我需要使用for循环的方法的帮助

Question

  public void collect( int ordNum )
  {
       Basket b = new Basket(ordNum);
       for (Basket b : conveyerBelt) { // line 4
           readyCollected.add(b);
       }
  }

What I'm trying to do with this method is search through an ArrayList for a orderNum. When I find it, I want to add the orderNum i entered in to the readyCollected. Problem: I get an error message on line 4.

Was wondering if you can guys can help me implement this method.

BTW, the conveyerBelt already contains Basket with an order number. So lets say the conveyerBelt contains Basket with order number 3, and I enter in 3, I want it to add Basket to Arraylist readyCollected containing order number 3.

Answer 1

I'm guessing your error is that conveyerBelt is not Iterable. To use the foreach construct, you must make sure the object you are Iterating over implements Iterable.

http://java.sun.com/docs/books/jls/third_edition/html/statements.html#14.14.2

Excerpt:

The Expression must either have type Iterable or else it must be of an array type (§10.1), or a compile-time error occurs.

The scope of a local variable declared in the FormalParameter part of an enhanced for statement (§14.14) is the contained Statement

The meaning of the enhanced for statement is given by translation into a basic for statement.

If the type of Expression is a subtype of Iterable , then let I be the type of the expression Expression.iterator() . The enhanced for statement is equivalent to a basic for statement of the form:

for (I #i = Expression.iterator(); #i.hasNext(); ) {

        VariableModifiersopt Type Identifier = #i.next();
   Statement
}

Answer 2

You don't give nearly enough information to solve this properly.

• What is the error?
• What types are conveyerBelt and readyCollected?

Also what do you mean by "order number" - the Nth item in the list or is it some field?

Answer 3

conveyerBelt应被声明为Collection<Basket >通过Collection我的意思是任何Collection

Answer 4

Is it a compile error? Maybe something about a symbol and conveyerBelt ? Because it's not defined in the snippet you've given us.

Answer 5

You are using the same name ( b ) for two variables. That's probably the cause of the error you get, but I am not sure what you are trying to achieve with that code.

Answer 6

I think it's something like

public void collect( int ordNum )
{
    for (Basket b : conveyerBelt) {
        if (b.getOrdNum() == ordNum) {
            readyCollected.add(b);
            return;  // if only one occurrence wanted
        }
    }
}

assuming conveyerBelt is some Collection of Basket and readyCollected is some List of Basket .