英文:
Comparing two generics in compareTo()
问题
我有以下的类签名：
public class SkipListSet<T extends Comparable<T>> implements SortedSet<T>
还有一个在SkipListSet类之外的类：
class Node<T extends Comparable<T>>
第二个类充当一个包装类，包含以下内容：
T data;
List<Node<T>> tower;
Node<T> nextNode = null;
Node<T> prevNode = null;
当我尝试在我的Node类中实现compareTo()方法时：
public int compareTo(T somePayLoad) {
if (this.data < somePayLoad)
return -1;
else if (this.data > somePayLoad)
return 1;
else
return 0;
}
我得到以下错误：
SkipListSet.java:171: error: bad operand types for binary operator '<'
if (this.data < somePayLoad)
^
first type: T
second type: T
where T is a type-variable:
T extends Comparable<T> declared in class SkipListSet.Node
为什么我不能在compareTo方法中比较两个T类型的数据？
英文:
I have the following class signatures:
public class SkipListSet<T extends Comparable<T>> implements SortedSet<T>
and another class outside of SkipListSet class:
class Node<T extends Comparable<T>>
The second one acts as a wrapper class that contains the following:
T data;
List<Node<T>> tower;
Node<T> nextNode = null;
Node<T> prevNode = null;
When I try implementing compareTo() method in my Node class:
public int compareTo(T somePayLoad) {
if (this.data < somePayLoad)
return -1;
else if (this.data > somePayLoad)
return 1;
else
return 0;
}
I get the following error:
SkipListSet.java:171: error: bad operand types for binary operator '<'
if (this.data < somePayLoad)
^
first type: T
second type: T
where T is a type-variable:
T extends Comparable<T> declared in class SkipListSet.Node
Why is it that I can't compare two types of T data in my compareTo method?
答案1
得分: 2
你不能在对象上使用 '<' 或 '>'。我认为你需要的是：
public int compareTo(T somePayLoad) {
return this.data.compareTo(somePayLoad.data);
}
（添加空值检查）。
英文:
You can't use '<' or '>' on objects. I think what you need is:
public int compareTo(T somePayLoad) {
return this.data.compareTo(somePayLoad.data);
}
(Add null checks).
答案2
得分: 0
不需要编写compareTo方法。
T类应该实现Comparable接口。
TestSkipListSet<NodeData> list = new TestSkipListSet<NodeData>();
TestSkipListSet<NodeData2> list2 = new TestSkipListSet<NodeData2>();
class NodeData implements Comparable<NodeData> {
int value;
@Override
public int compareTo(@NonNull NodeData o) {
return this.value - o.value;
}
}
class NodeData2 implements Comparable<NodeData2> {
TestUser value;
@Override
public int compareTo(@NonNull NodeData2 o) {
return this.value.age - o.value.age;
}
class TestUser {
int age;
}
}
public class TestSkipListSet<T extends Comparable<T>> implements SortedSet<T> {
...
}
英文:
You don't need to write the compareTo method.
T class should implement Comparable inteface.
TestSkipListSet<NodeData> list = new TestSkipListSet<NodeData>();
TestSkipListSet<NodeData2> list2 = new TestSkipListSet<NodeData2>();
class NodeData implements Comparable<NodeData> {
int value;
@Override
public int compareTo(@NonNull NodeData o) {
return this.value - o.value;
}
}
class NodeData2 implements Comparable<NodeData2> {
TestUser value;
@Override
public int compareTo(@NonNull NodeData2 o) {
return this.value.age-o.value.age;
}
}
class TestUser{
int age;
}
public class TestSkipListSet<T extends Comparable<T>> implements SortedSet<T>{
...
}
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