Explore Java 12: String Indent, Transform, File Mismatch, Teeing Collector

String Enhancements

Java 12 adds two new methods for string handling.

String Indent

Method String indent(int n) adjusts indentation based on the integer n. If n>0, n spaces are added at the start of each line; if n<0, up to |n| spaces are removed from each line, possibly deleting all leading spaces without adding new lines.

String text = " Hello 
 Java12";
System.out.println("Before indent");
System.out.println(text);
System.out.println("Indent by 2");
String indent2 = text.indent(2);
System.out.println(indent2);
System.out.println("Indent by -3");
String indent3 = text.indent(-3);
System.out.println(indent3);

String Transform

Method String transform(Function<? super String, ? extends R> f) allows functional transformation of a string.

String txt = "hello ";
String s = txt.transform(str -> str.repeat(2));

Java’s each version strengthens functional programming.

File Content Mismatch

Files.mismatch(Path, Path)

returns the position of the first differing byte between two files, or -1L if they are identical.

// file comparison
Path p1 = Files.createTempFile("file1", "txt");
Path p2 = Files.createTempFile("file2", "txt");
Files.writeString(p1, "felord.cn");
Files.writeString(p2, "felord.cn");
long mismatch = Files.mismatch(p1, p2); // -1L indicates same content

Collectors::teeing

The new teeing collector enables simultaneous collection of multiple results from a stream, such as computing average and sum then dividing them.

Double meanPercentage = Stream.of(1,2,3,4,5)
    .collect(Collectors.teeing(
        Collectors.averagingDouble(i -> i),
        Collectors.summingDouble(i -> i),
        (average, total) -> average / total));

Compact Number Formatting

CompactNumberFormat

provides locale‑aware compact representation of large numbers.

NumberFormat cnFormat = NumberFormat.getCompactNumberInstance(Locale.CHINA, NumberFormat.Style.SHORT);
cnFormat.setMaximumFractionDigits(3);
String cformat = cnFormat.format(82323); // 8.232万

NumberFormat usFormat = NumberFormat.getCompactNumberInstance(Locale.US, NumberFormat.Style.SHORT);
usFormat.setMaximumFractionDigits(3);
String uformat = usFormat.format(82323); // 82.323K

Other Notes

Java 12 also includes preview features and JVM enhancements, but no major highlights beyond those mentioned.