117-implement-a-stack-

public class Stack {
    list<object> stk;
    public Stack(){
        this.stk = new list<object>(); 
    }
    public void push(Object obj) {
        //implement push
        stk.add(obj);
    }
    
    public Object pop() {
        //implement pop
        if(!stk.isEmpty()){
            object ob = stk.remove(stk.size()-1);
            return ob;
        }
        return null;
        
    }
    
    public Integer size() {
        //implement size
        return stk.size();
    }
    
    public Object peek(){
        //implement peek
        return stk[stk.size()-1];
    }
    
    public Boolean isEmpty() {
        //implement isEmpty
        return stk.isEmpty();
    }
}