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A. Core Java
1. What are the important features of Java 8 release?
Java 8 has been released in March 2014, so it’s one of the hot topic in java interview
questions. If you answer this question clearly, it will show that you like to keep yourself
up-to-date with the latest technologies.
Java 8 has been one of the biggest release after Java 5 annotations and generics. Some of
the important features of Java 8 are:
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
I strongly recommend to go through above links to get proper understanding of each one
of them, also read Java 8 Features.
2. 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.
3. 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. We can
customize JVM with Java Options, such as allocating minimum and maximum memory to
JVM. It’s called virtual because it provides an interface that doesn’t depend on the
underlying OS.
4. 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.
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5. 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.
6. 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.
7. Why Java doesn’t support multiple inheritance?
Java doesn’t support multiple inheritance in classes because of “Diamond Problem”. To
know more about diamond problem with example, read Multiple Inheritance in Java.
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. So there is no issue of diamond problem with interfaces.
8. 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.
Obviously java could have wrapper objects for the primitive types but just for the
representation, they would not have provided any benefit.
As we know, for all the primitive types we have wrapper classes such as Integer, Long etc
that provides some additional methods.
9. 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. If you work on Windows OS, read this
post to learn how to setup PATH variable on Windows.
Classpath is specific to java and used by java executables to locate class files. We can
provide the classpath location while running java application and it can be a directory, ZIP
files, JAR files etc.
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