Question

编译器说“找不到符号：方法compareTo（java.lang.Object）”。你能告诉我这里的错误在哪里吗？

以下是代码的一部分：

public class OBTComparable<ObjectType> implements Comparable<OBTComparable>
{
    public OTBComparable leftNode = null;
    public OBTComparable mainNode = null;
    public OBTComparable rightNode = null;
    public ObjectType object = null;

    public OBTComparable(ObjectType requiredObject)
    {
        object = requiredObject;
    }

    @Override
    public int compareTo(OBTComparable other)
    {
        if(object.compareTo(other.object) == 0)
            return 0;
        else 
            if (object.compareTo(other.object) > 0)
                return 1;
            else return -1;
    }
}

Answer 1

您需要将ObjectType范围限定为Comparable，因为OBTComparable为delegating compareTo()至ObjectType：

如果您将<ObjectType>更改为<ObjectType extends Comparable<ObjectType>>，则会编译：

public class OBTComparable<ObjectType extends Comparable<ObjectType>> implements Comparable<OBTComparable>

Answer 2

我认为这是您正在寻找的正确代码（为了清晰起见，我将ObjectType替换为T）：

class OBTComparable<T extends Comparable<? super T>> implements Comparable<OBTComparable<T>> {
    public OBTComparable<T> leftNode = null;
    public OBTComparable<T> mainNode = null;
    public OBTComparable<T> rightNode = null;
    public T object = null;

    public OBTComparable(T requiredObject) {
        object = requiredObject;
    }

    @Override
    public int compareTo(OBTComparable<T> other) {
        if (object.compareTo(other.object) == 0) {
            return 0;
        } else if (object.compareTo(other.object) > 0) {
            return 1;
        } else return -1;
    }
}

我在这里做了什么改变：

OBTC Comparable使用类型参数，因此您应该在实现Comparable时显示它。因此，您只需implements Comparable<OBTComparable<T>>而非implements Comparable<OBTComparable>。
您在compareTo方法中比较了两个对象，但它们是否具有可比性？为确保满足此要求，您应该编写OBTComparable<T extends Comparable<T>>而不是OBTComparable<T>。然后您就会知道可以致电compareTo。

Answer 3

ObjectType还必须实现Comparable<ObjectType>。

如果你这样做，我相信这一点：

public int compareTo(OBTComparable other)
{
    if(object.compareTo(other.object) == 0)
        return 0;
    else 
        if (object.compareTo(other.object) > 0)
            return 1;
        else return -1;
}

可以简化为：

public int compareTo(OBTComparable other)
{
    return object.compareTo(other.object);
}

有没有办法实现比较任何提供的参数的compareTo方法？

3 个答案: