ArrayList<StringBuilder> al = new ArrayList<>(
Arrays.asList(new StringBuilder[]{
new StringBuilder("Oracle"),
new StringBuilder("Java"),
new StringBuilder("Sun"),
new StringBuilder("DataBase")}));
StringBuilder[] al2array = (StringBuilder[]) al.toArray();
If al.toArray() returns an Object[] which i know that its actually a StringBuilder[], then why cannot i cast it?
You most certainly can cast a variable typed as Object[] to one typed as StringBuilder[]. The compiler will not complain, and it will execute without error, IF the source reference does indeed reference a StringBuilder[].
public class ArrayCastTest {
public static void main(String[] argv) {
Object[] objArray;
StringBuilder[] sbArray;
objArray = getArray();
sbArray = (StringBuilder[]) objArray;
System.out.println(sbArray.toString());
}
public static Object[] getArray() {
return new StringBuilder[5];
}
}
This executes without error:
C:\JavaTools>javac ArrayCastTest.java
C:\JavaTools>java ArrayCastTest
[Ljava.lang.StringBuilder;@76f4da6d
C:\JavaTools>
The important thing to understand is that cast is "overloaded" -- it transforms simple values (like int to char) but it does not transform object references -- it only changes the declared type of the reference. The problem is that ArrayList.toArray() returns an Object[]. To get your Object[] into a StringBuilder[] use System.arraycopy.
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