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This flashcard set covers advanced Java programming concepts, focusing on exceptions, streams, and concurrent programming. It delves into methods, classes, and interfaces, explaining how to handle exceptions, work with streams, and manage objects. The set is particularly useful for developers preparing for a Java certification exam, as it provides detailed insights into Java's exception handling, stream operations, and concurrent programming techniques.

Cartes-fiches

Utilisateurs

Langue

Anglais

Catégorie

Informatique

Niveau

Autres

Créé / Mis à jour

02.05.2019 / 03.05.2019

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What rules apply to the catch clauses?

It is ilegal to declare a subclass exception in a chatch block that is lower down in the list than a superclass
you cannot catch a checked exception type that cannot potentially be thrown by the try clause

What happens if an exception is thrown in a try-with-resource statmement?

It depends on how the try block endend:

Try-block ended normally: The exception from the close method is thrown and must either be handeled in a catch block or by the caller (checked exceptions must be declared, of course)
Try-block ended with an exception: The exception from the close method is added as a suppressed exception to the one from the try-block.

What does this code do?
public void rerhrowing() throws SQLException, DateTimeParseException {
try {
    parseData();
} catch (Exception e) {
    System.err.println(e);
    throw e;
}
}

It is a short for the following code to prevent duplicates. Java can infer the specific Exception from the method signature

public void rerhrowing() throws SQLException, DateTimeParseException {
try {
    parseData();
} catch (SQLException | DateTimeParseException e) {
    System.err.println(e);
    throw e;
}
}

Is IllegalFormatException a checked exception?

What has to be minded when using the Thread.sleep method?

It declares the checked InterruptedException which must be handeled

What is important when using the ExecutorService class?

It is important to call the shutdown() method. A thread executor creates a non-demon thread on the first task that is executed, so failing to call shutdown will result in you application never terminating.

What is the difference between Runnable and Callable

Callable can return a value and allows a throws declaration of Exception

@FunctionalInterface Callable<V> { V call() throws Exception;}

@FunctionalInterface Runnable { void run()}

What common tools does java offer to prevent race conditions?

Monitor using the synchronized keyword = Locking
Atomic clases that provide atomic operations

What is the difference between a BlockingQueue/BlockingDeque and "normal" Queue/Deque?

The Blocking versions offer additional methods that will wait for a specific amount of time to complete an operation:

eg. boolean offer(E e, long timeout, TimeUnit unit) throws InterruptedException -> Returns false on timeout

eg. E poll(long timeout, TimeUnit unit) throws InterruptedException -> Returns null on timeout

What is the main difference betwen a serial stream an a parallel stream?

Seria streams are ordered whereas parallel streams are not necessarily

What are the three steps of the fork/join framework?

Create a ForkJoinTask
- ForkJoinTask<?> task = new MyActionOrTask(...);
Create the ForkJoinPool
- ForkJoinPool pool = new ForkJoinPool();
Start the ForkJoinTask
- pool.invoke(action)
- Object result = pool.invoke(task);

Do ExecutorService.submit and ExecutorService.execute throw a checked exception

How can you convert an INputStream into a Reader

By wrapping it with a InputStreamReader

What are PrintStream and PrintWriter for?

They write formatted representations of Java objects to a binary stream

Is the int parameter for the InputSTream.mark() method required?

Yes

How can you determine EOF when using a FileReader?

When the readLine() method returns null or or read() returns -1

How can you determine EOF when using a ObjectInputStream?

Catch the EOFException!

is it safe to use inputsream.available() to check if a stream is EOF?

NO! Use the specific strategies for each kind of stream

How is a serialized object created?

Java calls the first non-arg constructor for the first nonserializable parent class, skipping the constructors of all serialized classes in between!
Static variables are ignored
default intializers (eg private String myField = "123" and {}) are ignored

What is special about the print, println, printf and format methods found on the PrintStream/PrintWriter classes?

They do not throw an exception! The checkError() method can be used for that instead

Does DateTimeFormatter throw a Checked Exception or an uncheced?

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It throws a DateTimeException which is a RuntimeException

Is it dangerous to ommit the generic type when using Predicate or Function?

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Yes:

Compiler Warning
Auto Boxing might not work as Expected, eg. boolean will neither be autoboxed into a Boolean nor Object!

Does forEach accept an implementation of Function?

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No, only a Consumer implementation!

What happens when catching an checked exception that is not declared by any method in the try block?

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The code will not compile!

Can you declare a Method as final?

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Yes, instance methods, but not static methods!

Must a ENUM enumeration end with a Semicolon?

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The semicolon is only required when methods/constructors are declared afterwards!

What is the difference between Optional.orElse(...) and Optional.orElseGet(...)?

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Optional.orElse(T) returns the provided value
Optional.orElseGet(Supplier<? extends T>) uses the provided supplier to get the default value

Can a Properties Class be instantiated using a Constructor?

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Yes

Is InputStream an Interrface?

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No, it's an abstract class!

Is Writer an Interface?

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No, its an abstract class

How big is a short?

2 Bytes

When does isSameFile return true?

when p1.equals(p2) -> true
when on different FS -> false
when the same file: true
- including symlinks
- may require to open or access both files

Does instant have a plus method?

Yes, but it only supports units of DAYS or smaller!

Is a Patho object immutable?

Yes! Same as with the new DateTime API

When having an updatable result set and calling a updateXX method, are the changes applied immediately?

No, updateRow must be called before the changes are applied on the DB.

Will two objects that return true for equals() will always return 0 when passed to compareTo()?

Multiple comparators can use different orders for comparison, which do not need to match the definition of equality

Do the compare() and compareTo() methods have the same contract for the return value?

Yes

try{...}catch(Error e){throw e;}

Do you have to handle Error?

Is this assert statement valid?

assert x==y : new StringBuilder("Crap")

Yes, the message can be anything but void

Is this a valid boolean declaration?

.123?

Yes

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Cartes-fiches

is it safe to use inputsream.available() to check if a stream is EOF?

NO! Use the specific strategies for each kind of stream

How is a serialized object created?

Java calls the first non-arg constructor for the first nonserializable parent class, skipping the constructors of all serialized classes in between!
Static variables are ignored
default intializers (eg private String myField = "123" and {}) are ignored