtered Employees (salary > 50000): [John (60000), Bob (70000)]

Explanation

• Arrays.stream(employeeArray) converts the employee array into a stream.
• The filter() method checks for employees with a salary greater than 50,000.
• collect(Collectors.toList()) collects the filtered employees into a list.
• The filtered list is printed using the toString() method of the Employee class.

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Conclusion

In Java 8, filtering arrays of different types—integers, strings, and custom objects like Employee—is made simple with the Stream API. By using the filter() method, you can easily specify conditions and process elements based on your requirements. Java Streams provide a clean and efficient way to handle filtering for various data types.