Java Developer OCA Questions Flashcards
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Questions and Answers

It can be extended by another interface.

False

Tell me about the keyword implements.

The keyword implements is used when a class inherits method prototypes from an interface.

Which logical operators are known as 'short circuiting logical operators'?

|| and &&

By default (i.e. no modifier) the member is only accessible to classes in the same package and subclasses of the class.

<p>False</p> Signup and view all the answers

You cannot specify visibility of local variables.

<p>True</p> Signup and view all the answers

Local variables always have default accessibility.

<p>False</p> Signup and view all the answers

Local variables can be declared as private.

<p>False</p> Signup and view all the answers

Local variables can only be declared as public.

<p>False</p> Signup and view all the answers

A functional interface has exactly one method and it must be abstract.

<p>False</p> Signup and view all the answers

A functional interface has exactly one method and it may or may not be abstract.

<p>False</p> Signup and view all the answers

A functional interface must have exactly one abstract method and may have other default or static methods.

<p>True</p> Signup and view all the answers

A functional interface must have exactly one static method and may have other default or abstract methods.

<p>False</p> Signup and view all the answers

The 'default' constructor is provided by the compiler only if the class and any of its super classes does not define any constructor.

<p>False</p> Signup and view all the answers

The 'default' constructor takes no arguments.

<p>True</p> Signup and view all the answers

A default constructor is used to return a default value.

<p>False</p> Signup and view all the answers

To define a default constructor, you must use the default keyword.

<p>False</p> Signup and view all the answers

The 'default' constructor is always public.

<p>False</p> Signup and view all the answers

Using a continue in a while loop causes the loop to break the current iteration and start the next iteration of the loop.

<p>True</p> Signup and view all the answers

A character literal can be used as a value for a case label.

<p>True</p> Signup and view all the answers

A 'long' cannot be used as a switch variable.

<p>True</p> Signup and view all the answers

An empty switch block is a valid construct.

<p>True</p> Signup and view all the answers

A switch block must have a default label.

<p>False</p> Signup and view all the answers

If present, the default label must be the last of all the labels.

<p>False</p> Signup and view all the answers

What is java.util.function.Predicate?

<p>It is an interface that has only one abstract method with the signature public boolean test(T t).</p> Signup and view all the answers

A method with no access modifier defined in a class can be overridden by a method marked protected in the subclass.

<p>True</p> Signup and view all the answers

Using a break in a while loop causes the loop to break the current iteration and start the next iteration of the loop.

<p>False</p> Signup and view all the answers

What class of objects can be declared by the throws clause?

<p>All of the above</p> Signup and view all the answers

Tell me something about scope.

<p>Class level means static fields that can be accessed anywhere in the class; instance level means instance fields accessible only from instance methods.</p> Signup and view all the answers

Which class should you use to represent just a date without any timezone information?

<p>java.time.LocalDate</p> Signup and view all the answers

A try statement must always have a ________ associated with it.

<p>catch, finally or both</p> Signup and view all the answers

Does the String class have a reverse method?

<p>False</p> Signup and view all the answers

Tell me something about fields in an interface.

<p>Fields in an interface are implicitly public, static, and final.</p> Signup and view all the answers

What happens when you call System.exit(0) in a try block followed by a finally block?

<p>The JVM exits, so the finally block will not execute.</p> Signup and view all the answers

What are the primitive data types?

<p>boolean, byte, short, char, int, long, float, and double.</p> Signup and view all the answers

What is the correct declaration for an abstract method 'add' that takes no arguments and returns nothing?

<p>abstract public void add() throws Exception;</p> Signup and view all the answers

What does the zeroth element of the string array passed to the standard main method contain?

<p>The first argument of the argument list, if present.</p> Signup and view all the answers

Which exception should a Java programmer throw explicitly?

<p>Exception</p> Signup and view all the answers

Identify the valid members of Boolean class.

<p>valueOf(boolean)</p> Signup and view all the answers

An abstract class can be extended by an abstract or a concrete class.

<p>True</p> Signup and view all the answers

An abstract class cannot implement an interface.

<p>False</p> Signup and view all the answers

A concrete class can be extended by an abstract or a concrete class.

<p>True</p> Signup and view all the answers

An interface can be extended by another interface.

<p>True</p> Signup and view all the answers

An interface can be extended by an abstract class.

<p>False</p> Signup and view all the answers

The modulus operator % can only be used with integer operands.

<p>False</p> Signup and view all the answers

The arithmetic operators *, / and % have the same level of precedence.

<p>True</p> Signup and view all the answers

&& can have integer as well as boolean operands.

<p>False</p> Signup and view all the answers

~ can have integer as well as boolean operands.

<p>False</p> Signup and view all the answers

How many times can the keyword 'package' appear in a Java source file?

<p>Once.</p> Signup and view all the answers

LocalDate, LocalTime, and LocalDateTime extend Date.

<p>False</p> Signup and view all the answers

LocalDate, LocalTime, and LocalDateTime implement TemporalAccessor.

<p>True</p> Signup and view all the answers

Both LocalDate and LocalTime extend LocalDateTime, which extends java.util.Date.

<p>False</p> Signup and view all the answers

LocalDate, LocalTime, and LocalDateTime implement TemporalAccessor and extend java.util.Date.

<p>False</p> Signup and view all the answers

What is the correct order of restrictiveness for access modifiers?

<p>public, protected, package (no modifier), private</p> Signup and view all the answers

Are private members inherited?

<p>False</p> Signup and view all the answers

What can be the type of a catch argument?

<p>Any class that is a Throwable.</p> Signup and view all the answers

If a RuntimeException is not caught, the method will terminate and normal execution of the thread will resume.

<p>False</p> Signup and view all the answers

An overriding method must declare that it throws the same exception classes as the method it overrides.

<p>False</p> Signup and view all the answers

The main method of a program can declare that it throws checked exceptions.

<p>False</p> Signup and view all the answers

A method declaring that it throws a certain exception class may throw instances of any subclass of that exception class.

<p>True</p> Signup and view all the answers

Finally blocks are executed if and only if an exception gets thrown while inside the corresponding try block.

<p>False</p> Signup and view all the answers

Tell me more about how exceptions are handled.

<p>If an exception is uncaught, it propagates up the call stack until handled or terminates the thread.</p> Signup and view all the answers

Is it possible to create arrays of length zero?

<p>False</p> Signup and view all the answers

The 'default' constructor is provided by the compiler only if the class does not define any constructor.

<p>True</p> Signup and view all the answers

The 'default' constructor initializes the instance members of the class.

<p>False</p> Signup and view all the answers

The 'default' constructor calls the no-args constructor of the super class.

<p>True</p> Signup and view all the answers

The 'default' constructor initializes instance as well as class fields of the class.

<p>False</p> Signup and view all the answers

The 'default' constructor is provided by the compiler if the class does not define a 'no-args' constructor.

<p>False</p> Signup and view all the answers

The private keyword can never be applied to a class.

<p>False</p> Signup and view all the answers

The synchronized keyword can never be applied to a class.

<p>True</p> Signup and view all the answers

The synchronized keyword may be applied to a non-primitive variable.

<p>False</p> Signup and view all the answers

The final keyword can never be applied to a class.

<p>False</p> Signup and view all the answers

A final variable can be hidden in a subclass.

<p>True</p> Signup and view all the answers

Tell me about the final keyword.

<p>The final keyword means that the class cannot be subclassed, the method cannot be overridden, and the variable is a constant.</p> Signup and view all the answers

How can you declare a method someMethod() such that an instance of the class is not needed to access it?

<p>all of the above</p> Signup and view all the answers

Is this a valid declaration in a class? abstract int absMethod(int param) throws Exception;

<p>False</p> Signup and view all the answers

Is this a valid declaration in a class? abstract native int absMethod(int param) throws Exception;

<p>False</p> Signup and view all the answers

Is this a valid declaration in a class? float native getVariance() throws Exception;

<p>False</p> Signup and view all the answers

Is this a valid declaration in a class? abstract private int absMethod(int param) throws Exception;

<p>False</p> Signup and view all the answers

Subclasses must define all the abstract methods that the superclass defines.

<p>False</p> Signup and view all the answers

A class implementing an interface must define all the methods of that interface.

<p>False</p> Signup and view all the answers

A class cannot override the superclass's constructor.

<p>True</p> Signup and view all the answers

It is possible for two classes to be the superclass of each other.

<p>False</p> Signup and view all the answers

An interface can implement multiple interfaces.

<p>False</p> Signup and view all the answers

List three classes that can be thrown using a throw statement.

<p>Exception</p> Signup and view all the answers

Private methods cannot be overridden in subclasses.

<p>True</p> Signup and view all the answers

A subclass can override any method in a non-final superclass.

<p>False</p> Signup and view all the answers

An overriding method can declare that it throws a wider spectrum of checked exceptions than the method it is overriding.

<p>False</p> Signup and view all the answers

The parameter list of an overriding method must be a subset of the parameter list of the method that it is overriding.

<p>False</p> Signup and view all the answers

The overriding method may opt not to declare any throws clause even if the original method has a throws clause.

<p>True</p> Signup and view all the answers

The extends keyword is used to specify inheritance.

<p>True</p> Signup and view all the answers

A subclass of a non-abstract class cannot be declared abstract.

<p>False</p> Signup and view all the answers

A subclass of an abstract class can be declared abstract.

<p>True</p> Signup and view all the answers

A subclass of a final class can be abstract.

<p>False</p> Signup and view all the answers

A class, in which all the members are declared private, cannot be declared public.

<p>False</p> Signup and view all the answers

An interface may extend an interface.

<p>True</p> Signup and view all the answers

An interface may extend a class and may implement an interface.

<p>False</p> Signup and view all the answers

A class can implement an interface and extend a class.

<p>True</p> Signup and view all the answers

A class can extend an interface and can implement a class.

<p>False</p> Signup and view all the answers

An interface can only be implemented and cannot be extended.

<p>False</p> Signup and view all the answers

Study Notes

Java Developer OCA Questions Overview

  • java.util.function.Predicate is a functional interface with a single abstract method public boolean test(T t), representing a condition for evaluating values.
  • Methods without access modifiers can be overridden in subclasses by protected methods, as protected access is more permissive.
  • The break statement in loops terminates the loop immediately; it does not initiate the next iteration.
  • The throws clause can declare any class that extends Throwable, including Exception, Error, and RuntimeException.
  • Scope defines the visibility of fields: class level fields (static) can be accessed anywhere in the class, while instance level fields can only be accessed by instance methods.
  • Use java.time.LocalDate to represent dates without time zones; it is recommended over the old java.util.Date class.
  • Every try statement must have either a catch, finally, or both associated with it.
  • The String class does not have a reverse method; however, StringBuffer and StringBuilder do.
  • Fields in an interface are implicitly public, static, and final, although declaring these keywords is not a good practice.
  • Calling System.exit(0) in a try block bypasses any finally block execution, as the JVM exits immediately.
  • Java primitive data types include boolean, byte, short, char, int, long, float, and double.
  • An abstract method declaration can be abstract public void add() throws Exception;, allowing it to be overridden by subclasses.

Exception Handling

  • The zeroth element in the main method's argument array contains the first argument passed; an empty array signifies no arguments were provided.
  • Exception is appropriate for use in a desktop application for known exceptional situations, unlike Error and RuntimeException, which are typically not thrown explicitly.
  • Valid members of the Boolean class include parseBoolean(String), valueOf(boolean), and the static member FALSE.
  • An abstract class can be extended by another abstract or concrete class, while it can also implement an interface.
  • Interfaces can extend other interfaces but are not allowed to be directly extended by classes; classes implement interfaces instead.

Operators and Access Modifiers

  • The modulus operator % can operate on both integer and floating-point numbers.
  • The & operator can accept both integral and boolean operands without short-circuiting, unlike &&.
  • Arithmetic operators *, /, and % share the same level of precedence in Java.
  • The order of access modifiers from least to most restrictive is public, protected, package-private (default), and private.
  • Private members of a class are not inherited by subclasses; only protected and public members are.
  • Catch argument types in exception handling can be any class extending Throwable.

Class and Interface Relationships

  • A class must define all abstract methods it inherits unless it is also declared abstract.
  • A class implementing an interface must fulfill all its method contracts unless declared abstract.
  • Constructors are not inherited, so a class cannot override super class constructors.
  • Local variables have no visibility modifiers, being accessible only within the block they are declared, and cannot be declared as public or private.
  • A functional interface is defined as having exactly one abstract method (may or may not be abstract in practice).

Additional Java Concepts

  • synchronized can be applied only to methods or blocks but not directly to classes.
  • The final keyword prevents a class from being subclassed, a method from being overridden, or a variable from being reassigned.
  • It is permissible to create zero-length arrays; for example, in the absence of command-line arguments passed to a Java application.
  • The implements keyword is used when a class declares that it conforms to the method structure of an interface.
  • Short-circuit logical operators in Java are || and &&, which may stop evaluation if the result is already determinable.### Functional Interfaces
  • A functional interface must have exactly one abstract method, but may have other default or static methods.
  • A functional interface does not require exactly one static method; it can have zero or more static methods.

Default Constructor

  • The default constructor is provided by the compiler if the class does not define any constructor, regardless of the parent class's constructors.
  • A default constructor is characterized by taking no arguments.
  • Constructors do not return values; their purpose is to initialize an object's state.
  • Defining a default constructor does not require using the keyword "default."
  • The access modifier of a default constructor matches the access modifier of the class it belongs to.

Control Flow in Loops

  • The continue statement in a while loop causes the current iteration to stop and begins the next iteration.
  • The continue statement skips the remaining lines in the loop for the current iteration and checks the loop's condition before continuing.

Switch Statement Characteristics

  • A character literal can be used as a case label in a switch statement.
  • Types such as boolean, long, float, and double are not valid as switch variables.
  • An empty switch block is syntactically valid.
  • A switch block does not require a default label; it can function without one.
  • The default label, if included, can appear in any order within the switch block.

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