Problems with running java programs using CLR

thatanonymousgirl — Mon, 10 May 2021 05:29:13 +0000

Starting with Java?

Well, the first step as a newbie would be to install JDK - Java Development Kit. In earlier versions of JDK, there used to be a private JRE (Java Runtime Environment) as well as a public JRE as well. In later versions, the structure is changed, and we get only one folder of JDK, with private JRE. No Public JRE.
With the latest JDK version 16 in the market, one should still always go for the version which provides LTS - Long Time Support.
Currently, one should opt for Java SE 11 (LTS).

Now, Before running a program from the command line in java, things to be taken care of:

A. Set PATH variable in environment variables. It will tell the OS where the java executables like javac, java.exe are located. Set it to point JDK version/bin folder

B. Then, check if the classpath is set already?
Classpath will tell the java interpreter where to find java class file to run.
If it is not, leave it as it is. If it is already set to some value, make sure you add, current directory in that as well. Denote current directory by .;

C. To run a program from the command line, go to the source root folder and then run the execute java command along with a fully qualified package name. i.e., java com.rajnesh.MainClass

Like below:

Running it from anywhere else would throw this exception:

How Java program actually runs? What is Just in time compiler?

thatanonymousgirl — Sun, 04 Oct 2020 12:05:47 +0000

Java is a bit different from other types of compiled and interpreted languages.
First, a java program is compiled from source code to intermediate code called the byte code.
Java compiler does this job and javac command is used to invoke it.

This byte code is portable and can be run on any machine that has a machine specific JVM
installed on it. Now, JVM when triggered using the java command, will take line by line of this byte code and interpret it to machine code.
Here JIT comes into the picture. Even though it can optionally be disabled, it is a very useful part of JRE.

When JVM is invoked by the java command, the first thing it does is load the .class files at runtime
and then convert them into machine understandable code using an interpreter.
JIT Compiler when enabled, makes JVM analyze method calls in byte code, and if it sees any repeated code,
JIT compiles it to machine code the first time and replaces all the other occurrences directly with the machine code, hence saving a good amount of time.

Forem: thatanonymousgirl

Problems with running java programs using CLR

How Java program actually runs? What is Just in time compiler?