0
Q:

Which of the following statements are equal for a variable declared in the interface ?

1. int X=10
2. public int X=10
3. public static final int X=10

A) Only 1 and 2 are equal B) Only 2 and 3 are equal
C) All are unequal D) All are equal

Answer:   D) All are equal



Explanation:

All the statements are equal because inside an interface a variable declared will be public static final by default 

Subject: Java
Job Role: IT Trainer
Q:

What is the common usage of serialization? What exceptions occur during serialization?

Answer

The object need to be serialized when it’s sent over a network and when it’s state is saved. Exceptions which occur during serialization are:


a. transient fields


b. when the base class is serialized then only base class fields are handled.


c. static fields are ignored because they are not part of any state.

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Subject: Java

1 2360
Q:

What is Shallow and deep cloning in Java?

Answer

Cloning refers to creating duplicate copies of objects in java.


Shallow Cloning: Shallow cloning is a bitwise copy of an object. New object is created which is an exact copy that of the original one. In case any objects are referring the fields of these objects, just the references are copied.


Deep Cloning: In deep cloning, complete duplicate copy of the original copy is created. Deep cloning creates not only the primitive values of the original objects but also copies all its sub objects as well.


Clonable interface is used to perform cloning in java.

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Subject: Java

0 1670
Q:

Why do we need wrapper classes in Java?

Answer

Dealing with primitives as objects is easier at times. Most of the objects collection store objects and not primitive types. Many utility methods are provided by wrapper classes. To get these advantages we need to use wrapper classes. As they are objects, they can be stored in any of the collection and pass this collection as parameters to the methods.


 


Features of the Java wrapper Classes:


- Wrapper classes convert numeric strings into numeric values.


- The way to store primitive data in an object.


- The valueOf() method is available in all wrapper classes except Character


- All wrapper classes have typeValue() method. This method returns the value of the object as its primitive type.

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Subject: Java

0 2745
Q:

How does thread synchronization occurs inside a monitor?

Answer

A Monitor defines a lock and condition variables for managing concurrent access to shared data. The monitor uses the lock to ensure that only a single thread inactive in the monitor code at any time.


A monitor allows only one thread to lock an object at once.

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Subject: Java

0 2418
Q:

What is Auto boxing and unboxing?

Answer

Autoboxing is the process of converting a primitive type data into its corresponding wrapper class object instance.


Example:


Integer number = new Integer (100); // number is now refers to the object 100


 


Unboxing is the process of converting a wrapper instance into a primitive type.


Example: 


Integer number = new Integer (100); 


int num = number;// without type casting number would be changed into int type

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Subject: Java

0 1504
Q:

What are Native methods in Java?

Answer

Java applications can call code written in C, C++, or assembler. This is sometimes done for performance and sometimes to access the underlying host operating system or GUI API using the JNI.


 


The steps for doing that are:


First write the Java code and compile it


Then create a C header file


Create C stubs file


Write the C code


Create shared code library (or DLL)


Run application

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Subject: Java

0 1668
Q:

What is the SimpleTimeZone class?

Answer

SimpleTimeZone is a concrete subclass of TimeZone class. The TimeZone class represents a time zone, that is to be used with Gregorian calendar.


The SimpleTimeZone is created by using the base time zone offset from GMT time zone ID and rules, for starting and ending the time of daylight.

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Subject: Java

0 1679
Q:

What is the Dictionary class?

Answer

- The Dictionary class is an abstract class.


- Classes like Hashtable which map keys to values inherit from this class. 


- An object can be looked for if a dictionary and a key is provided.


- Any non-null object can be used as a key and as a value.

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Subject: Java

1 1502