Free Oracle 1z0-830 Practice Exam with Questions & Answers | Set: 3

The Java Platform Module System (JPMS), introduced in Java 9, modularizes the Java platform and applications. Understanding the behavior of named and unnamed modules is crucial.

B. The unnamed module exports all of its packages.

Correct. The unnamed module, which includes all code on the classpath, exports all of its packages. This means that any code can access the public types in these packages. However, the unnamed module cannot be explicitly required by named modules.

C. If a package is defined in both a named module and the unnamed module, then the package in the unnamed module is ignored.

Correct. In cases where a package is present in both a named module and the unnamed module, the version in the named module takes precedence. The package in the unnamed module is ignored to maintain module integrity and avoid conflicts.

F. If a request is made to load a type whose package is not defined in any known module, then the module system will attempt to load it from the classpath.

Correct. When the module system cannot find a requested type in any known module, it defaults to searching the classpath (i.e., the unnamed module) to locate the type.

Incorrect Options:

A. Code in an explicitly named module can access types in the unnamed module.

Incorrect. Named modules cannot access types in the unnamed module. The unnamed module can read from named modules, but the reverse is not allowed to ensure strong encapsulation.

D. We must add a module descriptor to make an application developed using a Java version prior to SE9 run on Java 11.

Incorrect. Adding a module descriptor (module-info.java) is not mandatory for applications developed before Java 9 to run on Java 11. Such applications can run in the unnamed module without modification.

E. The unnamed module can only access packages defined in the unnamed module.

Incorrect. The unnamed module can access all packages exported by all named modules, in addition to its own packages.

Understanding TreeMap.subMap(fromKey, fromInclusive, toKey, toInclusive)

TreeMap.subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) returns aportion of the mapthat falls within the specified key range.

Thefirst boolean parameter(fromInclusive) determines if the fromKey should be included.

Thesecond boolean parameter(toInclusive) determines if the toKey should be included.

Given TreeMap Contents

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{1=Moulin Rouge, 2=Crazy Horse, 3=Paradis Latin, 4=Le Lido, 5=Folies Bergère}

Applying subMap(2, true, 5, false)

Includeskey 2 ("Crazy Horse")✅(fromInclusive = true)

Includeskey 3 ("Paradis Latin")✅

Includeskey 4 ("Le Lido")✅

Excludes key 5 ("Folies Bergère")❌(toInclusive = false)

Final Output

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{2=Crazy Horse, 3=Paradis Latin, 4=Le Lido}

Thus, the correct answer is:✅{2=Crazy Horse, 3=Paradis Latin, 4=Le Lido}

References:

Java SE 21 - TreeMap.subMap()

Java SE 21 - NavigableMap

In this program, we have two classes, A and B, both implementing the Serializable interface, and a Test class with the main method.

Program Flow:

Serialization:

An instance of class A is created and assigned to the variable a.

An ObjectOutputStream is created to write to the file "o.ser".

The object a is serialized and written to the file.

The ObjectOutputStream is closed.

Deserialization:

An ObjectInputStream is created to read from the file "o.ser".

The program attempts to read an object from the file and cast it to an instance of class B.

The ObjectInputStream is closed.

Analysis:

Serialization Process:

The object a is an instance of class A and is serialized into the file "o.ser".

Deserialization Process:

When deserializing, the program reads the object from the file and attempts to cast it to class B.

However, the object in the file is of type A, not B.

Since A and B are distinct classes with no inheritance relationship, casting an A instance to B is invalid.

Exception Details:

Attempting to cast an object of type A to type B results in a ClassCastException.

The exception message would be similar to:

pgsql

Exception in thread "main" java.lang.ClassCastException: class A cannot be cast to class B

Conclusion:

The program compiles successfully but throws a ClassCastException at runtime when it attempts to cast the deserialized object to class B.

In Java, method overloading allows multiple methods with the same name to exist in a class, provided they have different parameter lists (i.e., different number or types of parameters). However, having two methods with the exact same parameter list and only differing in return type is not permitted.

In the provided code, the FetchService class contains two fetch methods:

public String fetch()

public LocalDate fetch()

Both methods have identical parameter lists (none) but differ in their return types (String and LocalDate, respectively). This leads to a compilation error because the Java compiler cannot distinguish between the two methods based solely on return type.

The Java Language Specification (JLS) states:

"It is a compile-time error to declare two methods with override-equivalent signatures in a class."

In this context, "override-equivalent" means that the methods have the same name and parameter types, regardless of their return types.

Therefore, the code will fail to compile due to the duplicate method signatures, and the correct answer is B: Compilation fails.

Understanding post++ (Post-increment)

post++uses the value first, then increments it.

postResult = post++ + 10;

post starts as 5.

post++ returns 5, then post is incremented to 6.

postResult = 5 + 10 = 15.

Final value of post after this line is 6.

Understanding ++pre (Pre-increment)

++preincrements the value first, then uses it.

preResult = ++pre + 10;

pre starts as 5.

++pre increments pre to 6, then returns 6.

preResult = 6 + 10 = 16.

Final value of pre after this line is 6.

Thus, the final output is:

yaml

postResult: 15, preResult: 16, Final value of post: 6, Final value of pre: 6

References:

Java SE 21 - Operators and Expressions

Java SE 21 - Arithmetic Operators