String split()方法在jdk7和jdk8下面不一樣結果

import java.util.Arrays;
import java.util.regex.Pattern;

public class StringSplit {
    public static void main(String[] args) {
        String str = "ABC";

        // 測試String#split()方法
        String[] elems = str.split("");
        System.out.println(Arrays.toString(elems));

        // 結果：
        //   Java 7 -> [, A, B, C]
        //   Java 8 -> [A, B, C]

        // 測試Pattern#split()方法
        Pattern delimiter = Pattern.compile("");
        elems = delimiter.split(str);
        System.out.println(Arrays.toString(elems));
    }
}

查了一下，發現java.util.regex.Pattern#String[] split(CharSequence input, int limit)方法中，增長了下面的處理。

// Add segments before each match found
        while(m.find()) {
            if (!matchLimited || matchList.size() < limit - 1) {
                if (index == 0 && index == m.start() && m.start() == m.end()) {
                    // no empty leading substring included for zero-width match
                    // at the beginning of the input char sequence.
                    continue;
                }
                String match = input.subSequence(index, m.start()).toString();
                matchList.add(match);
                index = m.end();
            } else if (matchList.size() == limit - 1) { // last one
                String match = input.subSequence(index,
                                                 input.length()).toString();
                matchList.add(match);
                index = m.end();
            }
        }