CODEWITHSUNDEEP
java
Makoto
Makoto

Reputation: 775

var argument of lists as method argument

I have a unknown number of lists (two in my example but it can vary):

    SimpleDateFormat sdf = new SimpleDateFormat("yyyy, MM, dd");
    List<Employee> employees = new ArrayList<Employee>();
    employees.add(new Employee(100, "Abe Adams", sdf
            .parse("2009, 12, 1"), 10000.00));
    employees.add(new Employee(101, "Betty Barnes", sdf
            .parse("2010, 11, 1"), 11000.00));
    employees.add(new Employee(102, "Caleb Crown", sdf
            .parse("2011, 10, 1"), 12000.00));
    employees.add(new Employee(103, "Dirk Daniels", sdf
            .parse("2012, 09, 1"), 13000.00));

    Date date = new Date();
    List<ObjectTest> objects = new ArrayList<ObjectTest>();
    objects.add(new ObjectTest("name",date,10.0));
    objects.add(new ObjectTest("name2",date,20.0));

and I would like to use them as arg in a memthod

  oReport.writeReportToExcel(employees,objects);

with

   public <T> void writeReportToExcel(List <T> ... varArrayData  )    {
               ...
   }

I have to use var args parameters but the compiler rejects the code What needs to be changed ?

The message of the compiler is

method writeReportToExcel in class Bean2Excel cannot be applied to given types;
required: List<T>[]
found: List<Employee>, List<ObjectTest>
reason: inferred type does not conform to equality constraint(s)
inferred: ObjectTest
equality constraint(s): ObjectTest, Employee
where T is a type-variable:
T extends Object declared in method <T> wirteReportToExcel(List<T> ...)

EDIT FOR THE SOLUTION (it may be a dirty way)

    Bean2Excel oReport = new Bean2Excel();
    List recapList = new ArrayList();
    recapList.add(employees);
    recapList.add(objects);

    oReport.writeReportToExcel(recapList);

And as suggested I removed the generics

 public void writeReportToExcel(List datas)    {

    try {
        Bean2Excel oReport = new Bean2Excel();

        for (int i = 0;i<datas.size();i++){

            List data = (List)datas.get(i);
          ...
      }
}

Upvotes: 0

Views: 84

Answers (4)

james_wu_shanghai
james_wu_shanghai

Reputation: 56

<T> should be a specified type in a method. Employee or ObjectTest here, for example. But once you defined 2 different types in a method, and try to apply to List<T>[] named varArrayData, compile will refuse to do, for it cannot make sure T means Employee.class or ObjectTest.class.

If you really want to use var args, remove <T> mark in method signature might works:

public void writeReportToExcel(List ... varArrayData  )    {
           ...
}

Or you can put the type define to the class leave:

public class Bean2Excel<T>{


public void writeReportToExcel(List<T> ... varArrayData  )    {
           ...
   }
}

Hope it helps.

Upvotes: 1

kajacx
kajacx

Reputation: 12939

As said, i would create a common interface, let's say WritableToExcel or something, then use wildcards:

public void writeReportToExcel(List<? extends WritableToExcel>... varArrayData) { }

Now you can read from the lists inside your method, and call methods from WritableToExcel to write your table.

Upvotes: 1

NimChimpsky
NimChimpsky

Reputation: 47280

the arguments are of different types, T. You could remove the generic definition o rmake them implement a common interface.

Do you have to use var args ?

Upvotes: 2

Mattias Backman
Mattias Backman

Reputation: 957

Create a common base class for the types that can go in the lists.

If Employee and ObjectTest inherit from the same base class, it should work.

Upvotes: 0

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