Java 7：java.lang.IllegalArgumentException：比较方法违反了其一般合同

Question

I am in the process of upgrading our project to java 7. I ran into the Illegal Argument exception for Collections.sort(). I know the cause of the exception is the new Timsort in java 7 (I did go throw though all the questions raised previously on this issue). Now I need to modify the compare logic to overcome the exception. Here is my compare method

if (o1.isLookup() && !o2.isLookup()) {
    return -1;
}
if (!o1.isLookup() && o2.isLookup()) {
    return 1;
}

if (o1.dependsOn(o2)) {
    return 1;
}
if (o2.dependsOn(o1)) {
    return -1;
}
return 0;

1. I tried overriding the equals() method , with the same logic as compare, thinking if equals and compare return the same result it should resolve the issue; but it didn't work as expected .

2. When I split the compare method into two with separate comparators as shown below then the sort(using both comparators) does not throw any exception. What could be the possible reason?

Code Below:

protected Comparator<EntityWrapper> getComparator2() {      
    return new Comparator<EntityWrapper>() {
        public int compare(EntityWrapper o1, EntityWrapper o2) {
            if (o1.dependsOn(o2.entityClass)) {
                // This depends on otherWrapper
                return 1;
            }
            if (o2.dependsOn(o1.entityClass)) {
                // OtherWrapper depends on this
                return -1;
            }
            return 0;
        }
    };
}

protected Comparator<EntityWrapper> getComparator1() {
    return new Comparator<EntityWrapper>() {
public int compare(EntityWrapper o1, EntityWrapper o2) {
        if (o1.isLookup() && !o2.isLookup()) {
            return -1;
        }
        if (!o1.isLookup() && o2.isLookup()) {
            return 1;
        }
        return 0;
    };
}

Answer 1

It also has something to do with the version of JDK. The implementation method in JDK 7 has been changed for which you are violating one of the 3 rules of compareTo method contract.

Look at this:

Description: The sorting algorithm used by java.util.Arrays.sort and (indirectly) by java.util.Collections.sort has been replaced. The new sort implementation may throw an IllegalArgumentException if it detects a Comparable that violates the Comparable contract. The previous implementation silently ignored such a situation. If the previous behaviour is desired, you can use the new system property, java.util.Arrays.useLegacyMergeSort, to restore previous mergesort behaviour.

System.setProperty("java.util.Arrays.useLegacyMergeSort", "true");

Answer 2

Aren't you missing ".entityClass" such as:

if (o1.isLookup() && !o2.isLookup()) {
    return -1;
}
if (!o1.isLookup() && o2.isLookup()) {
    return 1;
}

if (o1.dependsOn(o2.entityClass)) {
    return 1;
}
if (o2.dependsOn(o1.entityClass)) {
    return -1;
}
return 0;