Java Interview Question 4
Q: What is the difference between declaring a variable and defining a variable?
A: In declaration we just mention the type of the variable and it's name. We do not initialize it. But defining means declaration + initialization.
e.g String s; is just a declaration while String s = new String ("abcd"); Or String s = "abcd"; are both definitions.
Q:What is the default value of an object reference declared as an instance variable?
A: null unless we define it explicitly.
Q: Can a top level class be private or protected?
A: No. A top level class can not be private or protected. It can have either "public" or no modifier. If it does not have a modifier it is supposed to have a default access.If a top level class is declared as private the compiler will complain that the "modifier private is not allowed here". This means that a top level class can not be private. Same is the case with protected.
Q: What type of parameter passing does Java support?
A: In Java the arguments are always passed by value .
Q: Primitive data types are passed by reference or pass by value?
A: Primitive data types are passed by value.
Q:Objects are passed by value or by reference?
A: Java only supports pass by value. With objects, the object reference itself is passed by value and so both the original reference and parameter copy both refer to the same object .
Q: What is serialization?
A: Serialization is a mechanism by which you can save the state of an object by converting it to a byte stream.
Q: How do I serialize an object to a file?
A: The class whose instances are to be serialized should implement an interface Serializable. Then you pass the instance to the ObjectOutputStream which is connected to a fileoutputstream. This will save the object to a file.
Q: Which methods of Serializable interface should I implement?
A: The serializable interface is an empty interface, it does not contain any methods. So we do not implement any methods.
Q: How can I customize the seralization process? i.e. how can one have a control over the serialization process?
A: Yes it is possible to have control over serialization process. The class should implement Externalizable interface. This interface contains two methods namely readExternal and writeExternal. You should implement these methods and write the logic for customizing the serialization process.
Q: What is the common usage of serialization?
A: Whenever an object is to be sent over the network, objects need to be serialized. Moreover if the state of an object is to be saved, objects need to be serilazed.
Q: What is Externalizable interface?
A: Externalizable is an interface which contains two methods readExternal and writeExternal. These methods give you a control over the serialization mechanism. Thus if your class implements this interface, you can customize the serialization process by implementing these methods.
Q: When you serialize an object, what happens to the object references included in the object?
A: The serialization mechanism generates an object graph for serialization. Thus it determines whether the included object references are serializable or not. This is a recursive process. Thus when an object is serialized, all the included objects are also serialized alongwith the original obect.
Q: What one should take care of while serializing the object?
A: One should make sure that all the included objects are also serializable. If any of the objects is not serializable then it throws a NotSerializableException.
Q: What happens to the static fields of a class during serialization?
A:
There are three exceptions in which serialization doesnot necessarily read and write to the stream. These are
1. Serialization ignores static fields, because they are not part of ay particular state state.
2. Base class fields are only hendled if the base class itself is serializable.
3. Transient fields.
Q: How are Observer and Observable used?
A: Objects that subclass the Observable class maintain a list of observers. When an Observable object is updated it invokes the update() method of each of its observers to notify the observers that it has changed state. The Observer interface is implemented by objects that observe Observable objects.
Q: What is synchronization and why is it important?
A: With respect to multithreading, synchronization is the capability to control
the access of multiple threads to shared resources. Without synchronization, it is possible for one thread to modify a shared object while another thread is in the process of using or updating that object's value. This often leads to significant errors.
Q: How does Java handle integer overflows and underflows?
A: It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.
Q: Does garbage collection guarantee that a program will not run out of memory?
A: Garbage collection does not guarantee that a program will not run out of memory. It is possible for programs to use up memory resources faster than they are garbage collected. It is also possible for programs to create objects that are not subject to garbage collection
.
Q: What is the difference between preemptive scheduling and time slicing?
A: Under preemptive scheduling, the highest priority task executes until it enters the waiting or dead states or a higher priority task comes into existence. Under time slicing, a task executes for a predefined slice of time and then reenters the pool of ready tasks. The scheduler then determines which task should execute next, based on priority and other factors.
A: In declaration we just mention the type of the variable and it's name. We do not initialize it. But defining means declaration + initialization.
e.g String s; is just a declaration while String s = new String ("abcd"); Or String s = "abcd"; are both definitions.
Q:What is the default value of an object reference declared as an instance variable?
A: null unless we define it explicitly.
Q: Can a top level class be private or protected?
A: No. A top level class can not be private or protected. It can have either "public" or no modifier. If it does not have a modifier it is supposed to have a default access.If a top level class is declared as private the compiler will complain that the "modifier private is not allowed here". This means that a top level class can not be private. Same is the case with protected.
Q: What type of parameter passing does Java support?
A: In Java the arguments are always passed by value .
Q: Primitive data types are passed by reference or pass by value?
A: Primitive data types are passed by value.
Q:Objects are passed by value or by reference?
A: Java only supports pass by value. With objects, the object reference itself is passed by value and so both the original reference and parameter copy both refer to the same object .
Q: What is serialization?
A: Serialization is a mechanism by which you can save the state of an object by converting it to a byte stream.
Q: How do I serialize an object to a file?
A: The class whose instances are to be serialized should implement an interface Serializable. Then you pass the instance to the ObjectOutputStream which is connected to a fileoutputstream. This will save the object to a file.
Q: Which methods of Serializable interface should I implement?
A: The serializable interface is an empty interface, it does not contain any methods. So we do not implement any methods.
Q: How can I customize the seralization process? i.e. how can one have a control over the serialization process?
A: Yes it is possible to have control over serialization process. The class should implement Externalizable interface. This interface contains two methods namely readExternal and writeExternal. You should implement these methods and write the logic for customizing the serialization process.
Q: What is the common usage of serialization?
A: Whenever an object is to be sent over the network, objects need to be serialized. Moreover if the state of an object is to be saved, objects need to be serilazed.
Q: What is Externalizable interface?
A: Externalizable is an interface which contains two methods readExternal and writeExternal. These methods give you a control over the serialization mechanism. Thus if your class implements this interface, you can customize the serialization process by implementing these methods.
Q: When you serialize an object, what happens to the object references included in the object?
A: The serialization mechanism generates an object graph for serialization. Thus it determines whether the included object references are serializable or not. This is a recursive process. Thus when an object is serialized, all the included objects are also serialized alongwith the original obect.
Q: What one should take care of while serializing the object?
A: One should make sure that all the included objects are also serializable. If any of the objects is not serializable then it throws a NotSerializableException.
Q: What happens to the static fields of a class during serialization?
A:
There are three exceptions in which serialization doesnot necessarily read and write to the stream. These are
1. Serialization ignores static fields, because they are not part of ay particular state state.
2. Base class fields are only hendled if the base class itself is serializable.
3. Transient fields.
Q: How are Observer and Observable used?
A: Objects that subclass the Observable class maintain a list of observers. When an Observable object is updated it invokes the update() method of each of its observers to notify the observers that it has changed state. The Observer interface is implemented by objects that observe Observable objects.
Q: What is synchronization and why is it important?
A: With respect to multithreading, synchronization is the capability to control
the access of multiple threads to shared resources. Without synchronization, it is possible for one thread to modify a shared object while another thread is in the process of using or updating that object's value. This often leads to significant errors.
Q: How does Java handle integer overflows and underflows?
A: It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.
Q: Does garbage collection guarantee that a program will not run out of memory?
A: Garbage collection does not guarantee that a program will not run out of memory. It is possible for programs to use up memory resources faster than they are garbage collected. It is also possible for programs to create objects that are not subject to garbage collection
.
Q: What is the difference between preemptive scheduling and time slicing?
A: Under preemptive scheduling, the highest priority task executes until it enters the waiting or dead states or a higher priority task comes into existence. Under time slicing, a task executes for a predefined slice of time and then reenters the pool of ready tasks. The scheduler then determines which task should execute next, based on priority and other factors.
Question: When a thread is created and started, what is its initial state?
Answer: A thread is in the ready state after it has been created and started.
Question: Can an anonymous class be declared as implementing an interface and extending a class?
Answer: An anonymous class may implement an interface or extend a superclass, but may not be declared to do both.
Question: What is the range of the short type?
Answer: The range of the short type is -(2^15) to 2^15 - 1.
Question: What is the range of the char type?
Answer: The range of the char type is 0 to 2^16 - 1.
Question: In which package are most of the AWT events that support the event-delegation model defined?
Answer: Most of the AWT-related events of the event-delegation model are defined in the java.awt.event package. The AWTEvent class is defined in the java.awt package.
Question: What is the immediate superclass of Menu?
Answer: MenuItem
Question: What is the purpose of finalization?
Answer: The purpose of finalization is to give an unreachable object the opportunity to perform any cleanup processing before the object is garbage collected.
Question: Which class is the immediate superclass of the MenuComponent class.
Answer: Object
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