查看“Java Hello”的源代码

JavaHello.java
* udf/IUdfHello.java
* udf/UdfHello.java

编译
 javac JavaHello.java

执行
 java JavaHello


====JavaHello.java====
 import udf.UdfHello;
 
 public class JavaHello extends UdfHello{
     public static final String INFO = "This is a test.";
 
     public static void main(String args[]) {
         JavaHello test1 = new JavaHello();
         test1.info();
         UdfHello test2 = new UdfHello("Hello, Java!", 1.1);
         test2.info();
         UdfHello test3 = new UdfHello("Hello!", 0.1);
         test3.info();
 
         System.out.println(test1.INFO);
         System.out.println(test3.VERSION);
     }
 }

====IUdfHello.java====
 package udf;
 
 public interface IUdfHello {
     public void info();
 }

====UdfHello.java====
 package udf;
 
 /*
 ------------------------------------------------------------------------------
   Name     : UdfHello
   Purpose  : Java Sample
   Author   : Adam
   Revisions:
   Ver        Date        Author           Description
   ---------  ----------  ---------------  ------------------------------------
   1.0        2024/1/22   Adam             My first Java program.
   1.1        2024/1/22   Adam             M01: comments & Spaces/CR/LF of code do not affect the compilation result
 
  format:
     object  : (), (string, double)
     property: VERSION
     method  : info
 ------------------------------------------------------------------------------
 */
 public class UdfHello implements IUdfHello {
     // private static final String Version = "v1.0";
     public static final String VERSION = "v1.0";
     private double Version = 1.0;
     private String INFO;
 
     // constructor with no parameter
     public UdfHello() {
         INFO = "Hello, World!";
     }
 
     // constructor & parameter
     public UdfHello(String info, double ver) {
         System.out.println("Variable: info=" + info + ", ver=" + ver);
         try {
             INFO = info;
             Version = ver > Version ? ver : Version;
             // Error: error: cannot assign a value to final variable VERSION  // M01:
             //  VERSION = "v1.1";
         }
         catch(Exception e) {
             System.out.println(e);
         }
 
     }
 
     public void info() {
         System.out.println("VERSION: " + VERSION);
         System.out.println("Ver: v"    + Version);      // M01:
         System.out.println(INFO);
         System.out.println("");
     }
 }