Java program runs fine but doesn't compile

Question

I have a java program which runs properly.

But when I try to clean and build it in Netbeans it is choking on this line:

 protected HashMap<String, ArrayList<HashMap<String,String>>> config1

 config1 = new <String,ArrayList<HashMap<String,String>>> HashMap(); // build breaks here.

the error is:

  cannot find symbol  
  symbol  : constructor     
  <java.lang.String,java.util.ArrayList<java.util.HashMap<java.lang.String,java.lang.String>>
  >HashMap()

Answer 1

You are placing your type parameters in wrong place. It comes in between HashMap and the () : -

config1 = new HashMap<String,ArrayList<HashMap<String,String>>>();

---

Also, its a good idea to have more generalized types rather than specific types in the declaration, and even in generic type parameters . So you should use Map instead of HashMap in declaration, and List instead of ArrayList in your type parameter : -

And actually, you don't need to break your declaration and initialization in two lines. Just have them in one single line. It looks more cleaner. So, you can change your two lines to: -

protected Map<String, List<Map<String,String>>> config1 = 
                               new HashMap<String, List<Map<String,String>>>();

Answer 2

您必须将类名放在泛型之前。

config1 = new HashMap<String,ArrayList<HashMap<String,String>>>();

Answer 3

Generics should follow the class name. It should not be used before the class name. Correct your second line as below:

      protected HashMap<String, ArrayList<HashMap<String,String>>> config1;

      config1 = new HashMap <String,ArrayList<HashMap<String,String>>>();

Answer 4

你可以试试这个：

config1 = new  HashMap<String, ArrayList<HashMap<String, String>>>(); // build breaks here.