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JAVA BASIC STRUCTURE NOTES, Exams of Java Programming

Kurukshetra University Java Programming

QUESTION BANK 2MARKS ONLY FOR FINAL EXAMS

Typology: Exams

2019/2020

Uploaded on 04/27/2020

suman-kashyap-1 🇮🇳

5 documents

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1) What is Java?

Java is the high-level, object-oriented, robust, secure programming language, platform-

independent, high performance, Multithreaded, and portable programming language. It was

developed by James Gosling in June 1991. It can also be known as the platform as it

provides its own JRE and API.

2) What are the differences between C++ and Java?

The differences between C++ and Java are given in the following table.

Comparison

Index

C++ Java

Platform-

independent

C++ is platform-dependent. Java is platform-independent.

Mainly used for C++ is mainly used for

system programming.

Java is mainly used for application

programming. It is widely used in

window, web-based, enterprise and

mobile applications.

Design Goal C++ was designed for

systems and applications

programming. It was an

extension of C programming

language.

Java was designed and created as

an interpreter for printing systems

but later extended as a support

network computing. It was

designed with a goal of being easy

to use and accessible to a broader

audience.

Goto C++ supports

the goto statement.

Java doesn't support the goto

statement.

Multiple

inheritance

C++ supports multiple

inheritance.

Java doesn't support multiple

inheritance through class. It can be

achieved by interfaces in java.

Operator

Overloading

C++ supports operator

overloading.

Java doesn't support operator

overloading.

Pointers C++ supports pointers. You

can write pointer program in

C++.

Java supports pointer internally.

However, you can't write the

pointer program in java. It means

java has restricted pointer support

in java.

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What is Java? Java is the high-level, object-oriented, robust, secure programming language, platform- independent, high performance, Multithreaded, and portable programming language. It was developed by James Gosling in June 1991. It can also be known as the platform as it provides its own JRE and API.
What are the differences between C++ and Java? The differences between C++ and Java are given in the following table. Comparison Index C++ Java Platform- independent C++ is platform-dependent. Java is platform-independent. Mainly used for C++ is mainly used for system programming. Java is mainly used for application programming. It is widely used in window, web-based, enterprise and mobile applications. Design Goal C++ was designed for systems and applications programming. It was an extension of C programming language. Java was designed and created as an interpreter for printing systems but later extended as a support network computing. It was designed with a goal of being easy to use and accessible to a broader audience. Goto C++ supports the goto statement. Java doesn't support the goto statement. Multiple inheritance C++ supports multiple inheritance. Java doesn't support multiple inheritance through class. It can be achieved by interfaces in java. Operator Overloading C++ supports operator overloading. Java doesn't support operator overloading. Pointers C++ supports^ pointers. You can write pointer program in C++. Java supports pointer internally. However, you can't write the pointer program in java. It means java has restricted pointer support in java.

Compiler and Interpreter C++ uses compiler only. C++ is compiled and run using the compiler which converts source code into machine code so, C++ is platform dependent. Java uses compiler and interpreter both. Java source code is converted into bytecode at compilation time. The interpreter executes this bytecode at runtime and produces output. Java is interpreted that is why it is platform independent. Call by Value and Call by reference C++ supports both call by value and call by reference. Java supports call by value only. There is no call by reference in java. Structure and Union C++ supports structures and unions. Java doesn't support structures and unions. Thread Support C++ doesn't have built-in support for threads. It relies on third-party libraries for thread support. Java has built-in thread support. Documentation comment C++ doesn't support documentation comment. Java supports documentation comment (/** ... */) to create documentation for java source code. Virtual Keyword C++ supports virtual keyword so that we can decide whether or not override a function. Java has no virtual keyword. We can override all non-static methods by default. In other words, non- static methods are virtual by default. unsigned right shift >>> C++ doesn't support >>> operator. Java supports unsigned right shift

operator that fills zero at the top for the negative numbers. For positive numbers, it works same like >> operator. Inheritance Tree C++ creates a new inheritance tree always. Java uses a single inheritance tree always because all classes are the child of Object class in java. The object class is the root of the inheritance tree in java. Hardware C++ is nearer to hardware. Java is not so interactive with hardware. Object-oriented C++ is an object-oriented language. However, in C Java is also an object- oriented language. However,

o High Performance: Java is faster than other traditional interpreted programming languages because Java bytecode is "close" to native code. It is still a little bit slower than a compiled language (e.g., C++). o Multithreaded: We can write Java programs that deal with many tasks at once by defining multiple threads. The main advantage of multi-threading is that it doesn't occupy memory for each thread. It shares a common memory area. Threads are important for multi-media, Web applications, etc. o Distributed: Java is distributed because it facilitates users to create distributed applications in Java. RMI and EJB are used for creating distributed applications. This feature of Java makes us able to access files by calling the methods from any machine on the internet. o Dynamic: Java is a dynamic language. It supports dynamic loading of classes. It means classes are loaded on demand. It also supports functions from its native languages, i.e., C and C++.

What do you understand by Java virtual machine? Java Virtual Machine is a virtual machine that enables the computer to run the Java program. JVM acts like a run-time engine which calls the main method present in the Java code. JVM is the specification which must be implemented in the computer system. The Java code is compiled by JVM to be a Bytecode which is machine independent and close to the native code.
What is the difference between JDK, JRE, and JVM? JVM JVM is an acronym for Java Virtual Machine; it is an abstract machine which provides the runtime environment in which Java bytecode can be executed. It is a specification which specifies the working of Java Virtual Machine. Its implementation has been provided by Oracle and other companies. Its implementation is known as JRE. JVMs are available for many hardware and software platforms (so JVM is platform dependent). It is a runtime instance which is created when we run the Java class. There are three notions of the JVM: specification, implementation, and instance.

JRE

JRE stands for Java Runtime Environment. It is the implementation of JVM. The Java Runtime Environment is a set of software tools which are used for developing Java applications. It is used to provide the runtime environment. It is the implementation of JVM. It physically exists. It contains a set of libraries + other files that JVM uses at runtime. JDK JDK is an acronym for Java Development Kit. It is a software development environment which is used to develop Java applications and applets. It physically exists. It contains JRE + development tools. JDK is an implementation of any one of the below given Java Platforms released by Oracle Corporation: o Standard Edition Java Platform o Enterprise Edition Java Platform o Micro Edition Java Platform More Details.

How many types of memory areas are allocated by JVM? Many types:

Class(Method) Area: Class Area stores per-class structures such as the runtime constant pool, field, method data, and the code for methods.
Heap: It is the runtime data area in which the memory is allocated to the objects
Stack: Java Stack stores frames. It holds local variables and partial results, and plays a part in method invocation and return. Each thread has a private JVM stack, created at the same time as the thread. A new frame is created each time a method is invoked. A frame is destroyed when its method invocation completes.
Program Counter Register: PC (program counter) register contains the address of the Java virtual machine instruction currently being executed.
Native Method Stack: It contains all the native methods used in the application. More Details.

What is JIT compiler? Just-In-Time(JIT) compiler: It is used to improve the performance. JIT compiles parts of the bytecode that have similar functionality at the same time, and hence reduces the amount of time needed for compilation. Here the term “compiler” refers to a translator from the instruction set of a Java virtual machine (JVM) to the instruction set of a specific CPU.

Yes, Java allows to save our java file by .java only, we need to compile it by javac .java and run by java classname Let's take a simple example:

//save by .java only
class A{
public static void main(String args[]){
System.out.println("Hello java");
}
}
//compile by javac .java
//run by java A compile it by javac .java run it by java A
1. Is delete, next, main, exit or null keyword in java? No.
2. If I don't provide any arguments on the command line, then what will the value stored in the String array passed into the main() method, empty or NULL? It is empty, but not null.
3. What if I write static public void instead of public static void? The program compiles and runs correctly because the order of specifiers doesn't matter in Java.
4. What is the default value of the local variables? The local variables are not initialized to any default value, neither primitives nor object references.
5. What are the various access specifiers in Java? In Java, access specifiers are the keywords which are used to define the access scope of the method, class, or a variable. In Java, there are four access specifiers given below.

o Public The classes, methods, or variables which are defined as public, can be accessed by any class or method. o Protected Protected can be accessed by the class of the same package, or by the sub- class of this class, or within the same class. o Default Default are accessible within the package only. By default, all the classes, methods, and variables are of default scope. o Private The private class, methods, or variables defined as private can be accessed within the class only.

What is the purpose of static methods and variables? The methods or variables defined as static are shared among all the objects of the class. The static is the part of the class and not of the object. The static variables are stored in the class area, and we do not need to create the object to access such variables. Therefore, static is used in the case, where we need to define variables or methods which are common to all the objects of the class. For example, In the class simulating the collection of the students in a college, the name of the college is the common attribute to all the students. Therefore, the college name will be defined as static.
What are the advantages of Packages in Java? There are various advantages of defining packages in Java. o Packages avoid the name clashes. o The Package provides easier access control. o We can also have the hidden classes that are not visible outside and used by the package. o It is easier to locate the related classes.
What is the output of the following Java program?

class Test
{
public static void main (String args[])
{
System.out.println( 10 + 20 + "Javatpoint");
System.out.println("Javatpoint" + 10 + 20 );
}
}

for(int i= 0 ; 0 ; i++)
{
System.out.println("Hello Javatpoint");
}
}
} The above code will give the compile-time error because the for loop demands a boolean value in the second part and we are providing an integer value, i.e., 0. Core Java - OOPs Concepts: Initial OOPs Interview Questions There is given more than 50 OOPs (Object-Oriented Programming and System) interview questions. However, they have been categorized in many sections such as constructor interview questions, static interview questions, Inheritance Interview questions, Abstraction interview question, Polymorphism interview questions, etc. for better understanding.
1. What is object-oriented paradigm? It is a programming paradigm based on objects having data and methods defined in the class to which it belongs. Object-oriented paradigm aims to incorporate the advantages of modularity and reusability. Objects are the instances of classes which interacts with one another to design applications and programs. There are the following features of the object- oriented paradigm. o Follows the bottom-up approach in program design. o Focus on data with methods to operate upon the object's data o Includes the concept like Encapsulation and abstraction which hides the complexities from the user and show only functionality. o Implements the real-time approach like inheritance, abstraction, etc. o The examples of the object-oriented paradigm are C++, Simula, Smalltalk, Python, C#, etc.
2. What is an object? The Object is the real-time entity having some state and behavior. In Java, Object is an instance of the class having the instance variables as the state of the object and the methods as the behavior of the object. The object of a class can be created by using the new keyword.

What is the difference between an object-oriented programming language and object- based programming language? There are the following basic differences between the object-oriented language and object- based language. o Object-oriented languages follow all the concepts of OOPs whereas, the object-based language doesn't follow all the concepts of OOPs like inheritance and polymorphism. o Object-oriented languages do not have the inbuilt objects whereas Object-based languages have the inbuilt objects, for example, JavaScript has window object. o Examples of object-oriented programming are Java, C#, Smalltalk, etc. whereas the examples of object-based languages are JavaScript, VBScript, etc.
What will be the initial value of an object reference which is defined as an instance variable? All object references are initialized to null in Java. Core Java - OOPs Concepts: Constructor Interview Questions
What is the constructor? The constructor can be defined as the special type of method that is used to initialize the state of an object. It is invoked when the class is instantiated, and the memory is allocated for the object. Every time, an object is created using the new keyword, the default constructor of the class is called. The name of the constructor must be similar to the class name. The constructor must not have an explicit return type. More Details.
How many types of constructors are used in Java? Based on the parameters passed in the constructors, there are two types of constructors in Java. o Default Constructor: default constructor is the one which does not accept any value. The default constructor is mainly used to initialize the instance variable with the default values. It can also be used for performing some useful task on object creation. A default constructor is invoked implicitly by the compiler if there is no constructor defined in the class.

Explanation: In the above class, you are not creating any constructor, so compiler provides you a default constructor. Here 0 and null values are provided by default constructor. More Details.

Does constructor return any value? Ans: yes, The constructor implicitly returns the current instance of the class (You can't use an explicit return type with the constructor). More Details. 31)Is constructor inherited? No, The constructor is not inherited.
Can you make a constructor final? No, the constructor can't be final.
Can we overload the constructors? Yes, the constructors can be overloaded by changing the number of arguments accepted by the constructor or by changing the data type of the parameters. Consider the following example.

class Test
{
int i;
public Test(int k)
{
i=k;
}

public Test(int k, int m)
{
System.out.println("Hi I am assigning the value max(k, m) to i");
if(k>m)
{
i=k;
}
else
{
i=m;
}
}
}
public class Main
{
public static void main (String args[])
{
Test test1 = new Test( 10 );
Test test2 = new Test( 12 , 15 );
System.out.println(test1.i);
System.out.println(test2.i);
}
}
In the above program, The constructor Test is overloaded with another constructor. In the first call to the constructor, The constructor with one argument is called, and i will be initialized with the value 10. However, In the second call to the constructor, The constructor with the 2 arguments is called, and i will be initialized with the value 15.
1. What do you understand by copy constructor in Java? There is no copy constructor in java. However, we can copy the values from one object to another like copy constructor in C++. There are many ways to copy the values of one object into another in java. They are: o By constructor o By assigning the values of one object into another o By clone() method of Object class In this example, we are going to copy the values of one object into another using java constructor.
//Java program to initialize the values from one object to another
class Student6{

The constructor name must be same as the class name. The method name may or may not be same as class name.

What is the output of the following Java program?

public class Test
{
Test(int a, int b)
{
System.out.println("a = "+a+" b = "+b);
}
Test(int a, float b)
{
System.out.println("a = "+a+" b = "+b);
}
public static void main (String args[])
{
byte a = 10 ;

byte b = 15 ;
Test test = new Test(a,b);
}
} The output of the following program is: a = 10 b = 15 Here, the data type of the variables a and b, i.e., byte gets promoted to int, and the first parameterized constructor with the two integer parameters is called.
1. What is the output of the following Java program?
class Test
{
int i;
}
public class Main
{
public static void main (String args[])
{
Test test = new Test();
System.out.println(test.i);
}
} The output of the program is 0 because the variable i is initialized to 0 internally. As we know that a default constructor is invoked implicitly if there is no constructor in the class, the variable i is initialized to 0 since there is no constructor in the class.
1. What is the output of the following Java program?
class Test
{
int test_a, test_b;
Test(int a, int b)
{
test_a = a;
test_b = b;
}
public static void main (String args[])
{
Test test = new Test();
System.out.println(test.test_a+" "+test.test_b);

More Details.

What is the static method? o A static method belongs to the class rather than the object. o There is no need to create the object to call the static methods. o A static method can access and change the value of the static variable. More Details.
What are the restrictions that are applied to the Java static methods? Two main restrictions are applied to the static methods. o The static method can not use non-static data member or call the non-static method directly. o this and super cannot be used in static context as they are non-static.
Why is the main method static? Because the object is not required to call the static method. If we make the main method non- static, JVM will have to create its object first and then call main() method which will lead to the extra memory allocation. More Details.

Can we override the static methods? No, we can't override static methods.
What is the static block? Static block is used to initialize the static data member. It is executed before the main method, at the time of classloading.

class A2{
static{System.out.println("static block is invoked");}
public static void main(String args[]){
System.out.println("Hello main");
}
} Test it Now Output: static block is invoked Hello main More Details.
1. Can we execute a program without main() method? Ans) Yes, one of the ways to execute the program without the main method is using static block. More Details.
2. What if the static modifier is removed from the signature of the main method? Program compiles. However, at runtime, It throws an error "NoSuchMethodError."
3. What is the difference between static (class) method and instance method? static or class method instance method 1)A method that is declared as static is known as the static method. A method that is not declared as static is known as the instance method. 2)We don't need to create the objects to call the static methods. The object is required to call the instance methods.

JAVA BASIC STRUCTURE NOTES, Exams of Java Programming

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JRE