Java 8 Lambda Expressions

External

• Lambda Expressions Tutorial https://docs.oracle.com/javase/tutorial/java/javaOO/lambdaexpressions.html

Internal

• Java
• Closures

Overview

Java 8 introduces functional programming features, in form of lambda expressions. Lambda expressions allow for behavior parameterization.

Behavior Parameterization

Prior to Java 8, behavior parameterization was possible with anonymous classes.

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To Process

A lambda expression can be thought of as an anonymous methods. As shown in the "Syntax" section below, a lambda expression looks a lot like a method declaration.

TODO: one pass yellow/de-yellow over the Oracle tutorial.

Playground Example

https://github.com/NovaOrdis/playground/blob/master/java/java8/lambda-expression/src/main/java/io/novaordis/playground/java/java8/lambda/Main.java

Functional Interface

An interface with only one method is named functional interface

Apparently this is the type of a lambda expression, it describe the function signature.

The Type of a Lambda Expression

Elaborate here.

Syntax

A lambda expression consists in a comma-separated list of formal parameters, enclosed in parentheses, followed by the arrow token "->" followed by a body, which may be a single expression or a statement block.

(comma_separated_formal_parameter_list) -> body

Formal Parameters

The type of the parameters may be omitted.

If there is a single parameter, the enclosed parentheses may be omitted.

Body

The body may be a single expression, or a statement block.

Method References

Example:

    public ZipHandler getZipHandler() {

        return ZipUtil::getTopLevelDirectoryName;
    }

Variables

The variables used in the lambda expressions must be final.

Statement Lambdas and Expression Lambdas

Statement Lambda:

(ZipEntry e) -> {  s.append(e.getName()); }

Expression Lambda:

(ZipEntry e) -> s.append(e.getName())