[英]adding a specified comparator to java priorityqueue
Im having a hard time understanding how to priorityqueue uses the compareTo method to sort its content.我很难理解如何优先排队使用 compareTo 方法对其内容进行排序。
I have on class called Node.我有一个名为 Node.js 的课程。 and its has 4 fields.它有4个字段。
private char character;
private int frequency;
private Node left_child;
private Node right_child;
Then in my other class called Huffmantree I have a priorityqueue.然后在我的另一个名为 Huffmantree 的班级中,我有一个优先队列。
My problem:我的问题:
I want to put object nodes in the queue so that when dequeueing it depends on the (int)frequency of the node.我想将对象节点放入队列中,以便在出队时它取决于节点的(int)频率。
Now my Node class look like this:现在我的 Node 类看起来像这样:
/**
* Class for creating nodes with a specified character, frequency,
* left- and right child.
* implements comparable to be able to compare 2 nodes based on their
* frequency.
*/
public class Node implements Comparable<Node>{
private char character;
private int frequency;
private Node left_child;
private Node right_child;
public Node(char character, int frequency, Node left_child, Node
right_child){
this.character = character;
this.frequency = frequency;
this.left_child = left_child;
this.right_child = right_child;
}
//Checks if two nodes have equal frequency.
private boolean equals(Node n){
return this.frequency == n.frequency;
}
@Override
public int compareTo(Node other) {
if(this.equals(other)){
return 0;
}else if(this.frequency > other.frequency){
return 1;
}else return -1;
}
//Print out current node
@Override
public String toString(){
return "[" +this.character+"," + this.frequency +"]";
}
Here I have tried to implement the Comparable interface and I have defined a CompareTo method, comparing Nodes to their frequency value.在这里,我尝试实现 Comparable 接口,并定义了一个 CompareTo 方法,将节点与其频率值进行比较。
In my HuffmanTree class I have tried to make a priorityqueue like this:在我的 HuffmanTree 类中,我尝试创建一个像这样的优先队列:
PriorityQueue<Node> pq = new PriorityQueue<>(new Comparator<Node>()
but i dont know if this is how u would do it.但我不知道这是否是你的方式。 I´m stuck and I haven't found a good example of this.我被卡住了,我还没有找到一个很好的例子。
Since your Node
class already implements the Comparable
interface, there is no need to define a Comparator<Node>
and pass it to your queue object, just use the no-argument constructor :由于您的Node
类已经实现了Comparable
接口,因此无需定义Comparator<Node>
并将其传递给您的队列对象,只需使用无参数构造函数:
PriorityQueue<Node> pq = new PriorityQueue<>();
According to the official documentation :根据官方文档:
public PriorityQueue()
Creates a PriorityQueue with the default initial capacity (11) that orders its elements according to their natural ordering.创建一个具有默认初始容量 (11) 的 PriorityQueue,根据元素的自然顺序对其进行排序。
In this case, you have defined a natural ordering by implementing the compareTo
method for your Node
objects, so you're pretty much done.在本例中,您已经通过为Node
对象实现compareTo
方法来定义自然排序,因此您已经大功告成了。 The other constructor which takes a comparator must only be used if the elements in your queue are not Comparable
s, or you wish to use a different ordering :只有当队列中的元素不是Comparable
s,或者您希望使用不同的 ordering 时,才必须使用采用比较器的另一个构造函数:
// This queue will hand out nodes in the inverse order of their frequency
PriorityQueue<Node> queue = new PriorityQueue<>(new Comparator<Node>() {
@Override
public int compare(Node a, Node b) {
return -a.compareTo(b);
}
});
The compareTo() is used to compare two objects. compareTo() 用于比较两个对象。
So if you want to compare based on the frequency then you should write:所以如果你想根据频率进行比较,那么你应该写:
public int compareTo(Node other) {
if(frequency>other.frequency)
return 1;
else if(frequency==other.frequency)
return 0;
return -1;
}
Here we are comparing the current frequency with the parametrized object.在这里,我们将当前频率与参数化对象进行比较。
You can get a detail description from here您可以从这里获得详细说明
And you dont need this:你不需要这个:
PriorityQueue pq = new PriorityQueue<>(new Comparator()) PriorityQueue pq = new PriorityQueue<>(new Comparator())
You can just write this:你可以这样写:
PriorityQueue pq = new PriorityQueue<>(); PriorityQueue pq = new PriorityQueue<>();
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