Java Method with Enforced Array Size Parameters?

Question

I would like to create an initialisation method for a Java class that accepts 3 parameters:

Employee[] method( String[] employeeNames, Integer[] employeeAges         


        

Answer 1

Since the arrays being passed in aren't generated until runtime, it is not possible to prevent the method call from completing depending upon the characteristics of the array being passed in as a compile-time check.

As Jon Skeet has mentioned, the only way to indicate a problem is to throw an IllegalArgumentException or the like at runtime to stop the processing when the method is called with the wrong parameters.

In any case, the documentation should clearly note the expectations and the "contract" for using the method -- passing in of three arrays which have the same lengths. It would probably be a good idea to note this in the Javadocs for the method.

Answer 2

You can't enforce that at compile-time. You basically have to check it at execution time, and throw an exception if the constraint isn't met:

Employee[] method(String[] employeeNames,
                  Integer[] employeeAges,
                  float[] employeeSalaries)
{
    if (employeeNames == null
        || employeeAges == null 
        || employeeSalaries == null)
    {
        throw new NullPointerException();
    }
    int size = employeeNames.length;
    if (employeesAges.length != size || employeeSalaries.length != size)
    {
        throw new IllegalArgumentException
            ("Names/ages/salaries must be the same size");
    }
    ...
}

Answer 3

A way to skirt around the problem is to create a builder, e.g., EmployeeArrayBuilder,

public class EmployeeArrayBuilder {
   private Integer arraySize = null;
   private String[] employeeNames;
   public EmployeeArrayBuilder addName(String[] employeeNames) {
      if (arraySize == null) {
         arraySize = employeeNames.length;
      } else if (arraySize != employeeNames.length) {
         throw new IllegalArgumentException("employeeNames needs to be " + arraySize + " in length");
      }
      this.employeeNames = employeeNames;
      return this;
   }
   public EmployeeArrayBuilder addSalaries(float[] employeeSalaries) {/* similar to above */}
   public EmployeeArrayBuilder addAges(Integer[] employeeAges) {/* similar  */}
   public Employee[] build() {
       // here, you can do what you needed to do in the constructor in question, and be sure that the members are correctly sized.
       Employee myEmployees[] = new Employee[arraySize ];// dont know what size is            
       for ( int count = 0; count < arraySize ; count++) {
            myEmployees[count] = new Employee( employeeNames[count], employeeAges[count], employeeSalaries[count] );
       }
       return myEmployees;
   }
}