My assignment is to write a test program that prompts a user for 5 strings and displays them in reverse order using MyStack and ArrayList. I need help figuring out how to take user input and put it into the stack and print it in reverse.
MyStack Class
MyMain
My Main:
package arraylist;
import java.util.Scanner;
/**
*
* #author dghelardini
*/
public class ArrayList {
/**
* #param args the command line arguments
*/
public static void main(String[] args)
{
Scanner userIn = new Scanner(System.in);
System.out.print("Enter five names: ");
}
}
MyStack Class:
package arraylist;
/**
*
* #author dghelardini
*/
public class MyStack extends ArrayList
{
private ArrayList<Object> theList = new ArrayList<>();
public boolean isEmpty()
{
return theList.isEmpty();
}
public int getSize()
{
return theList.size();
}
public Object peek()
{
return theList.get(getSize()-1);
}
public Object pop()
{
Object o = theList.get(getSize()-1);
theList.remove(getSize()-1);
return o;
}
public void push(Object o)
{
theList.add(o);
}
#Override
public String toString()
{
return "stack:" + theList.toString();
}
}
Scanner:
http://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html?is-external=true
The user enters the string, then you call the stack to store the 5 strings. Then when you pop, the stack returns the last item that
Related
I'm trying to learn the Iterator design pattern in Java. Below is a code sample of the implementation of the iterator pattern.
public class IteratorDemo {
/**
* #param args the command line arguments
*/
public static void main(String[] args) {
NameRepository repo=new NameRepository();
for(Iterator iter=repo.getIterarter(); iter.hasNext();){
String name=(String) iter.next();
System.out.println("Name : "+name);
}
}
}
interface Container{
public Iterator getIterarter();
}
interface Iterator{
public boolean hasNext();
public Object next();
}
class NameRepository implements Container{
private String[] names={"A","B","C","D","E","F"};
#Override
public Iterator getIterarter() {
return new NameIterator();
}
private class NameIterator implements Iterator{
int index;
#Override
public boolean hasNext() {
return index < names.length;
}
#Override
public Object next() {
if(this.hasNext()){
return names[index++];
}
return null;
}
}
}
Here the output is A , B, C, D,E ,F. My question is how this for loop iterates to the next item ? As it seems there is no iterating value in the code, but still it prints out the whole array
See, index is increasing every time if index < names.length
**
#Override
public Object next() {
if(this.hasNext()){
return names[index++];
}
return null;
}
**
I'm pretty new to Java but I feel like this is an easy task. This arraylist has two elements...names and scores. I want to write a method that prints a list of all the names in the list, not the scores. I know I've done this before I just can't remember how lol
import java.util.ArrayList;
/**
* Print test scrose and student names as well as he average for the class.
*/
public class TestScores {
private ArrayList<Classroom> scores;
public int studentScores;
/**
* Create a new ArrayList of scores and add some scores
*/
public TestScores() {
scores = new ArrayList<Classroom>();
}
/**
* Add a new student and a new score.
*/
public void add (String name, int score) {
scores.add(new Classroom(name, score));
if(score > 100){
System.out.println("The score cannot be more than 100");
}
}
/**
* Return all the student names.
*/
public void printAllNames() {//this is the method.
for (Classroom s : scores){
System.out.println(scores.get(name));
}
}
}
and the classroom class:
import java.util.ArrayList;
/**
* This class creates the names and scores of the students
*/
public class Classroom {
public int score;
public String name;
/**
* Constructor for the Class that adds a name and a score.
*/
public Classroom(String aName, int aScore) {
score = aScore;
name = aName;
}
/**
* Return the name of the students
*/
public String returnName() {
return name;
}
/**
* Return he scores
*/
public int returnScore() {
return score;
}
}
public void printAllNames() {//this is the method.
for (Classroom s : scores){
System.out.println(s.returnName());
}
}
You should be precice in your question, your list does not contain 2 elements - names and scores - but multiple Classroom objects which contain names and scores.
Alternative answer using Java 8 streams:
scores.stream().map(c -> c.returnName()).forEach(System.out::println);
This is for homework.
I am making a stack using a linked list. I have chosen to use the linked list from Java's java.util.LinkedList package. When I call the addFirst() method in my Main class, the program won't finish. It acts like an infinite loop, but as far as I know there are no loops involved. Here is the code:
package assignment3;
import java.util.LinkedList;
/**
*
* #author Eric
*/
public class LinkedListStack<T> {
LinkedList linkedList = new LinkedList();
public boolean isEmpty() {
if (linkedList.isEmpty()) {
return true;
} else {
return false;
}
}
public int size() {
int size = linkedList.size();
System.out.println("The size of the stack is " + size);
return size;
}
// This is the problem method.
public void push(T element) {
linkedList.addFirst(element);
}
public void pop() {
while(!linkedList.isEmpty()){
linkedList.removeFirst();
}
}
public void peek() {
while(!linkedList.isEmpty()){
linkedList.peek();
}
System.out.println("The first element in the stack is " + linkedList.peek());
}
}
This is the class Main that calls the push() method.
package assignment3;
/**
*
* #author Eric
*/
public class Main {
public static void main(String args[]) {
LinkedListStack linkedListStack = new LinkedListStack();
linkedListStack.push(1); // This never finishes.
linkedListStack.peek();
linkedListStack.size();
}
}
It's very hard to test LinkedListStack.java because I cannot push anything onto the stack. I have no idea what's wrong.
while(!linkedList.isEmpty()){
linkedList.peek();
}
peek() will never change a linked list from nonempty to empty, since it doesn't change the list.
but as far as I know there are no loops involved
What do you think while is?
Is there any simple way to get the stack to display then empty itself inside the method "PrintAndEmpty"? I need the print and empty inside the method PrintAndEmpty and not the main. The codes are:
import java.util.*;
class Stack<E> implements StackInterface<E> {
private ArrayList<E> items;
public Stack() { // default constructor; creates an empty stack
items = new ArrayList<E>(); // initial capacity is 10
}
public Stack(int initialCapacity) {
//one argument constructor, creates a stack with initial capacity initialCapacity
items = new ArrayList<E>(initialCapacity);
}
public void push(E x) {
items.add(x); //uses the ArrayList method add(E o)
}
public E pop() {
if (empty()) // determine whether or not there is an item to remove
return null;
return items.remove(items.size()-1); //uses the ArrayList method remove(int n)
}
public boolean empty() {
return items.isEmpty();//uses the ArrayList method isEmpty()
}
public int size() {
return items.size(); //uses the ArayList method size()
}
public E peek() {
if (empty()) // determine whether or not there is an item on the stack
return null;
return items.get(items.size()-1); //uses the ArrayList method get(int i)
}
public void PrintAndEmpty()
{
// I want to print then empty the stack here, not in the main method.
}
Main method
public static void main (String[] args) // for demonstration only
{
Stack<Student> s = new Stack<Student>();
// push five Student references onto s
s.push(new Student("Spanky", "1245"));
s.push(new Student("Alfalfa", "1656"));
s.push(new Student("Darla", " 6525"));
s.push(new Student("Stimie", "1235"));
s.push(new Student("Jackie", "3498"));
// The data below is what I am trying to put in the PrintAndEmpty method
while(!s.empty())
System.out.println(s.pop().getName());
System.out.println();
System.out.println("The size of the stack is now "+s.size());
}
The Student Class for testing purposes:
public class Student
{
private String name;
private String id;
public Student()
{
name = "";
id = "";
}
public Student (String n, String idNum)
{
name = n;
id = idNum;
}
public String getName()
{
return name;
}
public String getID()
{
return id;
}
public void setName(String n)
{
name = n;
}
public void setID( String idNum)
{
id = idNum;
}
public boolean equals(Object o) // name and id are the same
{
return ( (((Student)o).name).equals(name) &&
(((Student)o).id).equals(id) );
}
}
I am all out of ideas as far as getting this to work. If anyone has suggestions, please let me know. I would greatly appreciate it!
Not sure why you'd want to do that, but here is how you would do it:
// PrintAndEmpty 'this' stack.
public void PrintAndEmpty()
{
// The condition to check - e.g. 'this' stack.
while(!this.empty()) {
// Pop from the stack - e.g. 'this' stack.
System.out.println(this.pop().getName());
}
}
I want to create several objects from a class in a for loop. but I don't know how to code it. What I have written creates a new object but it overwrites the previous object.
package assginment1_version4;
import java.util.*;
public class Client {
public static void main (String[] args) {
System.out.println ("this is a bill database");
System.out.println ("add a user?(Y/N)");
Scanner input = new Scanner(System.in);
String answer = input.nextLine ();
ArrayList ary = new ArrayList ();
for (int i=1 ; i < 100; i++) {
if (answer.equalsIgnoreCase("y")) {
Bill bill1 = new Bill();
System.out.println("user first name:");
bill1.setFname (input.nextLine());
System.out.println("user Last name:");
bill1.setLname (input.nextLine());
System.out.println ("add a user?(Y/N)");
answer = input.nextLine ();
} else if (answer.equalsIgnoreCase ("n")) {
if (Bill.getBillCounter () == 0) {
System.out.println ("the Database is empty");
break;
} else {
System.out.println ("Number of Users: "
+ Bill.getBillCounter ());
break;
}
} else {
while (!answer.equalsIgnoreCase ("n")
&& !answer.equalsIgnoreCase ("y")) {
System.out.println ("add a user?(Y/N)");
answer = input.nextLine ();
}
}
}
}
}
please help me to complete this code.
You're overriding them because you create a new Bill on each loop and never save them off anywhere. I believe you want to add them to your ArrayList:
First, you should add a type to your ArrayList:
ArrayList<Bill> ary = new ArrayList<Bill>();
Then, before you get the input from the user on whether or not to add a new Bill, you should add the current one to this list:
...
System.out.println("user Last name:");
bill1.setLname(input.nextLine());
ary.add(bill1);
...
You haven't used the ArrayList, you need to add the Bill's objects at the end of the for loop.
ary.add(bill1);
and add a type to your ArrayList
ArrayList<Bill> ary = new ArrayList<Bill>();
This is the Bill class.....
package assginment1_version2;
public class Bill {
/**
* Attributes of a bill
*/
private String firstName;
private String lastName;
private int paymentDeadline;
private int paymentCode;
private int billCode;
/**
* Attribute of Bill Class
*/
private static int BillCounter=0;
/**
* Methods of Bill class
* #return number of users
*/
/*public static int getBillCounter(){
return BillCounter;
}*/
/**
* Class Constructor
* #param Fname is the first name of user
* #param Lname is the last name of user
* #param Pdeadline is the deadline of paying the bill
* #param Pcode introduces the payment uniquely
* #param Bcode introduces the bill uniquely
*/
public Bill (){
BillCounter++;
}
/**
* FirstName methods
* method to set FirstName
* #param n is the input of setname method as a user name
*/
public void setFname (String n){
firstName=n;
}
// method to get FirstName
public String getFname (){
return firstName;
}
/**
* LastName methods
* method to set LastName
*/
public void setLname (String m){
lastName=m;
}
// method to get LastName
public String getLname(){
return lastName;
}
/**
* PaymentDeadline methods
* method to set PaymentDeadline
*/
public void setPaymentDeadline(int m){
paymentDeadline= m;
}
//method to get PaymentDeadline
public int getPaymentDeadline(){
return paymentDeadline;
}
/*
* PaymentCode methods
* Method to set PaymentCode
*/
public void setPaymentCode (int m){
paymentCode=m;
}
//method to get PaymentCode
public int getPaymentCode(){
return paymentCode;
}
/*
* Methods of BillCode
* method to set BillCode
*/
public void setBcode(int Bcode){
billCode=Bcode;
}
//method to get BillCode
public int getBcode(){
return billCode;
}
}