When you want to become a java developer, first you should know what is JDK, JRE and JVM. This blog is helpful for a beginner.
JVM stands for Java virtual machine, it runs on top of the system operating system. It will be acting as an operating system. It is a virtual machine that runs the java programs. The JVM can run the other programs which are written in other languages and compiled by the Java compiler. It is taking care of program execution by providing runtime environment and allocating some resources.
JRE stands for Java Runtime Environment. It holds Java runtime libraries (rt.jar) and also other libraries which are required by the JVM at runtime to run the Java programs. JRE holds the JVM, which means the JVM presented inside the JRE.
JDK stands for Java Development Kit. It provides development tools to develop the Java programs. That requires at the development time only not needed at runtime. Just JRE is sufficient to run the Java program. When you install the JDK it comes with JRE and JVM. In short word you can say JDK is a combination of JRE and JVM.