So, I have this class:
public class Product {
private String name, id, info ;
private int quantity;
public Product(String newName, String newID, String newInfo, Integer newQuantity){
setName(newName);
setID(newID);
setPrice(newInfo);
setQuantity(newQuantity);}
public void setName(String name) {
this.name = name; }
public void setID(String id) {
this.id = id; }
public void setPrice(String info) {
this.info = info; }
public void setQuantity(Integer quantity) {
this.quantity = quantity; }
public String getID( ) {
return id; }
public String getName( ) {
return name; }
public String getInfo( ) {
return info; }
public int getQuantity( ) {
return quantity; }
In another class i have this:
public class Invoice implements Group<Product> {
private HashMap<String, Product> prod = new HashMap<String, Product>( );
public Invoice(){ }
public void addProd(Product a) {
prod.put(??getID()??,new Product(??));
}
}
If this data was user generated rather than me, I would use the getID() method right?
So in my class invoice, how do i use the method getID(), so that I can use it in the parameter for my key value in the HashMap? Also is there a way to add 3 values (name info quan) to the hashmap without making a new class?
I see that you get Product object with ref "a" as parameter to your addProd method.
And you can get id by just using a.getID(). It should look as:
public void addProd(Product a) {
prod.put(a.getID(),a);
}
I didn't understand second part of your question.. I think you already have 3 values in your Product object and you put Product object to Map, So why do you require another way ?
Your class Product does not compile, because you have the name Item in your constructor. The constructor name must match the class name. So change that to Product. The same applies to Invoice vs ShoppingCart. Constructor and Class names must match.
As per your comment, you'd like to add four product values to a Map. The key being one of the values of the product itself. Try this:
Product p = new Product(name, id, info, quantity);
cart.addProd(p);
...
public void addProd(Product p) {
prod.put(p.getId(), p);
}
Maps can only map a single value to a single key, so you must have some sort of container for the values you wish to collate into one value. This can be an object (Product) or you could use a collection (e.g. List). I strongly recommend the former.
For your question about putting 3 values in your map, I don't think there's a way for you to put 3 values into one key without creating a class. An alternative is to store a Map<String, List<String>> assuming your 3 values are type String, or, Map<String, Map<String, String>>.
Related
public enum Dictionary {
PLACEHOLDER1 ("To be updated...", "Placeholder", "adjective"),
PLACEHOLDER2 ("To be updated...", "Placeholder", "adverb"),
PLACEHOLDER3 ("To be updated...", "Placeholder", "conjunction");
private String definition;
private String name;
private String partOfSpeech;
private Dictionary (String definition, String name, String partOfSpeech) {
this.definition = definition;
this.name = name;
this.partOfSpeech = partOfSpeech;
}
public String getName() {
return name;
}
public class DictionaryUser {
public static Dictionary getIfPresent(String name) {
return Enums.getIfPresent(Dictionary.class, name).orNull();
}
*public static Dictionary getIfPresent(String name) {
return Enums.getIfPresent(Dictionary.class, name.getName()).orNull();
}
I just recently came across getIfPresent() to basically have a global static map keyed on the Enum class name for lookup. The problem I have is instead, I would like to utilized my getter getName() for the lookup instead of by the name of the Enum name. In the example I have provided if the user typed in placeholder, all three values will show up. Is this achievable with my approach? I put a * next to my approach that does not work.
Since you need all matching objects but Enums.getIfPresent will give you only one object, you can easily achieve your goal by doing this :
public static Dictionary[] getIfPresent(String name)
{
List<Dictionary> response = new ArrayList<>( );
for(Dictionary d : Dictionary.values())
{
if( d.getName().equalsIgnoreCase( name ) )
{
response.add(d);
}
}
return response.size() > 0 ? response.toArray( new Dictionary[response.size()] ) : null;
}
I have a HashSet and a HashMap of Class. How to modify the class variable?
so I have a class Data, then I create HashSet of Data and HashMap of Data
then do population. later, I would like to modify the value name and number.
class Data {
private String name;
private int number;
public Data(String name, int number) {
this.name = name;
this.number = number;
}
public String toString() {
return name + ":" + number;
}
public void modifyNumber (int i) {
this.number+=i;
} }
public class Main {
public static void main(String[] args) {
Set<Data> dataSet = new LinkedHashSet<Data>();
Map<String, Data> map = new LinkedHashMap<String, Data>();
// I do the dataSet and map population, then do something else
//now I want to modify the value of name and number for HashSet and HashMap of Class
}}
create the getter and setter method for Data class
then get the object and change it
public void setName(String name){
this.name=name;
}
map.get("id").setName("newname");
map.get("id").modifyNumber(number);
To work inside a HashSet, the Data class should override equals and hashcode methods.
Otherwise the set will not operate as expected.
In your implementation you failed to override those methods.
But when you do that, you cannot change the attribute values which are used in equals and hashcode. This may cause the object to be in the wrong hash bucket for its new value.
You can change the other attributes.
hashset.iterator.next().setXXX();
Well, i was trying to pass arraylist of objects from one activity to another. I have 2 constructors in the class Student.
If, i use, Serializable than the code is like below:
#SuppressWarnings("serial")
public class Student implements Serializable
{
private int studentdID;
private String studentName;
private String studentDept;
public Student(){}
public Student(String name, String dpt)
{ this.studentName = name;
this.studentDept = dpt;}
public Student(int id, String name, String dpt)
{ this.studentdID = id;
this.studentName = name;
this.studentDept = dpt; }
public int getstudentdID() { return studentdID; }
public void setstudentdID(int studentdID) {this.studentdID = studentdID;}
public String getstudentName() { return studentName;}
public void setstudentName(String studentName) {this.studentName = studentName;}
public String getstudentDept() { return studentDept; }
public void setstudentDept(String studentDept) { this.studentDept = studentDept;}
}
But the problem i am facing is that how am i going to do this with parcelable? How am i going to set the values of the variables in class-like i did with Serializable? I mean separately using 2 constructors-one without ID another without the ID?
Did you read how Parcelable works?
You need only one constrcutor for parcelable to read what you pass to it, and Parcelable interface will add a method writeToParcel where you put the data to save.
It's not an automatic process like Serializable, everything is up to you.
The constructor which Parcelable will use will accept only one argument Parcel where you will find some methods like read*(KEY) to read back values.
And in writeToParcel you will write in the Parcel (the argument of the method) the values you want pass to pass with write*(KEY, VALUE).
Parcelable don't care about your constructors or fields.
P.S You will need a CREATOR too. Read some tutorial online to know more about it if you need.
Marco's answer explains why Parcelable doesn't automatically decide what constructor to use - it can't.
However, there is a way around this. Use Parcel.dataAvail(), which
Returns the amount of data remaining to be read from the parcel. That
is, dataSize()-dataPosition().
For example,
public Student(){}
public Student(String name, String dpt)
{
this.studentName = name;
this.studentDept = dpt;}
public Student(int id, String name, String dpt)
{ this.studentdID = id;
this.studentName = name;
this.studentDept = dpt;
}
public Student(Parcel in) {
name = in.readString();
dpt = in.readString();
if(in.dataAvail() > 0) // is there data left to read?
id = in.readInt();
}
^ The above constructor will allow for the necessary variables to be instantiated correctly. Also, you define writeToParcel() something like:
public void writeToParcel(Parcel out) {
out.writeString(name);
out.writeString(dpt);
//0 is the default value of id if you didn't initialize it like
// in the first constructor. If it isn't 0, that means it was initialized.
if(id != 0)
out.writeInt(id);
}
Of course, you'll need to define your CREATOR like so:
public static final Parcelable.Creator<Student> CREATOR = new Parcelable.Creator<Student>() {
public Student createFromParcel(Parcel in) {
return new Student(in);
}
public Student[] newArray(int size) {
return new Student[size];
}
};
#u3l solution is not required..how many constructors are there it doesn't matter.
simple it works go as normal implementation.
I mean no special care is required when multiple constructors present in parcelable.
I am attempting to create an inventory tracking system. I have a class (in Java) called "InventoryItem" with the properties of name and quantity.
This works fine for simple objects, but what if my inventory item contains other inventory items, for example, a server with RAM?
Should I be creating my own datatype, or is there a better way to do this (linked listed maybe)? should my class extend whatever that datatype is or should I not bother creating my own class?
My class so far:
public class InventoryItem {
private String name;
private int quantity;
private InventoryItem childInventoryItem;
// CONSTRUCTORS
public InventoryItem() {
}
public InventoryItem(int quantity, String name) {
this.quantity = quantity;
this.name = name;
}
//GETTERS
public String getName() {
return name;
}
public int getQuantity() {
return quantity;
}
//SETTERS
public void setName(String name) {
this.name = name;
}
public void setQuantity(int quantity) {
this.quantity = quantity;
}
}
A tree is usually what is involved in any parent-child relationship. If you aren't doing anything complicated, you can simply maintain an internal list that is basically List<InventoryItem> which contains any child items.
So all you would add to your class is something like this:
public class InventoryItem {
...
private List<InventoryItem> composingItems = new ArrayList<>(); //if still using Java 6 this must be new ArrayList<InventoryItem>();
...
public void addComposingItem(InventoryItem composingItem) {
composingItems.add(composingItems);
}
public List<InventoryItem> getComposingItems() {
//Enforce immutability so no one can mess with the collection. However
//this doesn't guarantee immutability for the objects inside the list;
//you will have to enforce that yourself.
return Collections.umodifiableList(composingItems);
}
}
There are many ways you can do this. I think the easiest way would be to create an array list.
ArrayList<InventoryItem> childInventory = new ArrayList<InventoryItem>();
Then create a setter that adds inventory items to this array
public void addChildItem(InventoryItem child)
childInventory.add(child);
This way you would have a list of all of the child items within the item. You could also make a method to return a list of all of the child items in either an array or an ArrayList.
public ArrayList<InventoryItem> getChildItems()
return childInventory;
I am trying to ensure that the objects i insert in productDatabase have not been already inserted and that i sort my arraylist using method sortData but without using any comparators in method sortData
public class Application {
public static void main(String[] args) {
Product p = new Product(15,"test",3.45);
Product p2 = new Product(15,"test",3.45);
Product p3 = new Product(4716,"koukouroukou",1.25);
Product p4 = new Product(6002,"bananofatsoula",0.60);
ProductDatabase productDatabase = new ProductDatabase();
productDatabase.addProduct(p);
productDatabase.addProduct(p2);
productDatabase.addProduct(p3);
productDatabase.addProduct(p4);
productDatabase.printDatabase();
productDatabase.sortDatabase();
productDatabase.printDatabase();
}
public class Product {
private int code;
private String name;
private double price;
public Product(int code, String name, double price){
this.code = code;
this.name = name;
this.price = price;
}
public int getCode() {
return code;
}
public void setCode(int code) {
this.code = code;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getPrice() {
return price;
}
public void setPrice(double price) {
this.price = price;
}
public String toString(){
return code+" , description: "+name+", price: "+price;
}
public int hashCode(){
return 31 * code + name.hashCode();
}
public boolean equals(Object o){
Product other = (Product)o;
if (this.code == other.code){
return true;
}
else{
return false;
}
}
import java.util.ArrayList;
import java.util.Collection;
public class ProductDatabase {
private ArrayList<Product> productDatabase;
public ProductDatabase(){
productDatabase = new ArrayList<Product>();
}
public void addProduct(Product p){
if(!productDatabase.contains(p)){
productDatabase.add(p);
}
}
public void printDatabase(){
for(Product product : productDatabase){
System.out.println(product);
}
}
public void sortDatabase(){
// ????????????????????????????????????????????????????????????
So my questions are
Does contain(p) is enough to ensure that the same product is not already in the list?
products are the same when they have the same code and name.if not what i have to do?
How i sort my withous using comparators in class ProductDatabase.maybe by a new method in product ?
Does productDatabase extends Product???
You can return bool value in order to know the product is already there or not . Code is used to ensure the differentiation of products if not add another code id.
Product instance will carry information of just one Product so Sort must be done in the member function of class having all the records of product, not just one.
No product_database does not extend product . It is a log of product class not a part .
your questions 1 and 2 are a little unclear. Can you re-write them? As for question 3. No ProductDatabase does not extend product, neither should it. ProductDatabase HAS products. ProductDatabase is not a product
Yes, contains() is enough (in our case) to ensure uniqueness
Since you implemented equals and hashCode - you're good
You don't need to sort if you don't have another purpose to do so, but since you're using an ArrayList every time contains() is called it iterates the whole list which is not very efficient. A better implementation would use Set (a HashSet for example)
ProductDatabase does not have to extend Product - it contains a list/set of products but it doesn't have any character/behavior like Product
Yes, contain(p) is enough to ensure that the same product is not already in the list, because you overrided "equals" method.
In "equals" you can use shorter construction:
Product other = (Product)o;
return this.code == other.code;
For sort ArrayList with java.util.Collections class two options possible:
Collections.sort(List list, Comparator c). You have to write own Comparator class and pass as second parameter.
Collections.sort(List list) and class Product must implement Comparable interface
Yes, Contain(p) is enough to ensure that the same product is not already in the list BUT that is NOT efficient. Use a Set instead of ArrayList.
For question 2, you have to decide the when the two products are equal and code that in your equals method like you did for 'product code'