#Java_Interview_Question

115)What is the difference between notify() and notifyAll()?

The notify() is used to unblock one waiting thread whereas notifyAll() method is used to unblock all the threads in waiting state.

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116)What is deadlock?

Deadlock is a situation when two threads are waiting on each other to release a resource. Each thread waiting for a resource which is held by the other waiting thread.

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👉Motivation

Consider the domain of "thread scheduling".

There are two types of thread schedulers, and two types of operating systems or "platforms". Given this approach to specialization, we have to define a class for each permutation of these two dimensions. If we add a new platform (say ... Java's Virtual Machine), what would our hierarchy look like?

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What if we had three kinds of thread schedulers, and four kinds of platforms? What if we had five kinds of thread schedulers, and ten kinds of platforms? The number of classes we would have to define is the product of the number of scheduling schemes and the number of platforms.

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The Bridge design pattern proposes refactoring this exponentially explosive inheritance hierarchy into two orthogonal hierarchies – one for platform-independent abstractions, and the other for platform-dependent implementations.

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117) What is Garbage Collection?

Garbage collection is a process of reclaiming the runtime unused objects.It is performed for memory management.

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👉Java Garbage Collection

▪️In java, garbage means unreferenced objects.

▪️Garbage Collection is process of reclaiming the runtime unused memory automatically. In other words, it is a way to destroy the unused objects.

▪️To do so, we were using free() function in C language and delete() in C++. But, in java it is performed automatically. So, java provides better memory management.

👉Advantage of Garbage Collection

1️⃣It makes java memory efficient because garbage collector removes the unreferenced objects from heap memory.

2️⃣It is automatically done by the garbage collector(a part of JVM) so we don't need to make extra efforts.

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#Bridge_Design_Pattern

👉Discussion

Decompose the component's interface and implementation into orthogonal class hierarchies. The interface class contains a pointer to the abstract implementation class. This pointer is initialized with an instance of a concrete implementation class, but all subsequent interaction from the interface class to the implementation class is limited to the abstraction maintained in the implementation base class. The client interacts with the interface class, and it in turn "delegates" all requests to the implementation class.

The interface object is the "handle" known and used by the client; while the implementation object, or "body", is safely encapsulated to ensure that it may continue to evolve, or be entirely replaced (or shared at run-time.

👉Use the Bridge pattern when:

1️⃣you want run-time binding of the implementation,
2️⃣you have a proliferation of classes resulting from a coupled interface and numerous implementations,
3️⃣you want to share an implementation among multiple objects,
4️⃣you need to map orthogonal class hierarchies.

👉Consequences include:

1️⃣decoupling the object's interface,
2️⃣improved extensibility (you can extend (i.e. subclass) the abstraction and implementation hierarchies independently),
3️⃣hiding details from clients.

👉Bridge is a synonym for the "handle/body" idiom. This is a design mechanism that encapsulates an implementation class inside of an interface class. The former is the body, and the latter is the handle. The handle is viewed by the user as the actual class, but the work is done in the body. "The handle/body class idiom may be used to decompose a complex abstraction into smaller, more manageable classes. The idiom may reflect the sharing of a single resource by multiple classes that control access to it (e.g. reference counting)."

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👉Structure

The Client doesn't want to deal with platform-dependent details. The Bridge pattern encapsulates this complexity behind an abstraction "wrapper".

Bridge emphasizes identifying and decoupling "interface" abstraction from "implementation" abstraction.

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#Java_Interview_Question

118) What is gc()?

gc() is a daemon thread.gc() method is defined in System class that is used to send request to JVM to perform garbage collection.

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119) What is the purpose of finalize() method?

finalize() method is invoked just before the object is garbage collected.It is used to perform cleanup processing.

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120) Can an unrefrenced objects be refrenced again?

Yes.

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121)What kind of thread is the Garbage collector thread?

Daemon thread.

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👉Example

The Bridge pattern decouples an abstraction from its implementation, so that the two can vary independently. A household switch controlling lights, ceiling fans, etc. is an example of the Bridge. The purpose of the switch is to turn a device on or off. The actual switch can be implemented as a pull chain, simple two position switch, or a variety of dimmer switches.

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#Java_Interview_Question

122)What is difference between final, finally and finalize?

final: final is a keyword, final can be variable, method or class.You, can't change the value of final variable, can't override final method, can't inherit final class.
finally: finally block is used in exception handling. finally block is always executed.
finalize():finalize() method is used in garbage collection.finalize() method is invoked just before the object is garbage collected.The finalize() method can be used to perform any cleanup processing.

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