Java 比较问题 - 比较方法违反了其通用约定 [重复]

问：

我正在尝试对一些数字进行排序。我收到一个“java.lang.IllegalArgumentException：比较方法违反了其一般约定！执行以下代码时异常。

import org.apache.commons.lang3.StringUtils;

public class ComparatorTest {

    public static void main(String[] args) {
        List<String> ll = List.of("1.A", "1.A.1", "10.A", "10.A.1", "10.A.2", "10.A.3", "12.A", "12.A.1", "12.A.2",
                "12.A.4", "12.A.6", "1A.2", "2.A.1", "2.A.1.b", "2.A.1.b.1", "2.A.1.b.2", "2.A.1.b.3", "20.A.1",
                "20.A.1.a", "20.A.1.b", "20.A.1.b.1", "20.A.1.b.2", "3.A.1", "3.A.1.a", "3.A.1.a.1", "3.A.1.a.2",
                "3.A.1.a.3", "3.A.1.a.4", "3.A.1.b", "3.A.10", "6.A.1", "9.A.1");
        
        ArrayList<String> l2 = new ArrayList<>(ll);
        Collections.sort(l2, (obj1, obj2) -> {
            try {
                String[] prodClass1 = obj1.split("\\.");
                String[] prodClass2 = obj2.split("\\.");
                for (int i = 0; (i < prodClass1.length) && (i < prodClass2.length); i++) {
                    if (!prodClass1[i].equals(prodClass2[i])) {
                        if (StringUtils.isNumeric(prodClass1[i]) && StringUtils.isNumeric(prodClass2[i])) {
                            return Integer.valueOf(prodClass1[i]).compareTo(Integer.valueOf(prodClass2[i]));
                        } else {
                            return prodClass1[i].compareToIgnoreCase(prodClass2[i]);
                        }
                    }
                }
                return obj1.compareToIgnoreCase(obj2);
            } catch (Exception e) {
                e.printStackTrace();
                return obj1.compareToIgnoreCase(obj2);
            }
        });
        System.out.println(l2);
    }
    
}

如果我从列表 ll 中删除任何 1 个元素，代码就可以正常工作。

我认为这必须做一些与equals（）和compare（）方法有关的事情。但是有人能指出这里的问题吗？

如果我在自定义比较器中添加一个额外的条件，它就可以工作。为什么会这样？任何人都可以查明问题所在。

修改后的代码

Collections.sort(l2, (obj1, obj2) -> {
            try {
                String[] prodClass1 = obj1.split("\\.");
                String[] prodClass2 = obj2.split("\\.");
                for (int i = 0; (i < prodClass1.length) && (i < prodClass2.length); i++) {
                    if (!prodClass1[i].equals(prodClass2[i])) {
                        if (StringUtils.isNumeric(prodClass1[i]) && StringUtils.isNumeric(prodClass2[i])) {
                            return Integer.valueOf(prodClass1[i]).compareTo(Integer.valueOf(prodClass2[i]));
                        } else if (StringUtils.isNumeric(prodClass1[i]) || StringUtils.isNumeric(prodClass2[i])) {
                            return StringUtils.isNumeric(prodClass1[i]) ? -1 : 1;
                        } else {
                            return prodClass1[i].compareToIgnoreCase(prodClass2[i]);
                        }
                    }
                }
                return obj1.compareToIgnoreCase(obj2);
            } catch (Exception e) {
                e.printStackTrace();
                return obj1.compareToIgnoreCase(obj2);
            }
        });

以下是我在添加一些日志后执行代码时的输出：

prodClass1: [3, A, 1, a, 1] Comparing with prodClass2: [2, A, 1, b, 3]
prodClass1: [2, A, 1, b, 3] Comparing with prodClass2: [3, A, 1, a]
prodClass1: [2, A, 1, b, 3] Comparing with prodClass2: [3, A, 1]
Exception in thread "main" java.lang.IllegalArgumentException: Comparison method violates its general contract!
    at java.base/java.util.TimSort.mergeHi(TimSort.java:903)
    at java.base/java.util.TimSort.mergeAt(TimSort.java:520)
    at java.base/java.util.TimSort.mergeForceCollapse(TimSort.java:461)
    at java.base/java.util.TimSort.sort(TimSort.java:254)
    at java.base/java.util.Arrays.sort(Arrays.java:1515)
    at java.base/java.util.ArrayList.sort(ArrayList.java:1750)
    at java.base/java.util.Collections.sort(Collections.java:179)
    at core.ComparatorTest.main(ComparatorTest.java:30)