我正在研究一个霍夫曼编码程序，我差不多完成但是我陷入无限递归循环。有谁知道这出错了？
这是我得到的错误：
Exception in thread "main" java.lang.StackOverflowError
at sun.nio.cs.SingleByteEncoder.encodeLoop(SingleByteEncoder.java:130)
at java.nio.charset.CharsetEncoder.encode(CharsetEncoder.java:544)
at sun.nio.cs.StreamEncoder.implWrite(StreamEncoder.java:252)
at sun.nio.cs.StreamEncoder.write(StreamEncoder.java:106)
at java.io.OutputStreamWriter.write(OutputStreamWriter.java:190)
at java.io.BufferedWriter.flushBuffer(BufferedWriter.java:111)
at java.io.PrintStream.write(PrintStream.java:476)
at java.io.PrintStream.print(PrintStream.java:619)
at java.io.PrintStream.println(PrintStream.java:756)
at HuffmanNode.buildTree(hw4.java:63)
at HuffmanNode.buildTree(hw4.java:64)
at HuffmanNode.buildTree(hw4.java:64)
at HuffmanNode.buildTree(hw4.java:64)
at HuffmanNode.buildTree(hw4.java:64)
at HuffmanNode.buildTree(hw4.java:64)
at HuffmanNode.buildTree(hw4.java:64)
at HuffmanNode.buildTree(hw4.java:64)
并且输出连续5：1,5：4,5：2，重复
我的数据文件如下所示：
a
a
a
a
d
d
d
d
d
d
d
d
k
k
k
k
k
k
f
f
f
f
f
f
h
h
h
h
h
h
b
b
b
b
b
b
b
b
n
n
n
n
n
n
n
e
e
e
e
e
i
i
i
i
i
i
i
i
l
k
j
a
n
s
g
l
k
j
a
s
v
o
i
j
a
s
d
l
k
g
k
n
m
a
s
d
k
l
o
v
h
a
s
d
g
z
我的代码是
import java.util.*;
import java.io.*;
class HuffmanNode implements Comparable<HuffmanNode>{
HuffmanNode right;
HuffmanNode left;
HuffmanNode parent;
int count;
String letter;
public HuffmanNode(){}
public HuffmanNode (String letter, int count){
this.letter = letter;
this.count = count;
}
public HuffmanNode (String letter, int count, HuffmanNode parent, HuffmanNode left, HuffmanNode right){
this.letter = letter;
this.count = count;
this.left = left;
this.right = right;
this.parent = parent;
}
public void setCount(int count){
this.count = count;
}
public int getCount(){
return count;
}
public void setRight(HuffmanNode right){
this.right = right;
}
public HuffmanNode getRight(HuffmanNode right){
return right;
}
public void setLeft(HuffmanNode left){
this.left = left;
}
public HuffmanNode getLeft(HuffmanNode left){
return left;
}
public void setParent(HuffmanNode right){
this.left = left;
}
public HuffmanNode getParent(HuffmanNode parent){
return parent;
}
public void buildTree(HuffmanNode node){
if (node.compareTo(this) <= 0 && left != null){
System.out.println(node.getCount() + ":" + this.count);
left.buildTree(node);
}
else if (node.compareTo(this) <= 0 && left == null){
this.left = node;
node.parent = this;
}
else if (node.compareTo(this) > 0 && right != null){
System.out.println(node.getCount() + ":" +this.count);
right.buildTree(node);
}
else if (node.compareTo(this) > 0 && right == null){
this.right = node;
node.parent = this;
}
}
public int compareTo(HuffmanNode x){
return this.count - x.count;
}
public void genCode(String s){
if(left != null){
left.genCode(s + "0");
}
if(right != null){
right.genCode(s + "1");
}
if (left == null && right == null){
System.out.println(s);
}
}
}
public class hw4{
public static void main (String []args)throws IOException{
//ask user to enter file name
System.out.printf("Enter a file location and name to encode [press Enter]: ");
Scanner input = new Scanner(System.in);
String filename = input.next();
//Gets file name from Scanner and checks to see if valid
File file = new File(filename);
//if (!file.isFile()){
//System.out.printf("Enter a file location and name to encode [press Enter]: ");
//}
Scanner text = new Scanner(file);
String[] letters = {"a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"};
int[] freq = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
String letter;
String tempStr;
int tempInt;
while(text.hasNext()){
letter = text.next();
//System.out.printf("%s\n", letter);
char c = letter.charAt(0);
int index = c - 97;
freq[index]++;
}
for(int i=0; i <25; i++){
System.out.printf("%s:%d\n", letters[i], freq[i]);
}
System.out.printf("\n");
for (int n=0; n <25; n++) {
for (int i=0; i <25; i++) {
if (freq[i] > freq[i+1]) {
// exchange elements
tempInt = freq[i];
tempStr = letters[i];
freq[i] = freq[i+1];
letters[i] = letters[i+1];
freq[i+1] = tempInt;
letters[i+1] = tempStr;
}
}
}
PriorityQueue<HuffmanNode> huffmanList = new PriorityQueue<HuffmanNode>();
for(int i=0; i <26; i++){
System.out.printf("%s:%d\n", letters[i], freq[i]);
if(freq[i] > 0){
huffmanList.add(new HuffmanNode(letters[i],freq[i]));
}
}
HuffmanNode root = new HuffmanNode();
while(huffmanList.size() > 1){
HuffmanNode x = huffmanList.poll();
HuffmanNode y = huffmanList.poll();
HuffmanNode result = new HuffmanNode("-", x.getCount() + y.getCount(), null, x, y);
if(root == null){
root = result;
}
else{
root.buildTree(result);
}
huffmanList.add(result);
}
root.genCode(" ");
}
}
答案 0 :(得分：3)
你的树木造成了错误。
while(huffmanList.size() > 1){
HuffmanNode x = huffmanList.poll();
HuffmanNode y = huffmanList.poll();
你从队列中取出两个最轻的树，
HuffmanNode result = new HuffmanNode("-", x.getCount() + y.getCount(), null, x, y);
并合并它们，形成一个权重之和为权重的树 - 到目前为止，非常好。
if(root == null){ // never happens, but doesn't matter
root = result;
}
else{
root.buildTree(result);
然后将新形成的树插入root，
}
huffmanList.add(result);
}
并将其添加回队列。
现在，让我们考虑一个以
开头的队列(a,1), (b,2), (c,3), (d,3), (e,3), ...
root = new HuffmanNode();将root设置为(null, 0)。
首先，合并a和b个节点，提供<(a,1) | (-,3) | (b,2)>。插入root会产生
(null,0)
/ \
null (-,3)
/ \
(a,1) (b,2)
自3 > 0以来。队列是
<(a,1) | (-,3) | (b,2)>, (c,3), (d,3), (e,3) ...
插入合并树后[合并后的树也可以在几个权重3节点之后插入，那么它会花费更长的时间]。
现在，两个最轻的树被弹出并合并，给出了
<AB | (-,6) | (c,3)>
（缩写为AB = <(a,1) | (-,3) | (b,2)>）。然后将该树插入root树中。 6 > 0，因此它被插入到root，6 > 3的右侧子项中，因此它被插入到(-,3)，6 > 2的右子项中，因此它变为(b,2)节点的右子节点。但是，新合并树的左子节点和root的右子节点引用相同的对象，因此在插入之后，您有
__________
| |
v |
(null,0) (-,6) |
/ \ / \ |
null (-,3) (c,3) |
/ \ |
(a,1) (b,2) |
\_________|
一个应该是树的循环。接下来，弹出并合并两个节点(d,3)和(e,3)，给出一个权重为6的树，当该树插入root图时，它将循环。
不同的插入行为和/或不同的字母权重会改变细节，但事后root.buildTree(result);和huffmanList.add(result);队列包含对root所覆盖的图表的引用只要您最初有足够的节点，就会导致循环。一旦你有足够的周期，buildTree()调用不会在无限循环中着陆的可能性很小。
您根本不应该致电root.buildTree(result)。通过简单地合并队列中最轻的两个并重新插入结果来构造树，直到队列只包含一个树。
while(huffmanList.size() > 1){
HuffmanNode x = huffmanList.poll();
HuffmanNode y = huffmanList.poll();
HuffmanNode result = new HuffmanNode("-", x.getCount() + y.getCount(), null, x, y);
huffmanList.add(result);
}
root = huffmanList.poll();
答案 1 :(得分：0)
尝试更改
if(root.equals("null")){
到
if(root == null){
另外
尝试缩短您的数字if代码
char c = letter.charAt(0);
int index = c - 97;
freq[index]++;