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  1. DZone
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  4. Java 11 String API Updates

Java 11 String API Updates

The imminent JDK 11 is bringing with it some new features to the String API! Let's take a dive and see what some of those features are and how they work.

Grzegorz Piwowarek user avatar by
Grzegorz Piwowarek
·
Sep. 20, 18 · News
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It turns out that the new upcoming LTS JDK 11 release is bringing a few interesting String API updates to the table.

Let's have a look at them and the interesting facts surrounding them.

String#repeat

One of the coolest additions to the String API is the repeat() method. This method allows concatenating a String with itself a given number of times:

var string = "foo bar ";

var result = string.repeat(2); // foo bar foo bar


But, I was most excited about trying out the corner cases — if you try to repeat a String  0 times, you will always get an empty String :

@Test
void shouldRepeatZeroTimes() {
    var string = "foo";

    var result = string.repeat(0);

    assertThat(result).isEqualTo("");
}


The same applies to repeating an empty String:

@Test
void shouldRepeatEmpty() {
    var string = "";

    var result = string.repeat(Integer.MAX_VALUE);

    assertThat(result).isEqualTo("");
}


It might be tempting to think that it's just relying on a StringBuilder underneath, but that's not the case. The actual implementation is much more resource-effective:

public String repeat(int count) {
    if (count < 0) {
        throw new IllegalArgumentException("count is negative: " + count);
    }
    if (count == 1) {
        return this;
    }
    final int len = value.length;
    if (len == 0 || count == 0) {
        return "";
    }
    if (len == 1) {
        final byte[] single = new byte[count];
        Arrays.fill(single, value[0]);
        return new String(single, coder);
    }
    if (Integer.MAX_VALUE / count < len) {
        throw new OutOfMemoryError("Repeating " + len + " bytes String " + count +
                " times will produce a String exceeding maximum size.");
    }
    final int limit = len * count;
    final byte[] multiple = new byte[limit];
    System.arraycopy(value, 0, multiple, 0, len);
    int copied = len;
    for (; copied < limit - copied; copied <<= 1) {
        System.arraycopy(multiple, 0, multiple, copied, copied);
    }
    System.arraycopy(multiple, 0, multiple, copied, limit - copied);
    return new String(multiple, coder);
}


From the Compressed Strings point of view, the following fragment might look suspicious at first sight (non-latin single-character String occupies two bytes), but it's important to remember that value.length is the size of the internal byte array and not the String itself:

final int len = value.length;
// ...
if (len == 1) {
    final byte[] single = new byte[count];
    Arrays.fill(single, value[0]);
    return new String(single, coder);
}


String#isBlank

That one is super straightforward. Now, we can check if a String instance is empty or contains whitespace (defined by Character#isWhitespace(int)) exclusively:

var result = " ".isBlank(); // true


String#strip

We can easily get rid of all the whitespace from each String now:

assertThat(" ".strip()).isEmpty();


This one will come in handy to avoid excessive whitespace once Raw Strings arrive in Java.

Additionally, we can narrow the operation only to trailing/leading whitespace:

assertThat("  foo  ".stripLeading()).isEqualTo("foo  ");

assertThat("  foo  ".stripTrailing()).isEqualTo("  foo");


However, you might be asking yourself how does this one differ from String#trim?

It turns out that String#strip is a modern Unicode-aware alternative that relies on the same definition of whitespace as  String#isBlank.

More details about it can be found straight at the source.

String#lines

Using this new method, we can easily split a String instance into a Stream<String> of separate lines:

"foo\nbar".lines().forEach(System.out::println);

// foo
// bar


What's really cool is that, instead of splitting a String and converting it into a Stream, specialized Spliterators were implemented (one for Latin and one for UTF-16 Strings) that makes it possible to stay lazy:

private final static class LinesSpliterator implements Spliterator<String> {
    private byte[] value;
    private int index;        // current index, modified on advance/split
    private final int fence;  // one past last index

    LinesSpliterator(byte[] value) {
        this(value, 0, value.length);
    }

    LinesSpliterator(byte[] value, int start, int length) {
        this.value = value;
        this.index = start;
        this.fence = start + length;
    }

    private int indexOfLineSeparator(int start) {
        for (int current = start; current < fence; current++) {
            byte ch = value[current];
            if (ch == '\n' || ch == '\r') {
                return current;
            }
        }
        return fence;
    }

    private int skipLineSeparator(int start) {
        if (start < fence) {
            if (value[start] == '\r') {
                int next = start + 1;
                if (next < fence && value[next] == '\n') {
                    return next + 1;
                }
            }
            return start + 1;
        }
        return fence;
    }

    private String next() {
        int start = index;
        int end = indexOfLineSeparator(start);
        index = skipLineSeparator(end);
        return newString(value, start, end - start);
    }

    @Override
    public boolean tryAdvance(Consumer<? super String> action) {
        if (action == null) {
            throw new NullPointerException("tryAdvance action missing");
        }
        if (index != fence) {
            action.accept(next());
            return true;
        }
        return false;
    }

    @Override
    public void forEachRemaining(Consumer<? super String> action) {
        if (action == null) {
            throw new NullPointerException("forEachRemaining action missing");
        }
        while (index != fence) {
            action.accept(next());
        }
    }

    @Override
    public Spliterator<String> trySplit() {
        int half = (fence + index) >>> 1;
        int mid = skipLineSeparator(indexOfLineSeparator(half));
        if (mid < fence) {
            int start = index;
            index = mid;
            return new LinesSpliterator(value, start, mid - start);
        }
        return null;
    }

    @Override
    public long estimateSize() {
        return fence - index + 1;
    }

    @Override
    public int characteristics() {
        return Spliterator.ORDERED | Spliterator.IMMUTABLE | Spliterator.NONNULL;
    }
}


Sources

Code snippets from this article can be found on GitHub.

API Strings Data Types Java (programming language)

Published at DZone with permission of Grzegorz Piwowarek, DZone MVB. See the original article here.

Opinions expressed by DZone contributors are their own.

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