Snippets of Java code

AddToListWhileIterating.java

@Test
void standardForLoop() {
    final List<String> fruit = new ArrayList<>(
        Arrays.asList("apple", "banana", "orange", "mango")
    );
    int counter = 0;
    for (int i = 0; i < fruit.size(); i++) {
        if (counter++ < 10) {
            fruit.add("pineapple");
        }
    }
    assertThat(counter).isEqualTo(fruit.size());
    assertThat(fruit).hasSize(14);
}


@Test
void forInLoop() {
    assertThatThrownBy(() -> {
        final List<String> fruit = new ArrayList<>(
            Arrays.asList("apple", "banana", "orange", "mango")
        );
        for (final String item : fruit) {
            fruit.add("pineapple");
        }
    }).isInstanceOf(ConcurrentModificationException.class);
}


@Test
void forEachLoop() {
    assertThatThrownBy(() -> {
        final List<String> fruit = new ArrayList<>(
            Arrays.asList("apple", "banana", "orange", "mango")
        );
        fruit.forEach(item -> fruit.add("pineapple"));
    }).isInstanceOf(ConcurrentModificationException.class);
}

Snippets.java

// STREAMS

// Convert List of numbers as Strings into a Set of Integers.
// This would remove duplicates by nature of how the Set works.
final List<String> numberStrings = Arrays.asList("1", "2", "2", "3", "4", "4");
final Set<Integer> uniqueNumbers = numberStrings.stream().map(Integer::parseInt).collect(Collectors.toSet());

// STRING FORMATTING
void example1() {
    // https://docs.oracle.com/javase/7/docs/technotes/guides/language/underscores-literals.html
    final int MILES_BETWEEN_EARTH_AND_MOON = 226_000;
    final int MILLISECONDS_PER_HOUR = 3_600_000;

    // https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/Formatter.html
    String.format(
        "There are %s miles between the earth and moon at perigee.",
        MILES_BETWEEN_EARTH_AND_MOON
    );
    // There are 226000 miles between the earth and moon at perigee.
    
    String.format(
        "There are %s milliseconds in one hour.",
        MILLISECONDS_PER_HOUR
    );
    // There are 3600000 milliseconds in one hour.
    
    String.format(
        "There are %,d miles between the earth and moon at perigee.",
        MILES_BETWEEN_EARTH_AND_MOON
    );
    // There are 226,000 miles between the earth and moon at perigee.
    
    String.format(
        "There are %,d milliseconds in one hour.",
        MILLISECONDS_PER_HOUR
    );
    // There are 3,600,000 milliseconds in one hour.
}