Course Content

Stream API

1. Fundamentals and Functional Capabilities of Stream API

Architecture Principles What Is a Functional Interface?Predicate: Data Filtering Challenge: Filtering Corporate Email Addresses Function: Data Transformation Challenge: Income Tax Calculation Comparable: Natural Ordering of Data Comparator: Custom Comparison of Data Challenge: Sorting Employees Consumer: Processing Data Supplier: Data Generation Bi-versions of Functional Interfaces Challenge: Filtering Users by Two Criteria BinaryOperator: Combining Two Values

2. Intermediate Operations in Stream API

Transforming Elements with the map() Method Filtering Elements with the filter() Method Challenge: Factory Product Filtering Working with Nested Structures with the flatMap() Method Arranging Items in Order with the sorted() Method Challenge: Selecting the Best Cars on the Production Line Eliminating Duplicates with the distinct() Method Challenge: Factory Quality Control Restricting and Skipping Elements with the limit() and skip() Methods Challenge: Finding the Top 3 Hardest-Working Employees Intermediate Processing with the peek() Method

3. Terminal Operations in the Stream API

collect() Gathering Stream Elements into a Collection Challenge: Build a Custom Collector for Category Counting Collectors Utility Class for Stream API Processing Elements with the forEach() Method Handling Values with the Optional Class Aggregating Elements with the reduce() Method Challenge: Calculating Total Cost with Discounts and Tax Calculating Stream Statistics with count(), max(), and min()Retrieving Stream Summary Metrics with summaryStatistics() Method Retrieving Elements from a Stream with findFirst() and findAny()Challenge: Selecting Random Products Within a Category Checking Stream Elements Against a Condition with allMatch()Challenge: Ensuring Fast Delivery for Expensive Products

4. Practical Applications of Stream API

Real-World Examples of Using Stream API Performance in Stream API Exception Handling in Stream API Summary

BinaryOperator: Combining Two Values

This interface is particularly useful when combining two values of the same type, such as performing mathematical calculations or merging data.

The BinaryOperator<T> interface extends BiFunction<T, T, T>, but unlike BiFunction, both input arguments and the return value must always be of the same type T.

Its only abstract method, apply(T t1, T t2), executes an operation on two arguments and returns the result.

Practical Example

Let's say you have a payroll system where you need to determine which of two bonuses — annual or quarterly — is higher so that the larger amount can be awarded to an employee.

Main


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package com.example;

import java.util.function.BinaryOperator;

public class Main {
    public static void main(String[] args) {
        BinaryOperator<Double> maxBonus = (bonus1, bonus2) -> Math.max(bonus1, bonus2);

        double annualBonus = 5000.0;
        double quarterlyBonus = 1500.0;

        double finalBonus = maxBonus.apply(annualBonus, quarterlyBonus);
        System.out.println("Awarded Bonus: " + finalBonus);
    }
}

In this example, you create a BinaryOperator<Double> that utilizes Math.max() to compare two values and return the larger one.

You then define two bonuses: annualBonus (annual bonus) and quarterlyBonus (quarterly bonus).

The apply() method is called to determine the higher bonus, and the result is printed to the console. This approach is useful when you need to dynamically select the best option without complex conditional logic.

Static Methods

In addition to its primary apply() method, BinaryOperator<T> includes several useful static methods:

maxBy(Comparator<T> comparator) – returns a BinaryOperator<T> that selects the greater of two values based on the provided Comparator<T>;
minBy(Comparator<T> comparator) – returns a BinaryOperator<T> that selects the smaller of two values based on the provided Comparator<T>.

Example Usage

Let's say you have an employee management system where you need to determine which of two candidates has a higher rating in order to select the best one for a promotion.

Main


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package com.example;

import java.util.Comparator;
import java.util.function.BinaryOperator;

public class Main {
    public static void main(String[] args) {
        BinaryOperator<Employee> topPerformer =
                BinaryOperator.maxBy(Comparator.comparingInt(Employee::getRating));

        Employee employee1 = new Employee("John", 85);
        Employee employee2 = new Employee("Sarah", 90);

        Employee bestEmployee = topPerformer.apply(employee1, employee2);
        System.out.println("Top employee: " + bestEmployee.getName());
    }
}

class Employee {
    private String name;
    private int rating;

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

    public String getName() {
        return name;
    }

    public int getRating() {
        return rating;
    }
}

The BinaryOperator.maxBy() method takes a Comparator<Employee>, which uses Employee::getRating to compare employees by their ratings.

Two Employee objects are then created with different ratings. The apply() method selects the employee with the highest rating and prints their name.

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Section 1. Chapter 15

Stream API

BinaryOperator: Combining Two Values

Practical Example

Static Methods

Example Usage

1. What is the main purpose of the `BinaryOperator<T>` functional interface?

2. What is the primary method in the `BinaryOperator<T>` interface?

3. Which interface is the parent of `BinaryOperator<T>`?

4. What will the following code output?

Stream API

BinaryOperator: Combining Two Values

Practical Example

Static Methods

Example Usage

1. What is the main purpose of the BinaryOperator<T> functional interface?

2. What is the primary method in the BinaryOperator<T> interface?

3. Which interface is the parent of BinaryOperator<T>?

4. What will the following code output?

1. What is the main purpose of the `BinaryOperator<T>` functional interface?

2. What is the primary method in the `BinaryOperator<T>` interface?

3. Which interface is the parent of `BinaryOperator<T>`?