Hello,
Dear Students, in this blog from Java Training In Pune, I am discussing the most commonly occurring interview questions on Core java. While preparing for interviews one of the most important for student is technical preparation. Sometimes you will get direct questions and sometimes twisted questions so today I will discuss them.
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What is platform?
Platform is a environment where software is running. Java provides software based platform.
Platform can be hardware based, software based.
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What is byte Code?
Compiled java Code is known as byte Code. Byte Code is also called magic Code also. It will provide security to java Code.
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What are the types of data Types in java?
There are two types of data types Primitives and non primitives
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What are static variables?
The variables which are declared using static keyword is known as static variables.
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What is JDK?
JDK is java Development Kit. It is software for creating and running java programs. Currently jdk16 is running.
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Why java is Called Write Once Run anywhere?
Because of Byte Code java is Called write Once Run Anywhere. Because Compiler converts into Byte Code (.Class File).
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What is Class Loader?
Class Loader is used to Load the Class. It is a sub System of JVM. When we run a java programs the first thing is class Loader. Three built-in class Loaders in JVM.
Bootstrap Class Loader, Extension Class Loader, System/Application Class Loader.
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Can Local Variables have Default Values?
No. Compiler does not have any default value.
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What are Types of Variables in java?
In java, based on Scope of variable. Variables are 3 types
Local Variable, Instance Variable, Static Variable
Local Variables: The Variables which are declared inside a method are called Local Variables.
The Scope of Local Variables inside a method only.
Instance Variables: The variables which are declared in a class are called instance variables. The Scope of instance Variables are you can access any where inside a class. Compiler will replace default value for instance Variables .
Static Variable: The variables which are sharable will all objects are called Static Variables. Static Variables are declared using static keyword.
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What are Static Methods?
Methods which are declared using static Keyword are static methods. You can Access only static variables inside a static methods. All static methods are accessed directly.
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Can we overload main method in java?
Yes we can overload main method . the compilation start from main only. Because JVM understands public static void main (String [] args) only. Main method is entry point for program.
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What is method overloading?
In java method overloading is Same method name in a class with different types of parameters. Method overloading provides manage ability and read ability. You can use same method name in a class with different types of parameters. For example System.out.println () is overloaded method.
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Why does pointers are not used in java?
Pointers are not safe(unsafe).Pointers are complicated for beginners . Java focuses on Code Simplicity. So java does not use pointers.
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What is JIT?
JIT is Just in Time . It is translator of source Code to machine executable code.JIT is Part of JVM.It will improvers the code performances.
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How you will declare infinite Loop in java.
In java you can make any loop as infinite loop
Using for loop
- For(;;){ // your Logic}
Using while Loop
While(true)
{
//your Logic
}
Do
{
}while(true);
You can use any one of Loop for infinite Loop.
In java there are four(4) loops. While loop, for loop, do while loop, enhanced for loop.It is also called for each loop.
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What are difference between for loop and enhanced for loop(for each loop)
For each loop is mainly used to access the objects and Arrays. It is very simplified one. Where you can declare variable, no need for condition and increment / decrement variables. It is used to iterate only arrays and objects only. In for Loop we need to declare variable, writes condition, and write increment, decrement based on logic
Syntax of both Loops
For Loop Syntax
For(variable_declare; condition; increment/decrement)
{
// Logic
}
Enhanced for loop
For(variable : array/object)
{
// Logic
}
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Write difference between equals() and (==) in java?
Equals () is a method in Object class where (==) is binary operator
Equals () method will check the equality of content of objects. Where double equals (==) will check the address of the objects.
Simple way equals method for content checking. And double equals for address checking.
What is constructors in java?
Constructor is a special method that get executed when we create a objects of a class. It is used to initialized the instance variables.
What are the Types of constructors in java?
There are two types of constructors in java.1) Default constructor2)Parameterized constructor.
How to create a anonymous object in java?
Using new keyword we can create a anonymous object. For example I am creating Student class then in main we can create a anonymous object by writing new Student ();.
what is super keyword?
In order to access the method and instance variable from parent class . Java provides super keyword. We can use Super() method to access parent class constructor .Super() method should be written the first line of a code.
what constructor overloading?
Just like method overloading even we can overload constructor . In a class same class name with different , different types of parameters is called constructor overloading. Java Course In Pune can teach same constructor name with different types of parameters.
What are access specifiers in java?
Access Specifiers are access ability of a member variable or methods where developers can decide which part of a code can be accessed by end user. The default access specifiers is default in java. Java provides public, private , protected and default access specifier
How to create Arrays of Objects in java?
We can create arrays of objects in java. Because in java array is objects. For example
I am creating Student class in main we can create Arrays of objects like
Student stobj[] = new Student[3];
After creating arrays of object we can initialize like this
stobj[0]=new Student();
stobj[1]=new Student();
stobj[2]=new Student();
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What are Packages in java?
Package is Collection of classes, interfaces,and subpackage. Package will provides the encapsulation where all classes are Placed in one folder. Package provides manage ability. Multiple Packages can have same class name. Package Provides access protection. In java there are two types of packages Built in package , user defined Package. Package is used for easy maintenance
How to run a package using command prompt?
Package can be run using command prompt also . we can write javac –d packagename, (this is for compilation). To run a package we use java packagename.classname.
How to access the package?
To access package we need to import a package .For importing we need to write import package.*; Here package is name of the package.
What is this keyword in java?
This is a keyword in java. In a class if you have ambiguity between member variable and parameter of a constructor or a method you can use this keyword. This keyword always refers to current class member variables (instance variables).
How to invoke a parameterized constructor from default constructor?
Using this () method we can call a one constructor from another constructor. If you want to achieve constructor chaining or reuse of constructor we can use this ().One
What are wrapper classes?
In Object Oriented Programming Language everything is an object .So in collection topic it requires Wrapper classes convert primitives to objects and primitives to object So for conversion Wrapper classes are used in java.
What are the Uses of Wrapper classes?
The Uses of Wrapper classess are
- Wrapper classes helps in serialization. We can convert primitives to Objects using wrapper class.
- Mainly in Collection Framework we are working with objects. Like Array List, Linked List,etc are working with wrapper class only.
In java there are 8 Wrapper classes. Which converts object to primitives .
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What is Auto Boxing?
The automatic conversion of primitives data type to objects is known as Auto Boxing which happens automatically.
For example
In a class we can write like
Int x=100;
Integer i=Integer.ValueOf(x);
Here x is converted as Integer object i. Which will happen automatically is called auto boxing.
What is final keyword in java?
In order to declare constant in java. We can use a final keyword. Final keyword makes variable as a constant. We can ‘t change its value. We can declare variable as a final variable as a static variable. One rule for final keyword is we need to initialize it. Un initialized final variable is known as blank final variable. If we make any variable as final its value does not changes. We cannot override final method which will stop inheritance. Ask to the industry experts of Java Classes In Pune for more information by calling them.
Author:-
Sangam Bhagyashri
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