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copied!<p>If in doubt, measure it. My results showed no significant difference. When run, the following program produced:</p> <pre><code>7421714 (abstract) 5840702 (interface) 7621523 (abstract) 5929049 (interface) </code></pre> <p>But when I switched the places of the two loops:</p> <pre><code>7887080 (interface) 5573605 (abstract) 7986213 (interface) 5609046 (abstract) </code></pre> <p>It appears that abstract classes are slightly (~6%) faster, but that should not be noticeable; These are nanoseconds. 7887080 nanoseconds are ~7 milliseconds. That makes it a difference of 0.1 millis per 40k invocations (Java version: 1.6.20)</p> <p>Here's the code:</p> <pre><code>public class ClassTest { public static void main(String[] args) { Random random = new Random(); List<Foo> foos = new ArrayList<Foo>(40000); List<Bar> bars = new ArrayList<Bar>(40000); for (int i = 0; i < 40000; i++) { foos.add(random.nextBoolean() ? new Foo1Impl() : new Foo2Impl()); bars.add(random.nextBoolean() ? new Bar1Impl() : new Bar2Impl()); } long start = System.nanoTime(); for (Foo foo : foos) { foo.foo(); } System.out.println(System.nanoTime() - start); start = System.nanoTime(); for (Bar bar : bars) { bar.bar(); } System.out.println(System.nanoTime() - start); } abstract static class Foo { public abstract int foo(); } static interface Bar { int bar(); } static class Foo1Impl extends Foo { @Override public int foo() { int i = 10; i++; return i; } } static class Foo2Impl extends Foo { @Override public int foo() { int i = 10; i++; return i; } } static class Bar1Impl implements Bar { @Override public int bar() { int i = 10; i++; return i; } } static class Bar2Impl implements Bar { @Override public int bar() { int i = 10; i++; return i; } } } </code></pre>

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