EC by Example: Short-circuiting methods

Donald Raab

Apr 9, 2018·3 min read

Learn the methods in Eclipse Collections that short-circuit and return a result as soon as a condition is met.

What are the short-circuiting methods?

The short-circuiting methods in Eclipse Collections all take a Predicate or Predicate2 as a parameter. We refer to them as short-circuiting methods because as soon as the condition is met for a particular algorithm, the loop is broken out of and a result is immediately returned.

The short-circuiting methods in Eclipse Collections are:

• detect / detectWith — returns the first object that the predicate matches or null if none match
• detectIfNone / detectWithIfNone — returns the first object that the predicate matches or returns the result of evaluating the Function0
• detectOptional / detectWithOptional — returns an Optional with the first object that the predicate matches or Optional.empty()
• detectIndex / detectLastIndex (Ordered Only) — returns the index of the first or last object that the predicate matches or -1 if none match
• anySatisfy / anySatisfyWith — returns true if the predicate matches any object
• allSatisfy / allSatisfyWith — returns true if the predicate matches all of the objects
• noneSatisfy / noneSatisfyWith — returns true if the predicate doesn’t match any of the objects

The methods that include the suffix “With” all take Predicate2, while the other methods take a Predicate.

All of the examples in this blog are written using the Java 10 Local-Variable Type Inference feature (aka var).

A few forms of detect

@Test
public void detect()
{
    var mutableList = 
        mList("the", "quick", "brown", "fox", "jumps");
    var immutableList = 
        iList("over", "the", "lazy", "dog");

    var the1 =
        mutableList.detect("the"::equals);
    var the2 =
        immutableList.detectIfNone("fox"::equals, () -> "the");

    Assert.assertEquals(the1, the2);

    var the3 =
        mutableList.detectWith(Object::equals, "the");
    var the4 =
        immutableList.detectWithIfNone(Object::equals, "fox", 
            () -> "the");

    Assert.assertEquals(the3, the4);

    var the5 =
        mutableList.detectOptional(s -> s.endsWith("e"));
    var the6 =
        immutableList.detectWithOptional(String::startsWith, "t");

    Assert.assertEquals(the5.get(), the6.get());
}

Detecting the first and last index

@Test
public void detectIndex()
{
    var mutableList = 
        mList("the", "quick", "brown", "fox", "jumps");
    var immutableList = 
        iList("over", "the", "lazy", "dog");

    var the1 = mutableList.detectIndex("the"::equals);
    var the2 = immutableList.detectIndex("the"::equals);
    Assert.assertEquals(0, the1);
    Assert.assertEquals(1, the2);

    var fox = mutableList.detectLastIndex("fox"::equals);
    var dog = immutableList.detectLastIndex("dog"::equals);
    Assert.assertEquals(3, fox);
    Assert.assertEquals(3, dog);
}

Examples of Any/All/NoneSatisfy

@Test
public void anyAllNoneSatisfy()
{
    var list = mList("the", "quick", "brown", "fox");

    Assert.assertTrue(list.anySatisfy(s -> s.endsWith("e")));
    Assert.assertFalse(list.anySatisfyWith(String::endsWith, "z"));    Assert.assertFalse(list.allSatisfyWith(String::endsWith, "e"));
    Assert.assertTrue(list.allSatisfy(s -> !s.isEmpty()));    Assert.assertFalse(list.noneSatisfyWith(String::endsWith, "x"));
    Assert.assertTrue(list.noneSatisfy(String::isEmpty));
}

Try out short-circuiting methods in the EC Katas

Here’s a few solutions demonstrating short-circuiting methods in Exercise #2 of the Eclipse Collections Pet Kata.

Check out this presentation to learn more about the origins, design and evolution of the Eclipse Collections API. There is also a video covering the slides that was recorded at an Eclipse Community Virtual Meet-up.

Eclipse Collections is open for contributions. If you like the library, you can let us know by starring it on GitHub.