Tuesday, 12 July 2016

[Java 8 / Functional programming] Functional util that invokes a command n times.

Recently I've been doing major refactoring of integration tests. I've found many tests which do stuff like that:
for (int i = 0; i < 256; i++) {
It's pretty ugly, isn't it ? It would be nice to have a small tool that invokes given piece of code n times. In Java 8 we can use IntStream:
IntStream.range(0, 256).forEach(i -> addProduct(UUID.randomUUID().toString()));
Looks better but it's still not very readable. Again I've started with a test that specifies how the tool should work:
    public void shouldInvokeCommandFiveTimes() throws Exception {
        // given
        final List<String> list = newArrayList();

        // when
        times(5).invoke(() -> list.add("item"));

        // then
        assertThat(list).containsExactly("item", "item", "item", "item", "item");
I've come up with the following class:
 * @author Grzegorz Taramina
 *         Created on: 12/07/16
public class Times {
    private final int times;

    private Times(final int times) {
        this.times = times;

    public static Times times(final int times) {
        Assert.isTrue(times >= 0, "times must be at least equal to zero");
        return new Times(times);

    public void invoke(final Runnable runnable) {
        IntStream.range(0, times).forEach(i -> runnable.run());
It's very simple but makes code concise and readable:
times(5).invoke(() -> addProduct(randomUUID().toString));
I might have exaggerated saying that this is functional tool. It's simply higher order function but very useful.

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