Java8の関数インターフェイスのdefaultメソッド.java

    @Test
    public void Functionのdefaultメソッド() throws Exception {
        Function<String, String> s1 = s -> s + "1";
        Function<String, String> s2 = s -> s + "2";
        Function<String, String> s3 = s -> s + "3";

        // andThen
        String res1 = s1.andThen(s2).andThen(s3).apply("start:");
        assertThat(res1, is("start:123"));

        // compose
        String res2 = s1.compose(s2).compose(s3).apply("start:");
        assertThat(res2, is("start:321"));

        // identity
        Function<String, String> f1 = Function.identity();
        Function<String, String> f2 = s -> s;
        String actual = f1.apply("test");
        String expected = f2.apply("test");

        assertThat(actual, is(expected));
    }

    @Test
    public void Consumerのdefaultメソッド() throws Exception {
        Consumer<String> s1 = System.out::print;
        Consumer<String> s2 = System.out::print;

        // result: xx
        s1.andThen(s2).accept("x");
    }

    @Test
    public void Predicateのdefaultメソッド() throws Exception {
        Predicate<String> p1 = s -> s.length() > 1;
        Predicate<String> p2 = s -> s.length() < 10;

        new ArrayList<String>().stream()
                .filter(p1.and(p2))      // 1 < param && param < 10
                .filter(p1.or(p2))       // 1 < param || param < 10
                .filter(p1.negate())     // !(1 < param)
                .filter(isEqual("test")) // "test".equals(param)
                .filter(isEqual(null))   // param == null
                .collect(toList());
    }