Thread: Casting Confusion

Here is a simplified case of my problem. In the real world the Object is a two-dimensional array with dissimilar object types so I can't just make it an array of ArrayList.

import java.util.ArrayList;
 
public class Test {
 
	Object o = new ArrayList<String>();
 
	public Test() {
		ArrayList<String> l = (ArrayList<String>)o;
	}
 
	public static void main(String[] main) {
		new Test();
	}
}

The compiler (J2SE 1.7.0-b147) complains:


Test.java:8: warning: [unchecked] unchecked cast
ArrayList<String> l = (ArrayList<String>)o;
^
required: ArrayList<String>
found: Object
1 warning


How can I fix this warning?
Your recommendations will be appreciated.

p.s. The caret in the warning actually points to the object reference at the end of the line.

Thanks helloworld922 but that doesn't solve my problem. The instanceof operator is evaluated at runtime and my problem is a compiler warning. What I need is the correct cast syntax.

I get the impression that you're using parallel arrays to store data rather than creating a class to organize the data in an OOP way. Parallel arrays are to be avoided whenever possible in favor of a more OOP approach.

Your 2D array of dissimilar types could be modified to be an array (or ArrayList) of a single type with the single type containing the dissimilar types as fields:

public class MyDissimilarData
{
    // instance variables
    Type1 data1;
    Type2 data2;
 
    // constructor
    public MyDissimilarData( Type1 data1, Type2 data2 )
    {
        // etc . . . 
    }
 
    //  etc . . . . 
}