Question

In the code below, there is a bug. please write a test case to expose the bug?

NOTE: We assume empty stack is a proper behavior. this behavior is it is not a bug.

import java.util.ArrayList;

class Stack
{ private int count = 0;

private ArrayList stack = new ArrayList();
  
public void push( Object obj )
{ stack.add( count++, obj );
System.out.println(count);
}
public Object pop()
{ return stack.remove( --count );
}
public void push_many( Object[] obj )
{ for( int i = 0; i < obj.length; ++i )
push( obj[i] );
}

Answer 1

// do comment if any problem arises

// code

import java.util.ArrayList;

class Stack {

    private int count = 0;

    private ArrayList stack = new ArrayList();

    public void push(Object obj) {

        stack.add(count++, obj);

        System.out.println(count);

    }

    public Object pop() {

        return stack.remove(--count);

    }

    public void push_many(Object[] obj) {

        for (int i = 0; i < obj.length; ++i)

            push(obj[i]);

    }

    public static void main(String[] args) {

        Stack testing=new Stack();

        testing.push("fd");

        int a=(int)testing.pop();

    }

}

Output:

PS E:\fixer> java Stack Exception in thread "main" java.lang.ClassCastException: java.lang.String cannot be cast to java.lang. Integer at Stack.main(Cat.java:30)

Explanation:

This exception occurs due to use of raw arraylist, use string or int as template argument.