CODEWITHSUNDEEP
javaobjectarraylistjava-7
cjm
cjm

Reputation: 844

Why is int being passed as Object?

import java.util.ArrayList;

class Stack {
    private ArrayList stack;
    private int pos;

    Stack() {
        stack = new ArrayList();
        pos = -1;
    }
    int pop() {
        if(pos < 0) {
             System.out.println("Stack underflow.");
             return 0;
        }
        int out = stack.get(pos);
        stack.remove(pos);
        pos--;
        return out;
    }
}

I am trying to write a basic variable length stack and this is a snippet of my code. When I run this, I get an error:

Main.java:16: error: incompatible types
   int out = stack.get(pos);
                       ^
required: int
found:    Object

Why is this being passed as an object?

Upvotes: 0

Views: 112

Answers (3)

Reimeus
Reimeus

Reputation: 159754

Currently you are not defining generic types held in your ArrayList called stack so you will get a raw Object return type from ArrayList.get:

You need to replace 

ArrayList stack;

with 

ArrayList<Integer> stack;

and similarly

stack = new ArrayList();

with 

stack = new ArrayList<Integer>(); // new ArrayList<>(); for Java 7

Also have a look at using java.util.Stack

Upvotes: 3

Jj Tuibeo
Jj Tuibeo

Reputation: 773

The stack.get(int) method returns an object. The int here is just the index. If you want to get the value of your stack at index int and it returns an Integer you need to do this:

Integer x = stack.get([int index position]);

Upvotes: 1

Foggzie
Foggzie

Reputation: 9821

stack wasn't informed of what variable type it holds so it resorts to the generic Object.

ArrayList stack;

should be

ArrayList<Integer> stack;

Upvotes: 1

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