OCP Java Platform Module System Questions and Answers

Question 1

A module named `com.app.main` requires a dependency on the `java.sql` module and needs to make its `com.app.ui` package available for other modules to use.
Which of the following `module-info.java` files correctly declares these requirements?

Accepted Answer

module com.app.main {
    requires java.sql;
    exports com.app.ui;
}

Answer

module com.app.main {
    imports java.sql;
    exports com.app.ui;
}

Answer

module com.app.main {
    requires java.sql;
    opens com.app.ui;
}

Answer

module com.app.main {
    needs java.sql;
    provides com.app.ui;
}

Question 2

Consider the following module declarations:

```java
// In module com.api
module com.api {
    exports com.api.data;
}

// In module com.service
module com.service {
    exports com.service.util; // This package contains types from com.api.data in its public method signatures
    requires com.api;
}

// In module com.client
module com.client {
    requires com.service;
    // Code here that uses com.service.util fails to compile
}
```
The code in `com.client` fails to compile because it cannot access types from `com.api.data` that are returned by methods in `com.service.util`. What is the best way to fix this issue?

Accepted Answer

In `com.service`'s module-info, change `requires com.api;` to `requires transitive com.api;`.

Answer

In `com.client`'s module-info, add `requires com.api;`.

Answer

In `com.api`'s module-info, change `exports com.api.data;` to `exports com.api.data to com.client;`.

Answer

In `com.service`'s module-info, add `exports com.api.data;`.

Question 3

A legacy JAR file named `legacy-utils.jar`, which does not contain a `module-info.class` descriptor, is placed on the module path at runtime. How will the Java Platform Module System treat this JAR?

Accepted Answer

It will be treated as an 'automatic module' with a name derived from the JAR file, and it will export all of its packages.

Answer

The application will fail to start because a JAR on the module path must contain a `module-info.class`.

Answer

It will be part of the 'unnamed module' and its packages will be available to all other modules.

Answer

It will be ignored by the module system, and its classes will be unavailable.

Question 4

A developer is building an application that uses a service provider interface. The module `com.app.drawing.api` defines the interface `com.app.drawing.api.Shape`. The module `com.app.drawing.impl` provides an implementation named `com.app.drawing.impl.Circle`. Which set of module directives correctly sets up the service relationship for discovery via `ServiceLoader`?

Accepted Answer

In `com.app.drawing.api`: `exports com.app.drawing.api;`
In `com.app.drawing.impl`: `requires com.app.drawing.api; provides com.app.drawing.api.Shape with com.app.drawing.impl.Circle;`

Answer

In `com.app.drawing.api`: `uses com.app.drawing.api.Shape;`
In `com.app.drawing.impl`: `provides com.app.drawing.api.Shape with com.app.drawing.impl.Circle;`

Answer

In `com.app.drawing.api`: `exports com.app.drawing.api;`
In `com.app.drawing.impl`: `requires com.app.drawing.api; exports com.app.drawing.impl;`

Answer

In `com.app.drawing.api`: `provides com.app.drawing.api.Shape;`
In `com.app.drawing.impl`: `uses com.app.drawing.api.Shape with com.app.drawing.impl.Circle;`

Question 5

A module `com.framework` needs to use reflection at runtime to access all members, including private fields and methods, of classes within the `com.app.model` package from the `com.app` module. The framework does NOT need to compile against any types in `com.app.model`. Which directive in `com.app`'s `module-info.java` provides the necessary access while adhering to the principle of least privilege?

Accepted Answer

`opens com.app.model to com.framework;`

Answer

`exports com.app.model to com.framework;`

Answer

`opens com.app.model;`

Answer

`exports com.app.model;`

Question 6

An application is launched with `app.jar` on the module path and a required `lib.jar` on the classpath. The module within `app.jar` does not have any special command-line flags applied. What is the expected outcome at runtime when code in `app.jar` attempts to access a class from `lib.jar`?

Accepted Answer

The access will fail with a `NoClassDefFoundError` or similar error.

Answer

The access will succeed, as the classpath content is automatically available to all modules.

Answer

The access will succeed, but the JVM will issue a warning about an 'unnamed module' being accessed.

Answer

The access will succeed only if `lib.jar` is also an automatic module.

A module named `com.app.main` requires a dependency on the `java.sql` module and needs to make its `com.app.ui` package available for other modules to use.Which of the following `module-info.java` files correctly declares these requirements?

A module named `com.app.main` requires a dependency on the `java.sql` module and needs to make its `com.app.ui` package available for other modules to use.
Which of the following `module-info.java` files correctly declares these requirements?