Core Built-In Functional Interfaces: Predicate, Function, Consumer, Supplier0%

Lambda Expression Syntax, Scope, and Variable Capture

Core Built-In Functional Interfaces: Predicate, Function, Consumer, Supplier

Advanced16 min read•Updated: 2025-01-15

🧩 Core Built-In Functional Interfaces: Predicate, Function, Consumer, Supplier

Introduction

Instead of forcing developers to declare custom interfaces for common functional signatures, Java provides the java.util.function package. This package provides standardized functional interfaces covering 95% of software transformation requirements.

🏛️ The "Big Four" Core Functional Interfaces

Interface	Method Signature	Conceptual Role	Example Real-World Use Case
`Predicate<T>`	`boolean test(T t)`	Evaluates a condition (true/false)	Filtering products by price > ₹500
`Function<T, R>`	`R apply(T t)`	Transforms input type `T` into result type `R`	Converting `Student` object into GPA `Double`
`Consumer<T>`	`void accept(T t)`	Consumes data, performs action, returns void	Printing logs or saving record to database
`Supplier<T>`	`T get()`	Produces/supplies data with zero inputs	Generating unique UUIDs or timestamps

💻 Practical Code Demonstrations

Visual Architecture & Process Flow

How data and code flow step-by-step

Flowchart

Step 1

Predicate<Double> isSolvent = balance

Step 2

balance >= 1000.0;

🔗 Chaining Functional Interfaces

Many functional interfaces provide default methods for composition:

Predicate: .and(), .or(), .negate()
Function: .andThen(), .compose()
Consumer: .andThen()

1Predicate<String> hasAtSymbol = s -> s.contains("@");
2Predicate<String> hasDot = s -> s.contains(".");
3Predicate<String> isValidEmail = hasAtSymbol.and(hasDot);
4 
5System.out.println(isValidEmail.test("admin@mskinstitute.in")); // true

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Lambda Expression Syntax, Scope, and Variable Capture

Core Built-In Functional Interfaces: Predicate, Function, Consumer, Supplier

Advanced16 min read•Updated: 2025-01-15

Study Materials

🧩 Core Built-In Functional Interfaces: Predicate, Function, Consumer, Supplier

Introduction

🏛️ The "Big Four" Core Functional Interfaces

Interface	Method Signature	Conceptual Role	Example Real-World Use Case
`Predicate<T>`	`boolean test(T t)`	Evaluates a condition (true/false)	Filtering products by price > ₹500
`Function<T, R>`	`R apply(T t)`	Transforms input type `T` into result type `R`	Converting `Student` object into GPA `Double`
`Consumer<T>`	`void accept(T t)`	Consumes data, performs action, returns void	Printing logs or saving record to database
`Supplier<T>`	`T get()`	Produces/supplies data with zero inputs	Generating unique UUIDs or timestamps

💻 Practical Code Demonstrations

Visual Architecture & Process Flow

How data and code flow step-by-step

Flowchart

Step 1

Predicate<Double> isSolvent = balance

Step 2

balance >= 1000.0;

🔗 Chaining Functional Interfaces

Many functional interfaces provide default methods for composition:

Predicate: .and(), .or(), .negate()
Function: .andThen(), .compose()
Consumer: .andThen()

1Predicate<String> hasAtSymbol = s -> s.contains("@");
2Predicate<String> hasDot = s -> s.contains(".");
3Predicate<String> isValidEmail = hasAtSymbol.and(hasDot);
4 
5System.out.println(isValidEmail.test("admin@mskinstitute.in")); // true

Next Lesson

Lambda Expression Syntax, Scope, and Variable Capture

Continue learning with hands-on practice, examples, and exercises in the upcoming topic.

Related Lessons

Previous Lesson	Next Lesson
Functional Interfaces & the @FunctionalInterface Annotation	Lambda Expression Syntax, Scope, and Variable Capture

Practice Quiz

Test your understanding of this lesson with 1 questions. Each question has one correct answer.

Previous Next