Simple loop iteration over Eclipse Collections maps (for example: IntObjectHashMap)

Question

Is there a way to use simple Java for-each loop over Eclipse Collections maps?

I am looking for something like this (but for Eclipse Collections maps):

for (Map.Entry<Integer, String> entry : map.entrySet()) {
}

... but I can't find anything like it for Eclipse Collections maps.

Of course I know this type of Eclipse Collections iterations:

import org.eclipse.collections.impl.map.mutable.primitive.IntObjectHashMap;

public class Test {
    public static void main(String[] args) {
        IntObjectHashMap<String> map = new IntObjectHashMap<>();
        map.put(1, "one");
        map.put(2, "two");
        int i = 0;
        map.forEachKeyValue((int key, String val) -> {
            i++; // Compilation error. 
            System.out.println("key: " + key + ", val: " + val);
        });
    }
}

... but this construct has some drawbacks, for example I don't have easy access to the surrounding local variables (as shown in the example above, which example will not compile due to incorrect access to the local variable i).

Any ideas how to write simple loop over Eclipse Collections maps?

I haven't used eclipse collections yet, but from the docs it would seel that [IntObjectHashMap.keyValuesView()](https://www.eclipse.org/collections/javadoc/9.2.0/org/eclipse/collections/impl/map/mutable/primitive/IntObjectHashMap.html#keyValuesView--) returns an Iterable over the Entries in the Map (as `IntObjectPair`-instances, in that case). It should be possible to use that in an enhanced for loop. — Hulk, Jan 27 '21 at 17:04
Doc: [*Map iteration methods*](https://github.com/eclipse/eclipse-collections/blob/master/docs/guide.md#-map-iteration-methods) — Basil Bourque, Jan 27 '21 at 18:24

Donald Raab · Answer 1 · 2021-01-29T15:59:47.320

The recommendations from Hulk and Basil in the comments are good. I'll include a test for your code that works for future reference.

@Test
public void keyValuesView()
{
    IntObjectHashMap<String> map = new IntObjectHashMap<>();
    map.put(1, "one");
    map.put(2, "two");
    int i = 0;
    for (IntObjectPair<String> pair : map.keyValuesView())
    {
        i++;
        System.out.println("key: " + pair.getOne() + ", val: " + pair.getTwo());
    }
    Assert.assertEquals(2, i);
}

The best option is to use an internal iterator as you have in your question, as there will be less garbage generated while iterating (an IntObjectPair for each key/value pair). This comes with the downside of not being able to reference anything from the outer scope of the lambda that is not final. If you want to have a simple counter for things inside of the internal iterator, you can use the Counter class available in Eclipse Collections.

@Test
public void forEachKeyValueWithCounter()
{
    IntObjectHashMap<String> map = new IntObjectHashMap<>();
    map.put(1, "one");
    map.put(2, "two");
    Counter counter = new Counter();
    map.forEachKeyValue((int key, String val) -> {
        counter.increment();
        System.out.println("key: " + key + ", val: " + val);
    });
    Assert.assertEquals(2, counter.getCount());
}

Simple loop iteration over Eclipse Collections maps (for example: IntObjectHashMap)

1 Answers1