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JAVA Programming
How does the hashCode() method work in java.lang.Object class?
The hashCode() method in the java.lang.Object class returns a hash code value for the object on which it is invoked. This method returns an integer value that represents the object’s memory address in the JVM’s heap memory.
The hashCode() method is used in conjunction with the equals() method to determine if two objects are equal. If two objects are equal according to the equals() method, their hash codes must also be equal. However, two objects with the same hash code may not necessarily be equal according to the equals() method.
It is important to note that the hashCode() method is not guaranteed to return a unique value for each object. Two different objects may have the same hash code, but this is called a hash collision. The hashCode() method is designed to provide a good distribution of hash codes for objects so that they can be efficiently stored in data structures like hash tables.
What is the use of java.lang.Thread class in Java programming?
In Java programming, the java.lang.Thread class is used for creating and managing threads. A thread is a lightweight process that can execute concurrently with other threads in a program, allowing for multi-tasking and improved performance.
The Thread class provides several methods for creating and controlling threads, such as:
start(): creates a new thread and starts its execution.sleep(): pauses the execution of the current thread for a specified amount of time.join(): waits for a thread to finish its execution before continuing the execution of the current thread.interrupt(): interrupts the execution of a thread, causing it to terminate.
Additionally, the Thread class provides mechanisms for synchronizing access to shared resources and communication between threads, such as:
wait(),notify(), andnotifyAll(): methods for inter-thread communication and synchronization.synchronized: keyword for creating synchronized blocks of code to ensure mutual exclusion and thread safety.
The Thread class is a fundamental part of Java’s multi-threading capabilities, enabling developers to create complex, concurrent programs that can take advantage of modern computer architectures.
Can you explain the difference between Thread and Runnable in java.lang package?
In Java, Thread and Runnable are related but distinct concepts. A Thread represents an individual path of execution within a program, while a Runnable represents a task that can be executed by a thread.
To create a new thread in Java, you can either extend the Thread class or implement the Runnable interface. When extending Thread, you override the run() method to define the behavior of the thread. When implementing Runnable, you define the behavior of the thread in the run() method of a separate class that implements Runnable. You then pass an instance of that class to the constructor of a new Thread object, and call the start() method on that object to begin execution of the new thread.
Here’s an example of extending the Thread class:
class MyThread extends Thread {
public void run() {
System.out.println("Hello from MyThread!");
}
}
MyThread t = new MyThread();
t.start();
And here’s an example of implementing the Runnable interface:
class MyRunnable implements Runnable {
public void run() {
System.out.println("Hello from MyRunnable!");
}
}
MyRunnable r = new MyRunnable();
Thread t = new Thread(r);
t.start();
Both of these examples create a new thread that prints a message to the console. The first example does so by overriding the run() method of the Thread class itself, while the second example does so by implementing the run() method of a separate class that is passed to the constructor of a new Thread object.
What is the use of java.lang.Runnable interface in Java programming?
The java.lang.Runnable interface in Java programming is used to define a task that can be executed in a separate thread. It has a single method called run() that takes no arguments and returns no value. This method represents the task that will be executed when the thread is started.
The Runnable interface is often used as an alternative to extending the Thread class for creating a new thread. Instead of creating a new thread by extending the Thread class, we can create a new thread by implementing the Runnable interface and passing an instance of the class to the Thread constructor.
Here is an example of implementing the Runnable interface:
class MyRunnable implements Runnable {
public void run() {
// code to be executed in a separate thread
}
}
And here is an example of creating a new thread using the MyRunnable class:
Thread thread = new Thread(new MyRunnable());
thread.start();
This creates a new thread and starts executing the run() method in the MyRunnable class. By implementing the Runnable interface, we can separate the task from the thread implementation and reuse the task in multiple threads.
Can you explain the difference between sleep() and wait() methods in java.lang.Thread class?
There are several differences between the sleep() and wait() methods in the java.lang.Thread class:
Purpose: The
sleep()method is used to pause the execution of the current thread for a specified period of time, while thewait()method is used to pause the execution of a thread until a certain condition is met.Lock: The
sleep()method does not release the lock on the object, while thewait()method releases the lock on the object and waits to be notified.Notification: The
sleep()method does not require any notification to resume execution, while thewait()method requires a notification to resume execution. This notification can be done by another thread calling thenotify()ornotifyAll()method on the same object.Exception: The
sleep()method throws an InterruptedException if the thread is interrupted, while thewait()method throws an InterruptedException if the thread is interrupted, or an IllegalMonitorStateException if it is called without holding the lock on the object.
In summary, sleep() is used to pause the execution of a thread for a specified period of time, while wait() is used to pause the execution of a thread until a certain condition is met and requires a notification to resume execution.
What is the purpose of java.lang.Class class in Java programming?
The java.lang.Class class in Java is used to represent the classes and interfaces of Java programs at runtime. It is used to access the metadata of the class such as its name, modifiers, superclass, interfaces, methods, fields, annotations, etc.
Class objects are created automatically by the Java Virtual Machine (JVM) when a class is loaded into memory, and can be obtained in Java code using the .class operator, or by calling the getClass() method on an object.
The Class class also provides methods to create new instances of the class, check if a class is an interface or primitive type, check if two classes are the same, and to get the class loader that loaded the class.
Overall, the Class class is an important part of Java’s reflection API, which allows Java programs to introspect and manipulate Java classes and objects at runtime.
Can you explain the use of java.lang.ClassLoader class in Java programming?
In Java, the ClassLoader class is responsible for dynamically loading Java classes at runtime. It loads the classes from different sources such as a local file system, network, or an archive file, and provides an instance of the class for use by the application.
The ClassLoader class is part of the java.lang package and is an abstract class that provides a framework for loading classes. The ClassLoader has three primary responsibilities:
Finding and loading classes: The
ClassLoaderlooks for the class file on the file system or other sources and loads the class into the memory.Linking the class: Once the class is loaded, the
ClassLoaderlinks the class by verifying and preparing the class for execution.Defining the class: The
ClassLoadercreates aClassobject for the loaded class, which can be used to create new instances of the class.
Java has three built-in implementations of ClassLoader:
Bootstrap ClassLoader: It is responsible for loading the core Java classes such as
java.lang.Object,java.lang.String, etc. It is written in native code and is part of the Java virtual machine (JVM).Extension ClassLoader: It is responsible for loading the classes from the extension directories such as JAR files from the
lib/extdirectory.System ClassLoader: It is responsible for loading the classes from the system classpath, which includes user-defined classpath directories and JAR files.
Developers can also create their own custom ClassLoader by extending the ClassLoader class and implementing the findClass() method to load classes from custom sources such as a database, remote server, or encrypted files.
Questions on Chapter 17