我正在尝试在 Groovy 中开发一个项目，我发现我的一些测试以一种奇怪的方式失败：我有一个界面Version extends Comparable<Version>有两个具体的子类。两者都覆盖equals(Object) and compareTo(Version)- 但是，如果我尝试比较两个实例Version具有不同的具体类型，使用==，即使显式的相等性检查也会失败equals and compareTo检查通过。
如果我删除extends Comparable<Version>部分Version，我得到了预期的行为 -==给出相同的结果equals would.
我在其他地方读到 Groovy 委托== to equals()除非该类实现Comparable，在这种情况下它委托给compareTo。但是，我发现两者都声明了两个实例的情况Version是平等的，但==检查失败。
我创建了一个 SSCCE 来演示这种行为here https://groovyconsole.appspot.com/script/5705097937944576.
下面还提供了完整的代码：
// Interface extending Comparable
interface Super extends Comparable<Super> {
int getValue()
}
class SubA implements Super {
int getValue() { 1 }
int compareTo(Super that) { this.value <=> that.value }
boolean equals(Object o) {
if (o == null) return false
if (!(o instanceof Super)) return false
this.value == o.value
}
}
class SubB implements Super {
int getValue() { 1 }
int compareTo(Super that) { this.value <=> that.value }
boolean equals(Object o) {
if (o == null) return false
if (!(o instanceof Super)) return false
this.value == o.value
}
}
// Interface not extending Comparable
interface AnotherSuper {
int getValue()
}
class AnotherSubA implements AnotherSuper {
int getValue() { 1 }
boolean equals(Object o) {
if (o == null) return false
if (!(o instanceof AnotherSuper)) return false
this.value == o.value
}
}
class AnotherSubB implements AnotherSuper {
int getValue() { 1 }
boolean equals(Object o) {
if (o == null) return false
if (!(o instanceof AnotherSuper)) return false
this.value == o.value
}
}
// Check with comparable versions
def a = new SubA()
def b = new SubB()
println "Comparable versions equality check: ${a == b}"
println "Explicit comparable equals check: ${a.equals(b)}"
println "Explicit comparable compareTo check: ${a.compareTo(b)}"
// Check with non-comparable versions
def anotherA = new AnotherSubA()
def anotherB = new AnotherSubB()
println "Non-comparable versions equality check: ${anotherA == anotherB}"
println "Explicit non-comparable equals check: ${anotherA.equals(anotherB)}"
我要返回的是：
Comparable versions equality check: false
Explicit comparable equals check: true
Explicit comparable compareTo check: 0
Non-comparable versions equality check: true
Explicit non-comparable equals check: true
EDIT
我想我明白为什么现在会发生这种情况，感谢JIRA讨论 https://jira.codehaus.org/browse/GROOVY-3364Poundex 链接到下面。
来自格罗维默认类型转换类 https://github.com/groovy/groovy-core/blob/master/src/main/org/codehaus/groovy/runtime/typehandling/DefaultTypeTransformation.java#L557，用于处理相等/比较检查，我假设compareEqual当以下形式的语句时首先调用方法x == y正在评估：
public static boolean compareEqual(Object left, Object right) {
if (left == right) return true;
if (left == null || right == null) return false;
if (left instanceof Comparable) {
return compareToWithEqualityCheck(left, right, true) == 0;
}
// handle arrays on both sides as special case for efficiency
Class leftClass = left.getClass();
Class rightClass = right.getClass();
if (leftClass.isArray() && rightClass.isArray()) {
return compareArrayEqual(left, right);
}
if (leftClass.isArray() && leftClass.getComponentType().isPrimitive()) {
left = primitiveArrayToList(left);
}
if (rightClass.isArray() && rightClass.getComponentType().isPrimitive()) {
right = primitiveArrayToList(right);
}
if (left instanceof Object[] && right instanceof List) {
return DefaultGroovyMethods.equals((Object[]) left, (List) right);
}
if (left instanceof List && right instanceof Object[]) {
return DefaultGroovyMethods.equals((List) left, (Object[]) right);
}
if (left instanceof List && right instanceof List) {
return DefaultGroovyMethods.equals((List) left, (List) right);
}
if (left instanceof Map.Entry && right instanceof Map.Entry) {
Object k1 = ((Map.Entry)left).getKey();
Object k2 = ((Map.Entry)right).getKey();
if (k1 == k2 || (k1 != null && k1.equals(k2))) {
Object v1 = ((Map.Entry)left).getValue();
Object v2 = ((Map.Entry)right).getValue();
if (v1 == v2 || (v1 != null && DefaultTypeTransformation.compareEqual(v1, v2)))
return true;
}
return false;
}
return ((Boolean) InvokerHelper.invokeMethod(left, "equals", right)).booleanValue();
}
请注意，如果表达式的 LHS 是一个实例Comparable，正如我提供的示例中一样，比较被委托给compareToWithEqualityCheck:
private static int compareToWithEqualityCheck(Object left, Object right, boolean equalityCheckOnly) {
if (left == right) {
return 0;
}
if (left == null) {
return -1;
}
else if (right == null) {
return 1;
}
if (left instanceof Comparable) {
if (left instanceof Number) {
if (right instanceof Character || right instanceof Number) {
return DefaultGroovyMethods.compareTo((Number) left, castToNumber(right));
}
if (isValidCharacterString(right)) {
return DefaultGroovyMethods.compareTo((Number) left, ShortTypeHandling.castToChar(right));
}
}
else if (left instanceof Character) {
if (isValidCharacterString(right)) {
return DefaultGroovyMethods.compareTo((Character)left, ShortTypeHandling.castToChar(right));
}
if (right instanceof Number) {
return DefaultGroovyMethods.compareTo((Character)left,(Number)right);
}
}
else if (right instanceof Number) {
if (isValidCharacterString(left)) {
return DefaultGroovyMethods.compareTo(ShortTypeHandling.castToChar(left),(Number) right);
}
}
else if (left instanceof String && right instanceof Character) {
return ((String) left).compareTo(right.toString());
}
else if (left instanceof String && right instanceof GString) {
return ((String) left).compareTo(right.toString());
}
if (!equalityCheckOnly || left.getClass().isAssignableFrom(right.getClass())
|| (right.getClass() != Object.class && right.getClass().isAssignableFrom(left.getClass())) //GROOVY-4046
|| (left instanceof GString && right instanceof String)) {
Comparable comparable = (Comparable) left;
return comparable.compareTo(right);
}
}
if (equalityCheckOnly) {
return -1; // anything other than 0
}
throw new GroovyRuntimeException(
MessageFormat.format("Cannot compare {0} with value ''{1}'' and {2} with value ''{3}''",
left.getClass().getName(),
left,
right.getClass().getName(),
right));
}
在底部附近，该方法有一个块将比较委托给compareTo方法，但前提是满足某些条件。在我提供的示例中，这些条件都不满足，包括isAssignableFrom检查，因为我提供的示例类（以及我的项目中给我带来问题的代码）是siblings，因此不可相互分配。
我想我明白为什么检查现在失败了，但我仍然对以下事情感到困惑：
- 我该如何解决这个问题？
- 这背后的理由是什么？这是一个错误还是一个设计功能？是否有任何理由为什么一个公共超类的两个子类不应该相互比较？
