JAVA TEST QA

What are the important features of Java 8 release?

1. Interface changes with default and static methods 2. Functional interfaces and Lambda Expressions 3. Java Stream API for collection classes 4. Java Date Time API

What is the difference between JDK and JVM?

Java Development Kit (JDK) is for development purpose and JVM is a part of it to execute the java programs. JDK provides all the tools, executables and binaries required to compile, debug and execute a Java Program. The execution part is handled by JVM to provide machine independence.

What is the difference between JVM and JRE?

Java Runtime Environment (JRE) is the implementation of JVM. JRE consists of JVM and java binaries and other classes to execute any program successfully. JRE doesn't contain any development tools like java compiler, debugger etc. If you want to execute any java program, you should have JRE installed.

What is JVM and is it platform independent?

Java Virtual Machine (JVM) is the heart of java programming language. JVM is responsible for converting byte code into machine readable code. JVM is not platform independent, thats why you have different JVM for different operating systems.

Why Java doesn't support multiple inheritance?

Java doesn't support multiple inheritance in classes because of "Diamond Problem". However multiple inheritance is supported in interfaces. An interface can extend multiple interfaces because they just declare the methods and implementation will be present in the implementing class.

Why Java is not pure Object Oriented language?

Java is not said to be pure object oriented because it support primitive types such as int, byte, short, long etc. I believe it brings simplicity to the language while writing our code.

What is Java Package and which package is imported by default?

Java package is the mechanism to organize the java classes by grouping them. java.lang package is imported by default and we don't need to import any class from this package explicitly.

What are access modifiers?

Java provides access control through public, private and protected access modifier keywords. When none of these are used, it's called default access modifier.

What is difference between path and classpath variables?

PATH is an environment variable used by operating system to locate the executables. That's why when we install Java or want any executable to be found by OS, we need to add the directory location in the PATH variable.

What do you mean by platform independence of Java?

Platform independence means that you can run the same Java Program in any Operating System. For example, you can write java program in Windows and run it in Mac OS.

Can we have multiple public classes in a java source file?

We can't have more than one public class in a single java source file. A single source file can have multiple classes that are not public.

What is overloading and overriding in java?

When we have more than one method with same name in a single class but the arguments are different, then it is called as method overloading. Overriding concept comes in picture with inheritance when we have two methods with same signature, one in parent class and another in child class.

Can we overload main method?

Yes, we can have multiple methods with name "main" in a single class. However if we run the class, java runtime environment will look for main method with syntax as public static void main(String args[]).

Which class is the superclass of all classes?

java.lang.Object is the root class for all the java classes and we don't need to extend it.

What is the importance of main method in Java?

main() method is the entry point of any standalone java application. The syntax of main method is public static void main(String args[]).