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java classess interview questions

Define class and object. Explain them with an example using java

Class and object – Class: A class is a program construct which encapsulates data and operations on data. In object oriented programming, the class can be viewed as a blue print of an object.

What is a method? Provide several signatures of the methods

What is a method? – A java method is a set of statements to perform a task. A method is placed in a class…

Difference between instance variable and a class variable

Difference between instance variable and a class variable – An instance variable is a variable which has one copy per object / instance. That means every object will have one copy of it…

Explain how to create instance of a class by giving an example

How to create instance of a class – Java supports 3 ways of creating instances…

Define an abstract class. Explain its purpose

Define an abstract class – A class with one of more abstract methods is called an Abstract class…

What is the difference between an Abstract class and Interface?

Abstract class and Interface – An abstract class can have both abstract and concrete methods whereas an interface can have only method signatures…

What is singleton class? Where is it used?

What is singleton class? – A class is defined as singleton class, if and only if it can create only one object…

What is a native method?

What is a native method? – A native method is a method which is implemented in a non-java language that is targeted for a single machine type…

Difference between a public and a non-public class

Difference between a public and a non-public class – A class with access specifier ‘public’ can be accessed across the packages…

What is the purpose of the Runtime class?

Purpose of the Runtime class – The java runtime system can be accessed by the Runtime class…

What is the difference between a static and a non-static inner class?

Static and a non-static inner class – Like static methods and static members are defined in a class, a class can also be static…

Difference between the String and StringBuffer classes

Difference between the String and StringBuffer classes – String class is immutable. The characters of string objects can not be changed / modified…

What is the Dictionary class?

What is the Dictionary class? – The Dictionary class is an abstract class. The class maps keys to values…

What is the ResourceBundle class?

What is the ResourceBundle class? – A ResourceBundle is a group of related sub classes which are sharing the same base name…

What is the Vector class?

What is the Vector class? – The capability of implementing a growable array of object is provided by the class Vector…

What is the SimpleTimeZone class?

What is the SimpleTimeZone class? – SimpleTimeZone is a concrete subclass of TimeZone class…

What is the purpose of the System class?

Purpose of the System class – System class is provided with useful fields (static members) that are pertaining to the environment…

How are this() and super() used with constructors?

How are this() and super() used with constructors? – this() constructor is invoked within a method of a class, if the execution of the constructor is to be done before the functionality of that method…an example using java

Class and object – Class: A class is a program construct which encapsulates data and operations on data. In object oriented programming, the class can be viewed as a blue print of an object.

What is a method? Provide several signatures of the methods

What is a method? – A java method is a set of statements to perform a task. A method is placed in a class…

Difference between instance variable and a class variable

Difference between instance variable and a class variable – An instance variable is a variable which has one copy per object / instance. That means every object will have one copy of it…

Explain how to create instance of a class by giving an example

How to create instance of a class – Java supports 3 ways of creating instances…

Define an abstract class. Explain its purpose

Define an abstract class – A class with one of more abstract methods is called an Abstract class…

What is the difference between an Abstract class and Interface?

Abstract class and Interface – An abstract class can have both abstract and concrete methods whereas an interface can have only method signatures…

What is singleton class? Where is it used?

What is singleton class? – A class is defined as singleton class, if and only if it can create only one object…

What is a native method?

What is a native method? – A native method is a method which is implemented in a non-java language that is targeted for a single machine type…

Difference between a public and a non-public class

Difference between a public and a non-public class – A class with access specifier ‘public’ can be accessed across the packages…

What is the purpose of the Runtime class?

Purpose of the Runtime class – The java runtime system can be accessed by the Runtime class…

What is the difference between a static and a non-static inner class?

Static and a non-static inner class – Like static methods and static members are defined in a class, a class can also be static…

Difference between the String and StringBuffer classes

Difference between the String and StringBuffer classes – String class is immutable. The characters of string objects can not be changed / modified…

What is the Dictionary class?

What is the Dictionary class? – The Dictionary class is an abstract class. The class maps keys to values…

What is the ResourceBundle class?

What is the ResourceBundle class? – A ResourceBundle is a group of related sub classes which are sharing the same base name…

What is the Vector class?

What is the Vector class? – The capability of implementing a growable array of object is provided by the class Vector…

What is the SimpleTimeZone class?

What is the SimpleTimeZone class? – SimpleTimeZone is a concrete subclass of TimeZone class…

What is the purpose of the System class?

Purpose of the System class – System class is provided with useful fields (static members) that are pertaining to the environment…

How are this() and super() used with constructors?

How are this() and super() used with constructors? – this() constructor is invoked within a method of a class, if the execution of the constructor is to be done before the functionality of that method…

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