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

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

Hello!

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"); sb1.setLength(4); sb2.setLength(4); System.out.println(sb1.compareTo(sb2)); System.out.println(sb1.toString().compareTo(sb2.toString())); } }

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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