1Z0-819 Modular Development & Deployment Practices

Question 1

What feature was introduced in Java 9 to support modular development?

Accepted Answer

Modules

Answer

Java 9 introduced the Java Platform Module System (JPMS), often referred to as Project Jigsaw, as a major feature to support modular development. This system allows developers to organize code into distinct, self-contained modules, improving encapsulation, reliability, and maintainability of large applications. It also enables the creation of smaller, custom runtime images.

Question 2

Which file defines a module in Java?

Accepted Answer

module-info.java

Answer

In the Java Platform Module System, a module is formally defined by a `module-info.java` file. This file, located at the root of the module's source directory, contains declarations such as the module's name, its dependencies on other modules (`requires`), and the packages it makes available to other modules (`exports`). It serves as the module descriptor.

Question 3

What keyword is used to declare a module requirement?

Accepted Answer

requires

Answer

The `requires` keyword is used within a `module-info.java` file to declare a dependency on another module. This explicitly states that the current module needs the functionality (exported packages) provided by the required module to compile and run correctly. This mechanism enforces strong encapsulation and explicit dependencies between modules.

Question 4

What does the 'exports' keyword do in module-info.java?

Accepted Answer

Exposes packages to other modules

Answer

In a `module-info.java` file, the `exports` keyword is used to specify which packages within the current module are accessible to other modules. By default, all packages inside a module are strongly encapsulated and not visible externally. `exports` explicitly opens up selected packages, allowing other modules to use their public types, thereby controlling the module's public API.

Question 5

What is jlink used for?

Accepted Answer

To create a custom Java runtime image

Answer

`jlink` is a command-line tool introduced in Java 9 that allows developers to create a custom, minimal Java runtime image. This image contains only the Java modules required by a specific application, significantly reducing the size of the runtime environment. This is particularly beneficial for deploying self-contained applications with a smaller footprint.

(1Z0-819) Oracle Java SE 11 Developer Practice Test

(1Z0-819) Oracle Java SE 11 Developer Practice Test

1Z0-819 Modular Development & Deployment Practices