java – 在HashMap中找不到复合对象的密钥
内容导读
互联网集市收集整理的这篇技术教程文章主要介绍了java – 在HashMap中找不到复合对象的密钥，小编现在分享给大家，供广大互联网技能从业者学习和参考。文章包含6613字，纯文字阅读大概需要10分钟。
内容图文
所以,我用Java创建了自己的复合键,有3个成员
public class MyOwnKey{
int location;
int length;
String [] tokens;
}
现在我使用构造函数创建两个对象
String [] tokens = "Stackoverflow is great".split("\\s+");
Object key1 = new MyOwnKey(0,0,tokens)
tokens = "Web is great".split("\\s+");
Object key2 = new MyOwnKey(0,0,tokens)
现在,我在HashMap中添加密钥
HashMap map = new HashMap();
map.put(key1,1);
现在,这就是问题所在
当我包含密钥时,它会给出错误;
**map.containsKey(key2) //returns false whereas it should return true.**
这样才有意义：
key1.equals(key2) returns true
并且哈希码代码也相等. key1.hashCode()== key2.hashCode().
我已经实现了我自己的hashCode版本,toEquals()和toCompare().
不确定是什么问题.
这是代码
import java.io.DataOutput;
import java.io.DataInput;
import java.io.IOException;
import org.apache.hadoop.io.WritableComparable;
public class PatternGeneratorKey implements WritableComparable<Object> {
private String [] tokens;
int location;
int length;
StringBuffer _toString = null;
public PatternGeneratorKey(){
tokens = new String[1];
location =0;
length=1;
}
public PatternGeneratorKey(int location, int length, String [] tokens){
this.location = location;
this.length = length;
this.tokens= new String[tokens.length];
for(int i = 0; i < tokens.length;i++){
this.tokens[i] = tokens[i];
}
}
public int compareTo(Object o) {
if (!(o instanceof PatternGeneratorKey))
return -1;
return this.compareTo((PatternGeneratorKey) o);
}
public void write(DataOutput out) throws IOException {
out.writeInt(tokens.length);
for(int i = 0; i<tokens.length;i++){
out.writeUTF(tokens[i]);
}
out.writeInt(location);
out.writeInt(length);
}
public void readFields(DataInput in) throws IOException {
int l = in.readInt();
tokens = new String[l];
for(int i = 0; i < l ; i++){
tokens[i] = in.readUTF();
}
location = in.readInt();
length = in.readInt();
}
public int compareTo(PatternGeneratorKey k) {
if(this.tokens.length - this.length != k.tokens.length - k.length){
return this.tokens.length - this.length -( k.tokens.length - k.length);
}
if(this.location != k.location){
return this.location - k.location;
}
int i = 0 , j= 0;
for(i = 0, j=0 ; i < this.tokens.length && j < k.tokens.length;){
if(i == this.location ){
i = i + length;
continue;
}
if( j == k.location){
j = j + k.length;
continue;
}
if(!this.tokens[i].equalsIgnoreCase(k.tokens[j])){
return this.tokens[i].compareTo(k.tokens[j]);
}else{
i++;
j++;
}
}
//TODO: add comparison on left out phrase
return 0;
}
public int hashCode() {
int hashCode=0;
for(int i = 0; i < tokens.length;){
if(i == location ){
i = i + length;
continue;
}
hashCode += tokens[i++].hashCode();
}
hashCode+= location + tokens.length;
return hashCode;
}
public String toString(){
if(_toString == null){
_toString = new StringBuffer();
for(int k = 0; k < tokens.length ;k++){
if(k==location){
_toString.append(":").append(" ");
k=k+length-1;
}else{
_toString.append(tokens[k]).append(" ");
}
}
}
return _toString.toString();
}
public boolean equals(PatternGeneratorKey k) {
if(this.tokens.length - this.length == k.tokens.length - k.length
&& this.location == k.location){
//assume second one is larger
String tokens[] = k.tokens;
int length = k.length;
int location = k.location;
String [] tokens1 = this.tokens;
int length1 = this.length;
int location1 = this.location;
//make the local variable point to the largest of the two
if( this.tokens.length > k.tokens.length){
tokens = this.tokens;
length = this.length;
location = this.location;
tokens1 = k.tokens;
length1 = k.length;
location1 = k.location;
}
int i = 0 , j= 0;
for(i = 0, j=0 ; i < tokens.length;){
if(i == location ){
i = i + length;
continue;
}
// if( j >= location1 && j<= location1 + length1 -1){
if( j == location1){
j = j + length1;
continue;
}
if(!tokens[i++].equalsIgnoreCase(tokens1[j++])){
return false;
}
}
return true;
}else{
return false;
}
}
}
而且,这是我正在测试的代码
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.apache.hadoop.io.Text;
public class Test {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
String value = "gm used cars";
// Compile all the words using regex
String[] tokens = value.toString().split("\\s+");
//to find pattern we need atleast two words in the query
if(tokens.length <=1){
return;
}
Map<PatternGeneratorKey,List> map = new HashMap<PatternGeneratorKey, List>();
for(int l = 1 ; l < tokens.length; l++){
for(int i = 0 ; i < tokens.length - (l-1); i++){
String hit = new String(getPhrase(l, i, tokens));
PatternGeneratorKey key1 = new PatternGeneratorKey(i, l, tokens);
List list = null;
for(int k = 0;k< tokens.length;k++){
System.out.println("i:" + i + ",l:" + l + ",tokens:" + tokens[k]);
}
System.out.println("hashcode:" + key1.hashCode());
if(!map.containsKey(key1)){
list = new ArrayList<String>();
map.put(key1, list);
}else{
list = (List) map.get(key1);
}
list.add(hit);
}
}
value = "ford used cars";
String[] tokens2= value.toString().split("\\s+");
PatternGeneratorKey key2 = new PatternGeneratorKey(0, 1, tokens);
//run a sliding window for length 1 to tokens length -1
for(int l = 1 ; l < tokens2.length; l++){
//genereate token pairs with sliding window.
for(int i = 0 ; i < tokens2.length - (l-1); i++){
//hit a single token or a + b if there are two.
String hit = new String(getPhrase(l, i, tokens2));
PatternGeneratorKey key1 = new PatternGeneratorKey(i, l, tokens2);
System.out.println();
System.out.println(key1.toString() + "|" + key2.toString() + "|"+ key1.equals(key2));
for(int k = 0;k< tokens2.length;k++){
System.out.println("i:" + i + ",l:" + l + ",tokens:" + tokens2[k]);
}
System.out.println("hashcode:" + key1.hashCode());
List list = null;
if(!map.containsKey(key1)){
list = new ArrayList<String>();
map.put(key1, list);
}else{
list = (List) map.get(key1);
}
list.add(hit);
}
}
value = "ford used cars";
tokens= value.toString().split("\\s+");
PatternGeneratorKey key1 = new PatternGeneratorKey(0,1,tokens);
tokens2 = "gm used cars".split("\\s+");
key2 = new PatternGeneratorKey(0,1,tokens2);
System.out.println(key1.equals(key2));
System.out.println(key2.equals(key1));
System.out.println(key1.hashCode() );
System.out.println(key2.hashCode() );
System.out.println(map);
}
private static String getPhrase(int l, int i, String[] tokens){
StringBuffer strin = new StringBuffer();
int index = 0;
for(index = i ; index < i+l;index++){
if(index < i+l-1){
strin.append(tokens[index]).append("+");
}
else
{
strin.append(tokens[index]);
}
}
return strin.toString();
}
}
解决方法:
你的问题是由equals(PatternGeneratorKey)不重写equals(Object)(但它重载equals(Object)这一事实引起的,所以当key1和key2是PatternGeneratorKey类型的变量时,key1.equals(key2)返回true！) .
由于HashMap调用equals(Object)来检查键是否相等,因此您的方法永远不会被调用,因此您需要实现equals(Object).
内容总结
以上是互联网集市为您收集整理的java – 在HashMap中找不到复合对象的密钥全部内容，希望文章能够帮你解决java – 在HashMap中找不到复合对象的密钥所遇到的程序开发问题。 如果觉得互联网集市技术教程内容还不错，欢迎将互联网集市网站推荐给程序员好友。
内容备注
版权声明：本文内容由互联网用户自发贡献，该文观点与技术仅代表作者本人。本站仅提供信息存储空间服务，不拥有所有权，不承担相关法律责任。如发现本站有涉嫌侵权/违法违规的内容， 请发送邮件至 gblab@vip.qq.com 举报，一经查实，本站将立刻删除。
内容手机端
扫描二维码推送至手机访问。
来源：【匿名】