A rather silly one

[Angela Narain]

public class test
{
public static void main( String[] args )
{
int i = 3;
System.out.println(" From command line " + args.length); // works fine and prints 0
//int[] iArr;
//System.out.println(" Length of array " + iArr.length); // compile error - Array needs to be //initialized

Why does printing the length of the argument String[] args
not give any compile time error ?
While this is not the case with the local declared array iArr.

[Desai Sandeep]

Hi Anjela,
The String[] args of the main is initialized by the JVM.However, locally defined array needs to be initialized before you calculate its length.
Alternatively, you could declare the array as a class variable for compilation.However, still you will get RuntimeException, unless you initialize the array.
So the following code will compile but not run correctly :

<font size=+0><pre>
public class Test {
   
    private static int[] array;
 
    public static void main(String[] args) {
        System.out.println(array.length); //NullPointerException at runtime.
    }
}
</pre></font>

The following code will compile and run properly :

<font size=+0><pre>
public class Test {
   
    private static int[] array = new int[10];
 
    public static void main(String[] args) {
        System.out.println(array.length); // prints 10.
    }
}
</pre></font>

The following code will not compile :

<font size=+0><pre>
public class Test {
   
    public static void main(String[] args) {
        int[] array; 
        System.out.println(array.length); // the local variable should be initialized.
    }
}
</pre></font>

The following code will compile and run correctly

<font size=+0><pre>
public class Test {
   
    public static void main(String[] args) {
        int[] array = new int[20]; 
        System.out.println(array.length); // the local variable is initialized and hence the length 20 is printed in the output.
    }
}
</pre></font>

Hope this helps,
Sandeep
SCJP2, OCSD(Oracle JDeveloper), OCED(Oracle Internet Platform)