CODEWITHSUNDEEP
java
Joe
Joe

Reputation: 2633

How to define integer variables for a generic class in java?

I have a short class:

public class Stack {

private int[] data;
private int Top;

Public Stack(int size) {

   data = new int[size];
   top = -1;

}

public void Push (int value) {

   top++;
   data[top] = value;

}

public int pop() {

   return data[top--];

}

public int top() {

   return data[top];

}

And i'm getting bunch of errors "cannot convert from int to T"... And also getting an error in the array definition of the constructor...

This is my code, i'm a beginner please help me to understand this:

public class Stack <T> {


    private T[] data;
    private T top;

    Public Stack(T size) {

    data = new T[size];// im getting error here "cannot create a generic array of T...
    top = -1; // what should I do with this?

    }

    public void Push (T value) {

    top++; //cannot convert from int to T
    data[top] = value; //cannot convert from int to T

    }

    public T pop() {

    return data[top--]; //cannot convert from int to T

    }

    public T top() {

    return data[top]; //cannot convert from int to T

   }

Upvotes: 1

Views: 78

Answers (2)

syme
syme

Reputation: 447

You did not say why you tried to convert all the "int"s to "T"s, but I can already say:

  • "public" (visibility of the constructor) should be without the capital.
  • Your variable "top" must be an int : whatever the type T, the variable top is an index.

  • You can not create a generic array. Instead of giving a size to the constructor, you should write the constructor to take an array of T.

    public class Stack<T> {

    private final T[] data;
    private int top;

    public Stack(final T[] data) {
        this.data = data;
        top = -1;
    }

    public void Push(final T value) {
        top++;
        data[top] = value;
    }

    public T pop() {
        return data[top--];
    }

    public T top() {
        return data[top];
    }
}

edit: I also added "final" to the field "data" because I always declare "final" everything I can.

Upvotes: 2

rgettman
rgettman

Reputation: 178253

Your top variable is meant to store an index into your array representing the top of the stack. It's not meant to store any actual data; it's just an index. Therefore, when making your Stack class generic, it should not be converted to type T. It should remain an int.

The parameter to your constructor, size, must be of type int also. As for creating generic arrays, please refer to How to: generic array creation.

Upvotes: 1

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