Java passes at the command prompt, but javac does not

I wanted to study an object-oriented language and tried to put Java in Windows. However, java passed, but javac did not.

$ javac
'javac'Is an internal or external command,
It is not recognized as an operable program or batch file.

When I check the folder where java.exe is installed It was written as "jre".

C:\Program Files (x86)\Java\jre1.8.0_191\bin

Therefore, I investigated jre by referring to the following site. https://furien.jp/columns/227/

According to this site Because jre ("Java Runtime Environment") is for running java I found that I couldn't write a program.

On the other hand If you install something called jdk ("Java Development Kit") It turns out that java can be developed.

Therefore, I reinstalled jdk according to the following article. https://eng-entrance.com/java-install-jdk-windows

Try compiling hello.java and running it.

hello.java

public class hello{
  public static void main(String[] args){
    System.out.print("Hello");
  }
}

I typed the following at the command prompt:

$ javac hello.java
$ java hello
Hello

As a result, it was executed normally. Congratulations. (It's short, but I'm sorry)