Java Methods and Classes Quiz

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Questions and Answers

What happens when two threads access the same ArrayList object simultaneously?

  • A ConcurrentModificationException is thrown (correct)
  • One thread accesses the object, causing the other to be blocked
  • Both threads can access the object without any issue
  • Both threads receive a Null Pointer exception

Which method in the Date class checks if a date occurs before a specified date?

  • isBefore()
  • precedes()
  • before() (correct)
  • compare()

Which class is used to associate a value with a String key in Java?

  • Properties (correct)
  • Map
  • Dictionary
  • Hashtable

What is the primary role of packages in Java?

<p>To group classes and interfaces (A)</p> Signup and view all the answers

Which keyword is used in Java to declare a package?

<p>package (C)</p> Signup and view all the answers

When utilizing the Breadth First Traversal algorithm in graph theory, which data structure is primarily used?

<p>Queue (C)</p> Signup and view all the answers

What will be the output of the provided Java program that adds 'A' and then 'B' at index 0 in an ArrayList?

<p>2 (D)</p> Signup and view all the answers

Can a Java package contain other sub-packages?

<p>Yes, packages can have sub-packages (D)</p> Signup and view all the answers

How do you correctly import a package in Java?

<p>import packageName; (C)</p> Signup and view all the answers

Which of the following is NOT a method for manipulating data in a Java Array?

<p>insert() (C)</p> Signup and view all the answers

What is the outcome when a thread is paused by another thread of the same priority?

<p>It pauses the thread to allow other threads of the same priority to execute. (D)</p> Signup and view all the answers

What type of exception is specifically thrown when the sleep() method is interrupted?

<p>InterruptedException (B)</p> Signup and view all the answers

What functionality does the notifyAll() method provide in terms of thread coordination?

<p>Wakes up all waiting threads on the object's monitor. (D)</p> Signup and view all the answers

Which of the following is the primary method used to create a thread pool in Java?

<p>Executors (B)</p> Signup and view all the answers

What is the most significant advantage of utilizing thread pools in Java applications?

<p>Improved control over thread life cycles and resource allocation. (C)</p> Signup and view all the answers

How can a daemon thread be characterized in Java?

<p>A thread that supports background operations. (D)</p> Signup and view all the answers

Which method would you call to determine if the current thread is designated as a daemon thread?

<p>isDaemon() (A)</p> Signup and view all the answers

In Java, which class embodies the concept of a monitor for synchronization purposes?

<p>Object (A)</p> Signup and view all the answers

In evaluating thread execution, what will happen to a paused thread when notified?

<p>It will either resume or remain paused based on priority. (B)</p> Signup and view all the answers

What happens to a non-daemon thread when all daemon threads are completed?

<p>The non-daemon thread continues to run. (D)</p> Signup and view all the answers

Which method is responsible for creating a new thread from a class that extends the Thread class?

<p>start() (A)</p> Signup and view all the answers

What will occur when the sleep() method is called on a thread?

<p>The thread releases CPU but retains any locks it holds. (A)</p> Signup and view all the answers

Which keyword ensures that a method can only be accessed by one thread at a time?

<p>synchronized (B)</p> Signup and view all the answers

What is the main purpose of the java.sql package in Java?

<p>Engaging in database operations. (B)</p> Signup and view all the answers

What happens if a thread calls the run() method directly rather than using start()?

<p>The current thread will execute the run() method. (A)</p> Signup and view all the answers

Which package is primarily responsible for input and output operations in Java?

<p>java.io (B)</p> Signup and view all the answers

Can multiple packages in Java contain classes with the same name?

<p>Yes, this is allowed. (C)</p> Signup and view all the answers

What is the result of using the deprecated stop() method to stop a thread?

<p>It may leave shared resources in an inconsistent state. (C)</p> Signup and view all the answers

Which of the following describes the term 'fully qualified name' in Java?

<p>Package name followed by class name. (D)</p> Signup and view all the answers

To make one thread wait for another thread's completion, which method is used?

<p>join() (B)</p> Signup and view all the answers

Flashcards

Java package import

Importing classes from external Java packages into a program.

Fully qualified name

Complete name of a class, including the package name.

java.util package

Contains useful utility classes like Scanner and ArrayList.

java.lang package

Automatically imported in all Java programs, built-in classes (String, Math, etc).

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Multithreading in Java

Creating multiple threads to execute code sections simultaneously for faster performance.

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Thread.start()

Used to start or initiate a new thread.

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Thread Priority

Control how threads are prioritized in execution. Default is 5

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Runnable Interface

Java interface that a class must implement to create a thread.

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Thread states

Different possible stages a thread can be in (e.g., running, waiting, blocked).

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Creating threads in Java

Using classes from java.lang.thread

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Clearing a bit to zero

The method clear() in Java sets a bit at a specific index to zero.

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Date before specified date?

The before() method of the Date class checks if a date object is before a given date.

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String key, object value

The Properties class stores objects using strings as keys.

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ArrayList and multiple threads

Accessing a single ArrayList object from multiple threads simultaneously can cause a ConcurrentModificationException.

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ArrayList size after add and insert

Adding elements to an ArrayList using both add() and add(index, element) methods increases the size by 1 per insertion.

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BF Traversal data structure

Breadth-First Traversal of a graph typically uses a Queue data structure.

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Java collections - missing class

The Maps class is not part of the core Java collection framework; Array and Stack are.

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Java Packages: Definition

Java packages are collections of related classes and interfaces.

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Java Package Keyword

The package keyword declares a package in Java.

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Purpose of Java Packages

Java packages are used to organize code, manage names, and control access.

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sleep() method interruption

If a thread is interrupted during a sleep() method call, it throws an InterruptedException.

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notifyAll() method

The notifyAll() method wakes up all threads waiting on the same object's monitor.

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Thread Pool Creation

In Java, you use the Executors class to create pools of threads.

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Thread Pools

Thread pools offer better control and management of thread resources compared to creating threads on demand.

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Daemon Thread

A daemon thread runs in the background to support other tasks and terminates when main thread finishes.

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Checking Daemon Status

Use isDaemon() to check if a thread is a daemon thread.

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Monitor Support

The Object class in Java supports the concept of a monitor, which is used for thread synchronization.

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Thread Permanent Stop

Calling stop() on a thread will permanently stop the program, use interrupt() instead.

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Thread Pause (Sleep)

Pauses a thread temporarily to allow other threads of the same priority to execute.

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Interrupted Exception

Thrown if a thread is interrupted during sleep().

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Study Notes

Java Methods and Classes

  • clear() method: Used to make all bits in a bit set zero.
  • Date class's before() method: Used to check if a Date object is before a specified date.
  • Properties class: Stores values using strings as keys.
  • ArrayList thread safety: Accessing the same ArrayList object by multiple threads results in a ConcurrentModificationException.
  • Adding elements to ArrayList: Adding "B" at index 0 then "A" to an empty ArrayList results in an ArrayList size of 2.
  • Breadth-First Traversal: Uses a Queue data structure.
  • Java Collection Framework Classes: Array, Stack, Queue are part of the collection framework; Maps are not.

Packages in Java

  • Package Definition: package packageName; declares a package.
  • Package Purpose: Packages organize classes and interfaces, prevent naming conflicts, and provide access control.
  • Importing Packages: Use import packageName; or import packageName.*; to import a package or all classes from a package.
  • Fully Qualified Name: The fully qualified name is the package name followed by the class name.
  • Common Packages: java.lang is automatically imported, java.util (contains Scanner and ArrayList), java.io (input/output), java.net (networking), java.sql (database).
  • Subpackages: Packages can contain sub-packages.
  • Java Standard Library: java.util and java.io are part of the Java library. java.graphics is not part.

Multithreading in Java

  • Starting a Thread: Use start(), not run().
  • Thread Priority: Default thread priority is 5.
  • Thread Creation: Implement the Runnable interface or extend the Thread class.
  • Thread States: States include running, waiting, blocked, and ready.
  • Thread Termination: Avoid using stop(), choose other methods to signal termination.
  • Synchronization: synchronized keyword prevents thread interference.
  • Thread Pools: Executors are used to create thread pools for better resource management and thread control.
  • Daemon Threads: Daemon threads run in the background.
  • Thread.sleep(): Pauses the thread temporarily, releasing the CPU while holding any locks.
  • join() Method: Makes one thread wait for another thread to finish.
  • Checking Thread Status: Use isAlive() to check if a thread is currently active.
  • yield() Method: Allows other threads with the same priority to execute.
  • Exceptions: InterruptedException is thrown if an interrupted thread waits for sleep to complete.
  • notifyAll() Method: Wakes up all waiting threads for an object's access.

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