How to compile packages in java?

Question

I have written a simple package program:

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  //A simple package         package MyPack          class Balance        {         String name;         double bal;          Balance(String n, double b)         {             name=n;                     bal=b;             }          void show()             {             if(bal<0)             System.out.println("-->");             System.out.println(name+ ": $:" +bal);         }         }          class AccountBalance         {             public static void main(String args[])             {                        Balance current[]=new Balance[3];                     current[0]=new Balance("A.K.Juwatkar",123.123);                     current[1]=new Balance("A.P.Dhoke",345.67);                     current[2]=new Balance("Anil Sarang",100.98);                      for(int i=0;i<3;i++)                 current[i].show();                }         } 

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I am using Ubuntu 10.04 & When i compile it using

java MyPack.AccountBalance 

I get the following message:

Exception in thread "main" java.lang.NoClassDefFoundError: MyPack/AccountBalance Caused by: java.lang.ClassNotFoundException: MyPack.AccountBalance     at java.net.URLClassLoader$1.run(URLClassLoader.java:217)     at java.security.AccessController.doPrivileged(Native Method)     at java.net.URLClassLoader.findClass(URLClassLoader.java:205)     at java.lang.ClassLoader.loadClass(ClassLoader.java:321)     at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)     at java.lang.ClassLoader.loadClass(ClassLoader.java:266) Could not find the main class: MyPack.AccountBalance. Program will exit. 

What is wrong? Please help me out. I have installed openjdk, do i need to install anything else?? I am using Ubuntu 10.04, kindly help me out

Answer 1

Best is to compile and run the classes from outside the packages :

First you compile with javac :

$javac MyPack/AccountBalance.java 

this will create a new file in the MyPack folder called AccountBalance.class

then you can run it :

$java MyPack.AccountBalance 

By the way: it is discouraged to have package names start with a capital.

Answer 2

When you are trying to compile the java class, use the '-d' option (destination) to specify where the .class files should be located.

javac -d "classes" AccountBalance.java 

and when you run your program, make sure that same folder is included in your class path:

java -classpath "classes" MyPack.AccountBalance