Casting an array

[Harsh Pensi]

 
        Number n = 1;
        Integer i = (Integer)n;//Compiles and runs fine.
    	
    	Number[] na = {1,2,3};
    	Integer[] ia = (Integer[])na;//ClassCastException at runtime
   

Why is the exception thrown?

[Deepak Bala]

This code snippet should help

  
	private void arrayTest()
	{
		Number[] na = {1,2,3};
		Integer[] ia = {1};
		String numberName = na.getClass().getName();
		String intName = ia.getClass().getName();
		Integer i=1;
		Number n = i;
		String iName = i.getClass().getName();
		String nName = n.getClass().getName();
		System.out.println(numberName + " " + intName);
		System.out.println(iName + " " + nName);
		System.out.println(ia instanceof Number[]);
		System.out.println(i instanceof Number);
	}
  

[Harsh Pensi]

So you're saying that since runtime class of Number[] na in the code is [Ljava.lang.Number we cannot cast it to Integer[]. Which is corrected by this code:

        Number[] na = new Integer[]{1,2,3};
    	Integer[] ia = (Integer[])na;//compiles and runs fine   

But what about following code:

        Object[] oa = new String[]{"1","2","3"};
    	System.out.println(oa.getClass().getName());//prints [Ljava.lang.String;
    	String[] sa1 = (String[])oa; //ClassCastException 

Since the runtime class of oa is [Ljava.lang.String; shouldnt we be able to cast it to String[] ?

[Deepak Bala]

Harsh Pensi wrote:So you're saying that since runtime class of Number[] na in the code is [Ljava.lang.Number we cannot cast it to Integer[]. Which is corrected by this code:

        Number[] na = new Integer[]{1,2,3};
    	Integer[] ia = (Integer[])na;//compiles and runs fine   

But what about following code:

        Object[] oa = new String[]{"1","2","3"};
    	System.out.println(oa.getClass().getName());//prints [Ljava.lang.String;
    	String[] sa1 = (String[])oa; //ClassCastException 

Since the runtime class of oa is [Ljava.lang.String; shouldnt we be able to cast it to String[] ?

I am able to do it without a RuntimeException

  		 Object[] oa = new String[]{"1","2","3"};  
		 String[] sa1 = (String[])oa;
		 System.out.println(sa1.length);  

Outputs 3. Do you see a different result ?

[Deepak Bala]

I am using JDK_1_6_06 under Win XP 64 bit

[Harsh Pensi]

Thanks for the replies. I guess my RAD is just playing with me. It is giving Exception on this line if I have more code below if not its running fine.

[Salil Vverma]

Hey Harsh,

This issue does not look me like of RAD region being I executed the code using the command line/eclipse in java 5 and I also got the class cast exception at run time.

 

public static void main(String[] args) {
		Number[] na = { 1, 2, 3 };
		Integer[] ia = (Integer[]) na;// ClassCastException at runtime
		System.out.println(java.util.Arrays.asList(ia));

	}
   

I guess, the root cause is something else. Can it be running in some of our friends machine just because they have java 6 rather than java5. Btw if you tweak the code a bit number to integer casting works fine. The below code works fine

   

	public static void main(String[] args) {

		Integer[] ia1 = { 1, 2, 3 };
		Number[] na1 = ia1;
		Integer[] ia2 = (Integer[]) na1;// Runs fine in java 5.0 from eclipse and command line both
		System.out.println(java.util.Arrays.asList(ia2));

	}

 

Regards
Salil Verma

[Ninad Kulkarni]

See the code below

public class EvaluationOrder{
	public static void main(String[] args){
		Number[] numArr = {1,2,3};
		Integer[] intArr = {1,2,3};
//		numArr = intArr;
		intArr = (Integer[])numArr;
	}
}

The code given above will compiles but throws runtime exception but if you remove comment on line number 5 then the above code will compiles and runs fine.
after line number 5 actual super class reference refer to sub class object so casting to Integer[] successfull at runtime but when super class reference refer to object of itself (that is commenting line number 5) then casting at line number 6 throws exception at runtime.