Simple newbish error, public classes should be in its own file?

[voidflux]

Hello everyone, i'm new to java, and i'm using the java 1.4 sdk SE compiler. I just copied and pasted this books source code to make sure I didn't make any typo's and it still brings up this error when i compile:

C:\TEST>javac count.java
count.java:31: class CountInstances is public, should be declared in a file name
d CountInstances.java
public class CountInstances {
       ^
1 error

Here's the code, all its doing is using the constructor to count the number of instances i've created.

public class CountInstances {
      private static int numInstances = 0;
 
      protected static int getNumInstances() {
          return numInstances;
      }
 
      private static void addInstance() {
          numInstances++;
     }

     CountInstances() {
         CountInstances.addInstance();
     }

     public static void main(String[] arguments) {
         System.out.println("Starting with " +
             CountInstances.getNumInstances() + " instances");
         for (int  i = 0; i < 10; ++i)
            new CountInstances();
         System.out.println("Created " +
            CountInstances.getNumInstances() + " instances");
    }
 }

THanks!


By the way when I take out the modifer public the code compiles fine, but why do I have to take the keyword public off the class? And why does this book suck so bad?

[Dillinger4]

A Java source file can contain more than one class definition. Sun's JDK enforces the rule that at most one class in the source file must have public accessibility. The name of this source file is the name of the public class with the .java extension. You will notice that when you compile a source file that contains multiple classes separate .class files will be created.

[ayan]

save the code to CountInstances.java

[voidflux]

i'm still alittle confused on why it brought up an error, and the file was already saved as a .java file. You said, at most one class in the source file must have public accessibility. So because the main function is , public static void main(.... it will give me a compiler error because its now seeing 2 different public function because I had the CountInstances as a public class also? Thanks for the responces.

[Dillinger4]

You seem to be confusing yourself. Your code runs fine as long as you name the .java class file after the public class you posted before.