Question

Is there a way to typecast from Java.lang.Object to an instance of a custom defined class.

Essentially, I have created a Stack (java.util.Stack) and have pushed into it instances of type my_class. But when I pop out from the Stack, I receive an instance of type Java.lang.Object.

Do I have to create a constructor in my_class that can create my_class instances from Java.lang.Object ?

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Generics is the best way to go. I am pretty new to Java, and without realizing about generics (same as in C++ STL), I have been doing a lot of typecasting like-

to convert to an integer: new Integer((Java.lang.Object).toString()).intValue()

Guess those days are gone now 🙂 Thanks for making my life easy.

Answer 1

You should write code using generics. For example instead of

MyObject someObj = ...;
Stack myStack = new Stack();
myStack.push(someObj);
someObj = myStack.pop(); // Error!

you can let the stack know about the type of object within:

MyObject someObj = ...;
Stack<MyObject> myStack = new Stack<MyObject>();
myStack.push(someObj);
someObj = myStack.pop(); // Now this works!

If for whatever reason this isn’t feasible, you can cast:

MyObject someObj = ...;
Stack myStack = new Stack();
myStack.push(someObj);
someObj = (MyObject) myStack.pop(); // This works too, but is considered very bad style