java 如何在 TreeSet 中使用自定义类？
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How can I use a custom class in a TreeSet?
提问by SNpn
If I was using a Setsimilar to this:
如果我使用的是Set类似的：
Set<node> s=new TreeSet<node>();
class node {
private int x;
private int y;
}
Would this be acceptable, and since it's a TreeSet, would it also sort it?
这是可以接受的吗，因为它是一个 TreeSet，它也会对它进行排序吗？
回答by Jon Skeet
It's not going to be able to sort it without you implementing Comparable<Node>, and it won't really be an appropriate for set operations until you override equals()and hashCode(). (You don't haveto override equalsand hashCodefor TreeSetto work, but it would make sense to do so.)
如果不实现Comparable<Node>，它将无法对其进行排序，并且在您覆盖equals()和之前，它真的不适合设置操作hashCode()。（你不会有重写equals，并hashCode为TreeSet工作，但它会是有意义的这样做。）
Something like this:
像这样的东西：
final class Node implements Comparable<Node> {
private final int x;
private final int y;
Node(int x, int y) {
this.x = x;
this.y = y;
}
@Override public boolean equals(Object other) {
if (!(other instanceof Node)) {
return false;
}
Node otherNode = (Node) other;
return x == otherNode.x && y == otherNode.y;
}
@Override public int hashCode() {
return x * 31 + y * 17; // For example...
}
@Override public int compareTo(Node other) {
// As of Java 7, this can be replaced with
// return x != other.x ? Integer.compare(x, other.x)
// : Integer.compare(y, other.y);
if (x < other.x || (x == other.x && y < other.y)) {
return -1;
}
return x == other.x && y == other.y ? 0 : 1;
}
}
(Note that by convention the class name would be Node, not node.)
（请注意，按照惯例，类名应该是Node，而不是node。）
回答by Scorpion
Node needs to implement a Comparable or you need to pass a custom Comparator which can compare two Node objects. Also, any hash based collection relies on the object suitably overriding equals() and hashcode() method.
Node 需要实现一个 Comparable 或者你需要传递一个可以比较两个 Node 对象的自定义 Comparator。此外，任何基于散列的集合都依赖于适当覆盖 equals() 和 hashcode() 方法的对象。
回答by leifg
You have to specify equals, hashCode and implement the Comparable interface
您必须指定 equals、hashCode 并实现 Comparable 接口
回答by Santosh
There is nothing wrong with the code as for as acceptance is concerned. But for sorting Nodeclass MUST implement comparable interface.
就接受而言，代码没有任何问题。但是对于排序Node类必须实现可比较的接口。
