class UserNameTest {
    public static void main(String[] args) {
        String name;
        name = System.getProperty("user.name");
        System.out.println(name);
    }
}

/*
"file.separator" File separator (for example, "/")  
"java.class.path" Java classpath 
"java.class.version" Java class version number 
"java.home" Java installation directory 
"java.vendor" Java vendor-specific string 
"java.vendor.url" Java vendor URL 
"java.version" Java version number 
  
"line.separator" Line separator 
  
"os.arch" Operating system architecture 
"os.name" Operating system name 
"os.version" Operating system version 
  
"path.separator" Path separator (for example, ":") 
  
"user.dir" User's current working directory 
"user.home" User home directory 
"user.name" User account name 

*/