我有一个稍微理论化的问题，在我开始编程我的解决方案之前我想要清理......
背景。 我需要在2个（或可能更多）MS Access文件之间进行比较。
每个文件都应包含在其他文件中找到的数据。
由于我遇到JDBC的“限制”并连接到Access结果集（它们只能向前滚动！）我创建了“java对象”（类）来模拟结果集的结构。
实质上 我有一个对象模拟结果集中的单个记录行（让我们称之为rowSet） 然后resSet对象有一个rowSets的“数组”。
然而，要“加快速度”，我会捕获键和索引列中的值，并将“key_Index”的hashMap创建到相关的rowSet对象。
我比较然后执行以下操作。
取第一个resSet对象（用作master），从中收集个人Key_Index的hashmaps（让我们称之为'aKey'....
现在使用这个'aKey'对象搜索其他可用的resSet对象，看看是否有任何包含与'aKey'中的值匹配的key_Index的值。
然而，我有一个相当恼人的想法。
如果我使用代码 resSet.get（的aKey） 在我的其他一个resSet对象上我会遇到问题，因为'aKey'对象显然不是同一个对象 - 尽管它的内容应该是相同的（即可比较的）。
我不得不说，当我阅读我的问题时，我认为它的措辞不够......所以我想我会包括我创建的课程副本......
重要部分：
成员： challenge - “结果集”类型对象的arrayList。
方法： runChallenge（）
package KWhite;
/**
* the RScomparator is designed for the instance of comparing a double entry database system, as
* often occurs in localy run medical trials data.
*
* The double entry is to ensure that there are no errors made during input, the entry is performed
* in separate independant instances. The RScolmparator object is specifically able to take any
* number of result sets as its input (ie queries from multiple independantly created databases)
*
* It should be recognised that this object should probably be called as part of a DBcomparator
* object.
*
*/
//imports here
//import of logger class and required dependencies...
import java.util.ArrayList;
import java.util.HashMap;
import org.apache.log4j.PropertyConfigurator;
import MrBlue.DB_Table;
import TawuaiLogger.tawuaiLogger;
public class RScomparator {
//Static variables
//the logger instance
private static final TawuaiLogger.tawuaiLogger errLog = new tawuaiLogger("RScomparator");
//class member variables
/** this is a selection of ResSet objects that are going to have thier data challenged */
private ArrayList<ResSet_KW> challenge;
/**the name of the current table being challenged*/
private String tableName;
/**a 'table' object for meta data reference purposes, this can be used for getting column types etc */
private DB_Table table;
//These are our report objects
/**a report array for challenge failures */
private ArrayList<report_KW> fail;
/**a report array for errors, ie no challenger able to be made, no equivalent value found */
private ArrayList<report_KW> errors;
/**a report array for the good values */
private ArrayList<report_KW> success;
/** this is either the main class or the constructor
*
* If it is a constructor rename to reflect the name of the class
* @param args
*/
public RScomparator(DB_Table t) //TODO add arguments as required
{
PropertyConfigurator.configure("Log4j.properties");
// TODO Auto-generated method stub
challenge = new ArrayList<ResSet_KW>();
//initialise our report objects for this challenge scenario
fail = new ArrayList<report_KW>();
errors = new ArrayList<report_KW>();
success = new ArrayList<report_KW>();
table = t;
tableName = t.getTblName();
}
//class methods go here
/**
* add a result set object into this comparator
*
* @param r the result set object being inserted into this challenge.
*
*/
public void addChallenger(ResSet_KW r)
{
this.challenge.add(r);
}
/**
* this runs the comparison process...
* Although no details in of itself are returned it calls other methods that do return a value
*
*/
public void runChallenge()
{
//TODO finish this method, creating a report object on the way
//these are the 2 result set objects that will be compared
ResSet_KW gold = new ResSet_KW ();
ResSet_KW silver = new ResSet_KW ();
//ensure the challenger list has objects in it.
if(challenge.size() < 2)
{
//it must have 2 objects..
errLog.add(3, "there are no results available for comparison of table " + this.tableName);
//either way we should create report object.
this.errors.add( new report_KW(tableName));
//break out of the method.
return;
}
//get the first row of data
gold = challenge.get(0);//the first result set.
//for each column in the result set, perform a search for the same key in the others..
for(HashMap<String, String> c : gold.getRS().keySet())
{//c is the key value in the map
//cycle over the challenge object
for (int i=1; i<challenge.size(); i++)//we don't want to use the first element, so start from 1 not zero
{
silver = challenge.get(i);
if (silver.hasKey(c))
{
//a temp object for meta data referencing
//only get the actual result values if there is a match
Column_KW a = gold.getRS().get(c);
Column_KW b = silver.getRS().get(c);
//make the comparison
a.compareTo(b, this.table);
//get the reports from the comparison
for(report_KW k :a.getFailure())
{
this.fail.add(k);
}
for(report_KW k :a.getPassed())
{
this.success.add(k);
}
for(report_KW k :a.getPassed())
{
this.errors.add(k);
}
}
else
{
break;//return to the next item in the for loop
}
}
}
}
/**
*a helper method to create the error message creator
*@ param m the extra message if any,
*@return s the full message
*/
private String getErrMessage(String m) {
//the third element in the current stact trace should be the calling method
StackTraceElement caller = Thread.currentThread().getStackTrace()[3];
String s = m + "\ncalled from line " + caller.getLineNumber()
+ "\nmethod: " + this.getClass() + "." + caller.getMethodName();
return s;
}
}//end class
PS。我的代码或更多欢迎
的任何内容提前致谢
大卫
编辑： 我刚刚发现了这个问题，Nested Maps or combined keys in java这将是我的解决方案，创建一个'自定义'key_Index对象，然后为它定义一个hashcode（）和equals对象。但是我已经为我的key_index对象使用了'hashMap'，所以这是在我没有注意到的地方自动执行的吗？
答案 0 :(得分：2)
你说：
如果我在其他一个resSet对象上使用代码resSet.get（aKey） 我会遇到问题，因为'aKey'对象显然不一样 object - 虽然它的内容应该相同（即可比较）。
您必须分别实施equals()和hashcode()。仅实现equals()是不够的，如果对象相等，hashcode()必须相同。
示例：
import java.util.HashMap;
import java.util.Map;
class A {
String name;
Integer number;
public A(String name, Integer number) {
super();
this.name = name;
this.number = number;
}
}
class B {
String name;
Integer number;
public B(String name, Integer number) {
super();
this.name = name;
this.number = number;
}
@Override
public boolean equals(Object obj) {
if (obj instanceof B) {
return obj == this || (name.equals(((B) obj).name) && number.equals(((B) obj).number));
}
return false;
}
@Override
public int hashCode() {
return name.hashCode() + number.hashCode();
}
}
public class TestHashMap {
public static void main(String... args) {
A a1 = new A("a", 1);
A anotherA1 = new A("a", 1);
Map<A, String> as = new HashMap<A, String>();
as.put(a1, "a1");
System.out.println(as.get(anotherA1)); // prints null
B b1 = new B("b", 1);
B anotherB1 = new B("b", 1);
Map<B, String> bs = new HashMap<B, String>();
bs.put(b1, "b1");
System.out.println(bs.get(anotherB1)); // prints b1
}
}