Re: typesafe java.util.Map construction and initialization

Thomas Hawtin <>
Wed, 20 Sep 2006 07:53:03 +0100
Josef Svitak wrote:

If I have:

public class foo {
  private interface BarIF { }
  private class BarImplOne implements BarIF { public BarImplOne() {} }
  private class BarImplTwo implements BarIF { public BarImplTwo() {} }

  private java.lang.String keys[] = { "key1", "key2" };
  private final bars[] = { new BarImplOne(), new BarImplTwo() };

  private final java.util.Map<String, BarIF> theMap;

  public foo() {
    // Can I do this... (doesn't work)
    theMap = new java.util.HashMap( keys, bars );

    // instead of this? (works)
    theMap.add( "key1", new BarImplOne() );

javac complains of not having a ctor for HashMap(String[], BarIF[]).

Yes, you can see that from the API docs.

You should be able to do is something like:

public class Foo {
     private interface Bar { }
     private class BarImplOne implements Bar { public BarImplOne() {} }
     private class BarImplTwo implements Bar { public BarImplTwo() {} }

     private final java.lang.String[] keys;
     private final Bar[] bars;

     private final java.util.Map<String, Bar> map;

     public Foo() {
         map = new java.util.LinkedHashMap<String, Bar>();
         map.put("key1", new BarImplOne());
         map.put("key2", new BarImplTwo());

         int num = map.size();
         keys = new String[num];
         bars = new Bar[num];

     public static void main(String[] args) {
         Foo foo = new Foo();


Or you can write your own method to construct a map from two arrays
(which I wouldn't really recommend).

Tom Hawtin
Unemployed English Java programmer

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