How to call a method from another class in Java

问题:

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?

回答1:

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 ?

回答2:

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.

回答3:

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>>.