How can I change the apparent type to a real type in Java?

for example : 

public static String s(Object o)
    return o;

this method doesn't work/compile. To solve it I can write return o.toString() but I don't want that. I want to change the apparent type of o which is Object to the real type of o which is I know it is String.
How can I do that? I know there is a command that I can use it but I forget it. Anyone know it?

Thank you

Jon Skeet
people
quotationmark

It sounds like you're just after a cast:

public static String castToString(Object o) {
    return (String) o;
}

This will throw a ClassCastException if o is a non-null reference to a non-String type. (If o is a null reference, the cast will succeed and the result will still be a null reference.)

See JLS section 5.5 for more details.

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