RFR (JDK11) 8137326: Methods for comparing CharSequence, StringBuilder, and StringBuffer

Tagir Valeev amaembo at gmail.com
Tue Jan 30 04:07:40 UTC 2018


An AbstractStringBuilder#compareTo implementation is wrong. You cannot
simply compare the whole byte array. Here's the test-case:

public class Test {
  public static void main(String[] args) {
    StringBuilder sb1 = new StringBuilder("test1");
    StringBuilder sb2 = new StringBuilder("test2");

We truncated the stringbuilders making their content equal, so
sb1.toString().compareTo(sb2.toString()) is 0, but compareTo compares
the original content (before the truncation) as truncation, of course,
does not zero the truncated bytes, neither does it reallocate the
array (unless explicitly asked via trimToSize).

With best regards,
Tagir Valeev.

On Fri, Jan 26, 2018 at 10:00 AM, Joe Wang <huizhe.wang at oracle.com> wrote:
> Hi,
> Adding methods for comparing CharSequence, StringBuilder, and StringBuffer.
> The Comparable implementations for StringBuilder/Buffer are similar to that
> of String, allowing comparison operations between two
> StringBuilders/Buffers, e.g. aStringBuilder.compareTo(anotherStringBuilder).
> For CharSequence however, refer to the comments in JIRA, a static method
> 'compare' is added instead of implementing the Comparable interface. This
> 'compare' method may take CharSequence implementations such as String,
> StringBuilder and StringBuffer, making it possible to perform comparison
> among them. The previous example for example is equivalent to
> CharSequence.compare(aStringBuilder, anotherStringBuilder).
> Tests for java.base have been independent from each other. The new tests are
> therefore created to have no dependency on each other or sharing any code.
> JBS: https://bugs.openjdk.java.net/browse/JDK-8137326
> webrev: http://cr.openjdk.java.net/~joehw/jdk11/8137326/webrev/
> Thanks,
> Joe

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