Core Java 1 Mark Questions Part 1

What is Java?

·         Java is an object-oriented programming language.

·         It is a high-level programming language developed by James Gosling in Sun Microsystem in 1995.

·         Java is a fast, secure and reliable language used for many games, devices and applications.

Differentiate between JDK, JRE and JVM.

·         JVM stands for Java Virtual Machine which provides runtime environment for Java Byte Codes to be executed.

·         JRE (Java Runtime Environment) that includes sets of files required by JVM during runtime.

·         JDK (Java Development Kit) consists of JRE along with the development tools required to write and execute a program.

What is IDE?

An Integrated Development Environment is a software application that provides comprehensive facilities to computer programmers for software development. An IDE normally consists of a source code editor, build automation tools and a debugger. Example Eclipse, NetBeans etc.

What is Class?

Class is a template that describes the data and behavior associated with instances of that class. A class is a user defined blueprint or prototype from which objects are created.

What is Object?

An Object is an Instance of Class. In real-world an entity that has state and its behavior is known as an object. For Example: A Car is an object. It has states (name, color, model) and its behavior (changing gear, applying brakes, runnin).

What is Data Encapsulation?

Encapsulation is a concept in Object Oriented Programming for combining properties and methods in a single unit.

Encapsulation helps programmers to follow a modular approach for software development as each object has its own set of methods and variables and serves its functions independent of other objects. Encapsulation also serves data hiding purpose.

What are Loops in Java? What are three types of loops?

Looping is used in programming to execute a statement or a block of statement repeatedly.

There are three types of loops in Java:

1) For Loops

For loops are used in java to execute statements repeatedly for a given number of times. For loops are used when number of times to execute the statements is known to programmer.

2) While Loops

While loop is used when certain statements need to be executed repeatedly until a condition is fulfilled. In while loops, condition is checked first before execution of statements.

3) Do While Loops

Do While Loop is same as While loop with only difference that condition is checked after execution of block of statements. Hence in case of do while loop, statements are executed at least once.

What are the two environment variables that must be set in order to run any Java programs?

Java programs can be executed in a machine only once following two environment variables have been properly set:

1.   PATH variable

2.   CLASSPATH variable

Can variables be used in Java without initialization?

In Java, if a variable is used in a code without prior initialization by a valid value, program doesn’t compile and gives an error as no default value is assigned to variables in Java.

What’s the base class in Java from which all classes are derived?

java.lang.object

What is Package in Java?

In Java, package is a collection of classes and interfaces which are bundled together as they are related to each other.

When the constructor of a class is invoked?

The constructor of a class is invoked every time an object is created with new keyword.

Can a class have multiple constructors?

Yes, a class can have multiple constructors with different parameters.

Is String a data type in java?

String is not a primitive data type in java. When a string is created in java, it’s actually an object of Java.Lang.String class that gets created. After creation of this string object, all built-in methods of String class can be used on the string object.

What’s the benefit of using inheritance?

Key benefit of using inheritance is reusability and extensibility of code

How can we restrict inheritance for a class so that no class can be inherited from it?

If we want a class not to be extended further by any class, we can use the keyword Final with the class name.

What are the access scopes of access specifiers in Java?

MODIFIER	CLASS	PACKAGE	SUBCLASS	WORLD
public	Y	Y	Y	Y
no modifier	Y	Y	N	N
protected	Y	Y	Y	N
private	Y	N	N	N

Can a class in Java be inherited from more than one class?

In Java, a class can be derived from only one class and not from multiple classes. Multiple inheritances are not supported by Java.

What’s the order of call of constructors in inheritance?

In case of inheritance, when a new object of a derived class is created, first the constructor of the super class is invoked and then the constructor of the derived class is invoked.

Is JDK required on each machine to run a Java program?

JDK is development Kit of Java and is required for development only and to run a Java program on a machine, JDK isn’t required. Only JRE is required.